Merge pull request #1010 from Zokrates/ternary

Ternary operator

changelogs/unreleased/1010-dark64

@@ -0,0 +1 @@
+Introduce ternary operator

zokrates_book/src/language/control_flow.md

@@ -26,6 +26,12 @@ An if-expression allows you to branch your code depending on a boolean condition
 {{#include ../../../zokrates_cli/examples/book/if_else.zok}}
 ```
 
+The conditional expression can also be written using a ternary operator:
+
+```zokrates
+{{#include ../../../zokrates_cli/examples/book/ternary.zok}}
+```
+
 There are two important caveats when it comes to conditional expressions. Before we go into them, let's define two concepts:
 - for an execution of the program, *an executed branch* is a branch which has to be paid for when executing the program, generating proofs, etc.
 - for an execution of the program, *a logically executed branch* is a branch which is "chosen" by the condition of an if-expression. This is the more intuitive notion of execution, and there is only one for each if-expression.

zokrates_book/src/language/operators.md

@@ -16,10 +16,12 @@ The following table lists the precedence and associativity of all operators. Ope
 | `!=`<br>`==`<br>           | Not Equal<br>Equal<br>                                     | &check;                      | &check;                       | &check;                     | Left          |         |
 | `&&`                       | Boolean AND                                                | &nbsp;                       | &nbsp;                        | &check;                     | Left          |         |
 | <code>&#124;&#124;</code>  | Boolean OR                                                 | &nbsp;                       | &nbsp;                        | &check;                     | Left          |         |
-| `if c then x else y fi`    | Conditional expression                                     | &check;                      | &check;                       | &check;                     | Right         |         |
+| `if c then x else y fi`    | Conditional expression                                     | &check;                      | &check;                       | &check;                     | Right         | [^4]    |
 
 [^1]: The exponent must be a compile-time constant of type `u32`
 
 [^2]: The right operand must be a compile time constant of type `u32`
 
 [^3]: Both operands are asserted to be strictly lower than the biggest power of 2 lower than `p/2`, unless one of them can be determined to be a compile-time constant
+
+[^4]: Conditional expression can also be written using a ternary operator: `c ? x : y`

zokrates_cli/examples/book/ternary.zok

@@ -0,0 +1,3 @@
+def main(field x) -> field:
+  field y = x + 2 == 3 ? 1 : 5
+  return y

zokrates_cli/examples/compile_errors/ternary_precedence.zok

@@ -0,0 +1,5 @@
+def main(bool a) -> field:
+    // ternary expression should be wrapped in parentheses 1 + (a ? 2 : 3)
+    // otherwise the whole expression is parsed as (1 + a) ? 2 : 3
+    field x = 1 + a ? 2 : 3
+    return x

zokrates_core/src/absy/from_ast.rs

@@ -378,6 +378,7 @@ impl<'ast> From<pest::Expression<'ast>> for absy::ExpressionNode<'ast> {
         match expression {
             pest::Expression::Binary(e) => absy::ExpressionNode::from(e),
             pest::Expression::Ternary(e) => absy::ExpressionNode::from(e),
+            pest::Expression::IfElse(e) => absy::ExpressionNode::from(e),
             pest::Expression::Literal(e) => absy::ExpressionNode::from(e),
             pest::Expression::Identifier(e) => absy::ExpressionNode::from(e),
             pest::Expression::Postfix(e) => absy::ExpressionNode::from(e),
@@ -478,13 +479,27 @@ impl<'ast> From<pest::BinaryExpression<'ast>> for absy::ExpressionNode<'ast> {
     }
 }
 
+impl<'ast> From<pest::IfElseExpression<'ast>> for absy::ExpressionNode<'ast> {
+    fn from(expression: pest::IfElseExpression<'ast>) -> absy::ExpressionNode<'ast> {
+        use crate::absy::NodeValue;
+        absy::Expression::Conditional(
+            box absy::ExpressionNode::from(*expression.condition),
+            box absy::ExpressionNode::from(*expression.consequence),
+            box absy::ExpressionNode::from(*expression.alternative),
+            absy::ConditionalKind::IfElse,
+        )
+        .span(expression.span)
+    }
+}
+
 impl<'ast> From<pest::TernaryExpression<'ast>> for absy::ExpressionNode<'ast> {
     fn from(expression: pest::TernaryExpression<'ast>) -> absy::ExpressionNode<'ast> {
         use crate::absy::NodeValue;
-        absy::Expression::IfElse(
-            box absy::ExpressionNode::from(*expression.first),
-            box absy::ExpressionNode::from(*expression.second),
-            box absy::ExpressionNode::from(*expression.third),
+        absy::Expression::Conditional(
+            box absy::ExpressionNode::from(*expression.condition),
+            box absy::ExpressionNode::from(*expression.consequence),
+            box absy::ExpressionNode::from(*expression.alternative),
+            absy::ConditionalKind::Ternary,
         )
         .span(expression.span)
     }

zokrates_core/src/absy/mod.rs

@@ -460,6 +460,12 @@ impl<'ast> fmt::Display for Range<'ast> {
     }
 }
 
+#[derive(Debug, Clone, PartialEq)]
+pub enum ConditionalKind {
+    IfElse,
+    Ternary,
+}
+
 /// An expression
 #[derive(Debug, Clone, PartialEq)]
 pub enum Expression<'ast> {
@@ -479,10 +485,11 @@ pub enum Expression<'ast> {
     Pow(Box<ExpressionNode<'ast>>, Box<ExpressionNode<'ast>>),
     Neg(Box<ExpressionNode<'ast>>),
     Pos(Box<ExpressionNode<'ast>>),
-    IfElse(
+    Conditional(
         Box<ExpressionNode<'ast>>,
         Box<ExpressionNode<'ast>>,
         Box<ExpressionNode<'ast>>,
+        ConditionalKind,
     ),
     FunctionCall(
         Box<ExpressionNode<'ast>>,
@@ -530,11 +537,18 @@ impl<'ast> fmt::Display for Expression<'ast> {
             Expression::Neg(ref e) => write!(f, "(-{})", e),
             Expression::Pos(ref e) => write!(f, "(+{})", e),
             Expression::BooleanConstant(b) => write!(f, "{}", b),
-            Expression::IfElse(ref condition, ref consequent, ref alternative) => write!(
-                f,
-                "if {} then {} else {} fi",
-                condition, consequent, alternative
-            ),
+            Expression::Conditional(ref condition, ref consequent, ref alternative, ref kind) => {
+                match kind {
+                    ConditionalKind::IfElse => write!(
+                        f,
+                        "if {} then {} else {} fi",
+                        condition, consequent, alternative
+                    ),
+                    ConditionalKind::Ternary => {
+                        write!(f, "{} ? {} : {}", condition, consequent, alternative)
+                    }
+                }
+            }
             Expression::FunctionCall(ref i, ref g, ref p) => {
                 if let Some(g) = g {
                     write!(

zokrates_core/src/semantics.rs

@@ -2270,7 +2270,7 @@ impl<'ast, T: Field> Checker<'ast, T> {
                     }),
                 }
             }
-            Expression::IfElse(box condition, box consequence, box alternative) => {
+            Expression::Conditional(box condition, box consequence, box alternative, kind) => {
                 let condition_checked = self.check_expression(condition, module_id, types)?;
                 let consequence_checked = self.check_expression(consequence, module_id, types)?;
                 let alternative_checked = self.check_expression(alternative, module_id, types)?;
@@ -2282,40 +2282,49 @@ impl<'ast, T: Field> Checker<'ast, T> {
                     )
                     .map_err(|(e1, e2)| ErrorInner {
                         pos: Some(pos),
-                        message: format!("{{consequence}} and {{alternative}} in `if/else` expression should have the same type, found {}, {}", e1.get_type(), e2.get_type()),
+                        message: format!("{{consequence}} and {{alternative}} in conditional expression should have the same type, found {}, {}", e1.get_type(), e2.get_type()),
                     })?;
 
+                let kind = match kind {
+                    crate::absy::ConditionalKind::IfElse => {
+                        crate::typed_absy::ConditionalKind::IfElse
+                    }
+                    crate::absy::ConditionalKind::Ternary => {
+                        crate::typed_absy::ConditionalKind::Ternary
+                    }
+                };
+
                 match condition_checked {
                     TypedExpression::Boolean(condition) => {
                         match (consequence_checked, alternative_checked) {
                             (TypedExpression::FieldElement(consequence), TypedExpression::FieldElement(alternative)) => {
-                                Ok(FieldElementExpression::if_else(condition, consequence, alternative).into())
+                                Ok(FieldElementExpression::conditional(condition, consequence, alternative, kind).into())
                             },
                             (TypedExpression::Boolean(consequence), TypedExpression::Boolean(alternative)) => {
-                                Ok(BooleanExpression::if_else(condition, consequence, alternative).into())
+                                Ok(BooleanExpression::conditional(condition, consequence, alternative, kind).into())
                             },
                             (TypedExpression::Array(consequence), TypedExpression::Array(alternative)) => {
-                                Ok(ArrayExpression::if_else(condition, consequence, alternative).into())
+                                Ok(ArrayExpression::conditional(condition, consequence, alternative, kind).into())
                             },
                             (TypedExpression::Struct(consequence), TypedExpression::Struct(alternative)) => {
-                                Ok(StructExpression::if_else(condition, consequence, alternative).into())
+                                Ok(StructExpression::conditional(condition, consequence, alternative, kind).into())
                             },
                             (TypedExpression::Uint(consequence), TypedExpression::Uint(alternative)) => {
-                                Ok(UExpression::if_else(condition, consequence, alternative).into())
+                                Ok(UExpression::conditional(condition, consequence, alternative, kind).into())
                             },
                             (TypedExpression::Int(consequence), TypedExpression::Int(alternative)) => {
-                                Ok(IntExpression::if_else(condition, consequence, alternative).into())
+                                Ok(IntExpression::conditional(condition, consequence, alternative, kind).into())
                             },
                             (c, a) => Err(ErrorInner {
                                 pos: Some(pos),
-                                message: format!("{{consequence}} and {{alternative}} in `if/else` expression should have the same type, found {}, {}", c.get_type(), a.get_type())
+                                message: format!("{{consequence}} and {{alternative}} in conditional expression should have the same type, found {}, {}", c.get_type(), a.get_type())
                             })
                         }
                     }
                     c => Err(ErrorInner {
                         pos: Some(pos),
                         message: format!(
-                            "{{condition}} after `if` should be a boolean, found {}",
+                            "{{condition}} should be a boolean, found {}",
                             c.get_type()
                         ),
                     }),

zokrates_core/src/static_analysis/branch_isolator.rs

@@ -17,17 +17,18 @@ impl Isolator {
 }
 
 impl<'ast, T: Field> Folder<'ast, T> for Isolator {
-    fn fold_if_else_expression<
-        E: Expr<'ast, T> + Block<'ast, T> + Fold<'ast, T> + IfElse<'ast, T>,
+    fn fold_conditional_expression<
+        E: Expr<'ast, T> + Block<'ast, T> + Fold<'ast, T> + Conditional<'ast, T>,
     >(
         &mut self,
         _: &E::Ty,
-        e: IfElseExpression<'ast, T, E>,
-    ) -> IfElseOrExpression<'ast, T, E> {
-        IfElseOrExpression::IfElse(IfElseExpression::new(
+        e: ConditionalExpression<'ast, T, E>,
+    ) -> ConditionalOrExpression<'ast, T, E> {
+        ConditionalOrExpression::Conditional(ConditionalExpression::new(
             self.fold_boolean_expression(*e.condition),
             E::block(vec![], e.consequence.fold(self)),
             E::block(vec![], e.alternative.fold(self)),
+            e.kind,
         ))
     }
 }

zokrates_core/src/static_analysis/flatten_complex_types.rs

@@ -281,12 +281,12 @@ impl<'ast, T: Field> Flattener<T> {
         }
     }
 
-    fn fold_if_else_expression<E: Flatten<'ast, T>>(
+    fn fold_conditional_expression<E: Flatten<'ast, T>>(
         &mut self,
         statements_buffer: &mut Vec<zir::ZirStatement<'ast, T>>,
-        c: typed_absy::IfElseExpression<'ast, T, E>,
+        c: typed_absy::ConditionalExpression<'ast, T, E>,
     ) -> Vec<zir::ZirExpression<'ast, T>> {
-        fold_if_else_expression(self, statements_buffer, c)
+        fold_conditional_expression(self, statements_buffer, c)
     }
 
     fn fold_member_expression<E>(
@@ -448,8 +448,8 @@ fn fold_array_expression_inner<'ast, T: Field>(
             exprs
         }
         typed_absy::ArrayExpressionInner::FunctionCall(..) => unreachable!(),
-        typed_absy::ArrayExpressionInner::IfElse(c) => {
-            f.fold_if_else_expression(statements_buffer, c)
+        typed_absy::ArrayExpressionInner::Conditional(c) => {
+            f.fold_conditional_expression(statements_buffer, c)
         }
         typed_absy::ArrayExpressionInner::Member(m) => {
             f.fold_member_expression(statements_buffer, m)
@@ -523,8 +523,8 @@ fn fold_struct_expression_inner<'ast, T: Field>(
             .flat_map(|e| f.fold_expression(statements_buffer, e))
             .collect(),
         typed_absy::StructExpressionInner::FunctionCall(..) => unreachable!(),
-        typed_absy::StructExpressionInner::IfElse(c) => {
-            f.fold_if_else_expression(statements_buffer, c)
+        typed_absy::StructExpressionInner::Conditional(c) => {
+            f.fold_conditional_expression(statements_buffer, c)
         }
         typed_absy::StructExpressionInner::Member(m) => {
             f.fold_member_expression(statements_buffer, m)
@@ -646,10 +646,10 @@ fn fold_select_expression<'ast, T: Field, E>(
     }
 }
 
-fn fold_if_else_expression<'ast, T: Field, E: Flatten<'ast, T>>(
+fn fold_conditional_expression<'ast, T: Field, E: Flatten<'ast, T>>(
     f: &mut Flattener<T>,
     statements_buffer: &mut Vec<zir::ZirStatement<'ast, T>>,
-    c: typed_absy::IfElseExpression<'ast, T, E>,
+    c: typed_absy::ConditionalExpression<'ast, T, E>,
 ) -> Vec<zir::ZirExpression<'ast, T>> {
     let mut consequence_statements = vec![];
     let mut alternative_statements = vec![];
@@ -742,8 +742,8 @@ fn fold_field_expression<'ast, T: Field>(
         typed_absy::FieldElementExpression::Pos(box e) => {
             f.fold_field_expression(statements_buffer, e)
         }
-        typed_absy::FieldElementExpression::IfElse(c) => f
-            .fold_if_else_expression(statements_buffer, c)
+        typed_absy::FieldElementExpression::Conditional(c) => f
+            .fold_conditional_expression(statements_buffer, c)
             .pop()
             .unwrap()
             .try_into()
@@ -908,8 +908,8 @@ fn fold_boolean_expression<'ast, T: Field>(
             let e = f.fold_boolean_expression(statements_buffer, e);
             zir::BooleanExpression::Not(box e)
         }
-        typed_absy::BooleanExpression::IfElse(c) => f
-            .fold_if_else_expression(statements_buffer, c)
+        typed_absy::BooleanExpression::Conditional(c) => f
+            .fold_conditional_expression(statements_buffer, c)
             .pop()
             .unwrap()
             .try_into()
@@ -1070,8 +1070,8 @@ fn fold_uint_expression_inner<'ast, T: Field>(
         )
         .unwrap()
         .into_inner(),
-        typed_absy::UExpressionInner::IfElse(c) => zir::UExpression::try_from(
-            f.fold_if_else_expression(statements_buffer, c)
+        typed_absy::UExpressionInner::Conditional(c) => zir::UExpression::try_from(
+            f.fold_conditional_expression(statements_buffer, c)
                 .pop()
                 .unwrap(),
         )

zokrates_core/src/static_analysis/propagation.rs

@@ -172,13 +172,13 @@ impl<'ast, 'a, T: Field> ResultFolder<'ast, T> for Propagator<'ast, 'a, T> {
         fold_function(self, f)
     }
 
-    fn fold_if_else_expression<
-        E: Expr<'ast, T> + IfElse<'ast, T> + PartialEq + ResultFold<'ast, T>,
+    fn fold_conditional_expression<
+        E: Expr<'ast, T> + Conditional<'ast, T> + PartialEq + ResultFold<'ast, T>,
     >(
         &mut self,
         _: &E::Ty,
-        e: IfElseExpression<'ast, T, E>,
-    ) -> Result<IfElseOrExpression<'ast, T, E>, Self::Error> {
+        e: ConditionalExpression<'ast, T, E>,
+    ) -> Result<ConditionalOrExpression<'ast, T, E>, Self::Error> {
         Ok(
             match (
                 self.fold_boolean_expression(*e.condition)?,
@@ -186,16 +186,16 @@ impl<'ast, 'a, T: Field> ResultFolder<'ast, T> for Propagator<'ast, 'a, T> {
                 e.alternative.fold(self)?,
             ) {
                 (BooleanExpression::Value(true), consequence, _) => {
-                    IfElseOrExpression::Expression(consequence.into_inner())
+                    ConditionalOrExpression::Expression(consequence.into_inner())
                 }
                 (BooleanExpression::Value(false), _, alternative) => {
-                    IfElseOrExpression::Expression(alternative.into_inner())
+                    ConditionalOrExpression::Expression(alternative.into_inner())
                 }
                 (_, consequence, alternative) if consequence == alternative => {
-                    IfElseOrExpression::Expression(consequence.into_inner())
+                    ConditionalOrExpression::Expression(consequence.into_inner())
                 }
-                (condition, consequence, alternative) => IfElseOrExpression::IfElse(
-                    IfElseExpression::new(condition, consequence, alternative),
+                (condition, consequence, alternative) => ConditionalOrExpression::Conditional(
+                    ConditionalExpression::new(condition, consequence, alternative, e.kind),
                 ),
             },
         )
@@ -1431,10 +1431,11 @@ mod tests {
 
             #[test]
             fn if_else_true() {
-                let e = FieldElementExpression::if_else(
+                let e = FieldElementExpression::conditional(
                     BooleanExpression::Value(true),
                     FieldElementExpression::Number(Bn128Field::from(2)),
                     FieldElementExpression::Number(Bn128Field::from(3)),
+                    ConditionalKind::IfElse,
                 );
 
                 assert_eq!(
@@ -1445,10 +1446,11 @@ mod tests {
 
             #[test]
             fn if_else_false() {
-                let e = FieldElementExpression::if_else(
+                let e = FieldElementExpression::conditional(
                     BooleanExpression::Value(false),
                     FieldElementExpression::Number(Bn128Field::from(2)),
                     FieldElementExpression::Number(Bn128Field::from(3)),
+                    ConditionalKind::IfElse,
                 );
 
                 assert_eq!(

zokrates_core/src/static_analysis/variable_write_remover.rs

@@ -56,7 +56,7 @@ impl<'ast> VariableWriteRemover {
                                 (0..size)
                                     .map(|i| match inner_ty {
                                         Type::Int => unreachable!(),
-                                        Type::Array(..) => ArrayExpression::if_else(
+                                        Type::Array(..) => ArrayExpression::conditional(
                                             BooleanExpression::UintEq(
                                                 box i.into(),
                                                 box head.clone(),
@@ -74,9 +74,10 @@ impl<'ast> VariableWriteRemover {
                                         ),
                                             },
                                             ArrayExpression::select(base.clone(), i),
+                                            ConditionalKind::IfElse,
                                         )
                                         .into(),
-                                        Type::Struct(..) => StructExpression::if_else(
+                                        Type::Struct(..) => StructExpression::conditional(
                                             BooleanExpression::UintEq(
                                                 box i.into(),
                                                 box head.clone(),
@@ -94,9 +95,10 @@ impl<'ast> VariableWriteRemover {
                                         ),
                                             },
                                             StructExpression::select(base.clone(), i),
+                                            ConditionalKind::IfElse,
                                         )
                                         .into(),
-                                        Type::FieldElement => FieldElementExpression::if_else(
+                                        Type::FieldElement => FieldElementExpression::conditional(
                                             BooleanExpression::UintEq(
                                                 box i.into(),
                                                 box head.clone(),
@@ -115,9 +117,10 @@ impl<'ast> VariableWriteRemover {
                                         ),
                                             },
                                             FieldElementExpression::select(base.clone(), i),
+                                            ConditionalKind::IfElse,
                                         )
                                         .into(),
-                                        Type::Boolean => BooleanExpression::if_else(
+                                        Type::Boolean => BooleanExpression::conditional(
                                             BooleanExpression::UintEq(
                                                 box i.into(),
                                                 box head.clone(),
@@ -135,9 +138,10 @@ impl<'ast> VariableWriteRemover {
                                         ),
                                             },
                                             BooleanExpression::select(base.clone(), i),
+                                            ConditionalKind::IfElse,
                                         )
                                         .into(),
-                                        Type::Uint(..) => UExpression::if_else(
+                                        Type::Uint(..) => UExpression::conditional(
                                             BooleanExpression::UintEq(
                                                 box i.into(),
                                                 box head.clone(),
@@ -155,6 +159,7 @@ impl<'ast> VariableWriteRemover {
                                         ),
                                             },
                                             UExpression::select(base.clone(), i),
+                                            ConditionalKind::IfElse,
                                         )
                                         .into(),
                                     })

zokrates_core/src/typed_absy/folder.rs

@@ -284,18 +284,18 @@ pub trait Folder<'ast, T: Field>: Sized {
         fold_block_expression(self, block)
     }
 
-    fn fold_if_else_expression<
+    fn fold_conditional_expression<
         E: Expr<'ast, T>
             + Fold<'ast, T>
             + Block<'ast, T>
-            + IfElse<'ast, T>
+            + Conditional<'ast, T>
             + From<TypedExpression<'ast, T>>,
     >(
         &mut self,
         ty: &E::Ty,
-        e: IfElseExpression<'ast, T, E>,
-    ) -> IfElseOrExpression<'ast, T, E> {
-        fold_if_else_expression(self, ty, e)
+        e: ConditionalExpression<'ast, T, E>,
+    ) -> ConditionalOrExpression<'ast, T, E> {
+        fold_conditional_expression(self, ty, e)
     }
 
     fn fold_member_expression<
@@ -319,7 +319,7 @@ pub trait Folder<'ast, T: Field>: Sized {
     }
 
     fn fold_select_expression<
-        E: Expr<'ast, T> + Select<'ast, T> + IfElse<'ast, T> + From<TypedExpression<'ast, T>>,
+        E: Expr<'ast, T> + Select<'ast, T> + Conditional<'ast, T> + From<TypedExpression<'ast, T>>,
     >(
         &mut self,
         ty: &E::Ty,
@@ -506,9 +506,9 @@ pub fn fold_array_expression_inner<'ast, T: Field, F: Folder<'ast, T>>(
                 FunctionCallOrExpression::Expression(u) => u,
             }
         }
-        ArrayExpressionInner::IfElse(c) => match f.fold_if_else_expression(ty, c) {
-            IfElseOrExpression::IfElse(s) => ArrayExpressionInner::IfElse(s),
-            IfElseOrExpression::Expression(u) => u,
+        ArrayExpressionInner::Conditional(c) => match f.fold_conditional_expression(ty, c) {
+            ConditionalOrExpression::Conditional(s) => ArrayExpressionInner::Conditional(s),
+            ConditionalOrExpression::Expression(u) => u,
         },
         ArrayExpressionInner::Select(select) => match f.fold_select_expression(ty, select) {
             SelectOrExpression::Select(s) => ArrayExpressionInner::Select(s),
@@ -553,9 +553,9 @@ pub fn fold_struct_expression_inner<'ast, T: Field, F: Folder<'ast, T>>(
                 FunctionCallOrExpression::Expression(u) => u,
             }
         }
-        StructExpressionInner::IfElse(c) => match f.fold_if_else_expression(ty, c) {
-            IfElseOrExpression::IfElse(s) => StructExpressionInner::IfElse(s),
-            IfElseOrExpression::Expression(u) => u,
+        StructExpressionInner::Conditional(c) => match f.fold_conditional_expression(ty, c) {
+            ConditionalOrExpression::Conditional(s) => StructExpressionInner::Conditional(s),
+            ConditionalOrExpression::Expression(u) => u,
         },
         StructExpressionInner::Select(select) => match f.fold_select_expression(ty, select) {
             SelectOrExpression::Select(s) => StructExpressionInner::Select(s),
@@ -615,10 +615,10 @@ pub fn fold_field_expression<'ast, T: Field, F: Folder<'ast, T>>(
 
             FieldElementExpression::Pos(box e)
         }
-        FieldElementExpression::IfElse(c) => {
-            match f.fold_if_else_expression(&Type::FieldElement, c) {
-                IfElseOrExpression::IfElse(s) => FieldElementExpression::IfElse(s),
-                IfElseOrExpression::Expression(u) => u,
+        FieldElementExpression::Conditional(c) => {
+            match f.fold_conditional_expression(&Type::FieldElement, c) {
+                ConditionalOrExpression::Conditional(s) => FieldElementExpression::Conditional(s),
+                ConditionalOrExpression::Expression(u) => u,
             }
         }
         FieldElementExpression::FunctionCall(function_call) => {
@@ -643,20 +643,21 @@ pub fn fold_field_expression<'ast, T: Field, F: Folder<'ast, T>>(
     }
 }
 
-pub fn fold_if_else_expression<
+pub fn fold_conditional_expression<
     'ast,
     T: Field,
-    E: Expr<'ast, T> + Fold<'ast, T> + IfElse<'ast, T> + From<TypedExpression<'ast, T>>,
+    E: Expr<'ast, T> + Fold<'ast, T> + Conditional<'ast, T> + From<TypedExpression<'ast, T>>,
     F: Folder<'ast, T>,
 >(
     f: &mut F,
     _: &E::Ty,
-    e: IfElseExpression<'ast, T, E>,
-) -> IfElseOrExpression<'ast, T, E> {
-    IfElseOrExpression::IfElse(IfElseExpression::new(
+    e: ConditionalExpression<'ast, T, E>,
+) -> ConditionalOrExpression<'ast, T, E> {
+    ConditionalOrExpression::Conditional(ConditionalExpression::new(
         f.fold_boolean_expression(*e.condition),
         e.consequence.fold(f),
         e.alternative.fold(f),
+        e.kind,
     ))
 }
 
@@ -679,7 +680,7 @@ pub fn fold_member_expression<
 pub fn fold_select_expression<
     'ast,
     T: Field,
-    E: Expr<'ast, T> + Select<'ast, T> + IfElse<'ast, T> + From<TypedExpression<'ast, T>>,
+    E: Expr<'ast, T> + Select<'ast, T> + Conditional<'ast, T> + From<TypedExpression<'ast, T>>,
     F: Folder<'ast, T>,
 >(
     f: &mut F,
@@ -794,9 +795,10 @@ pub fn fold_boolean_expression<'ast, T: Field, F: Folder<'ast, T>>(
                 FunctionCallOrExpression::Expression(u) => u,
             }
         }
-        BooleanExpression::IfElse(c) => match f.fold_if_else_expression(&Type::Boolean, c) {
-            IfElseOrExpression::IfElse(s) => BooleanExpression::IfElse(s),
-            IfElseOrExpression::Expression(u) => u,
+        BooleanExpression::Conditional(c) => match f.fold_conditional_expression(&Type::Boolean, c)
+        {
+            ConditionalOrExpression::Conditional(s) => BooleanExpression::Conditional(s),
+            ConditionalOrExpression::Expression(u) => u,
         },
         BooleanExpression::Select(select) => match f.fold_select_expression(&Type::Boolean, select)
         {
@@ -922,9 +924,9 @@ pub fn fold_uint_expression_inner<'ast, T: Field, F: Folder<'ast, T>>(
             SelectOrExpression::Select(s) => UExpressionInner::Select(s),
             SelectOrExpression::Expression(u) => u,
         },
-        UExpressionInner::IfElse(c) => match f.fold_if_else_expression(&ty, c) {
-            IfElseOrExpression::IfElse(s) => UExpressionInner::IfElse(s),
-            IfElseOrExpression::Expression(u) => u,
+        UExpressionInner::Conditional(c) => match f.fold_conditional_expression(&ty, c) {
+            ConditionalOrExpression::Conditional(s) => UExpressionInner::Conditional(s),
+            ConditionalOrExpression::Expression(u) => u,
         },
         UExpressionInner::Member(m) => match f.fold_member_expression(&ty, m) {
             MemberOrExpression::Member(m) => UExpressionInner::Member(m),

zokrates_core/src/typed_absy/integer.rs

@@ -5,9 +5,10 @@ use crate::typed_absy::types::{
 };
 use crate::typed_absy::UBitwidth;
 use crate::typed_absy::{
-    ArrayExpression, ArrayExpressionInner, BooleanExpression, Expr, FieldElementExpression, IfElse,
-    IfElseExpression, Select, SelectExpression, StructExpression, StructExpressionInner, Typed,
-    TypedExpression, TypedExpressionOrSpread, TypedSpread, UExpression, UExpressionInner,
+    ArrayExpression, ArrayExpressionInner, BooleanExpression, Conditional, ConditionalExpression,
+    Expr, FieldElementExpression, Select, SelectExpression, StructExpression,
+    StructExpressionInner, Typed, TypedExpression, TypedExpressionOrSpread, TypedSpread,
+    UExpression, UExpressionInner,
 };
 use num_bigint::BigUint;
 use std::convert::TryFrom;
@@ -239,7 +240,7 @@ pub enum IntExpression<'ast, T> {
     Div(Box<IntExpression<'ast, T>>, Box<IntExpression<'ast, T>>),
     Rem(Box<IntExpression<'ast, T>>, Box<IntExpression<'ast, T>>),
     Pow(Box<IntExpression<'ast, T>>, Box<IntExpression<'ast, T>>),
-    IfElse(IfElseExpression<'ast, T, IntExpression<'ast, T>>),
+    Conditional(ConditionalExpression<'ast, T, IntExpression<'ast, T>>),
     Select(SelectExpression<'ast, T, IntExpression<'ast, T>>),
     Xor(Box<IntExpression<'ast, T>>, Box<IntExpression<'ast, T>>),
     And(Box<IntExpression<'ast, T>>, Box<IntExpression<'ast, T>>),
@@ -354,7 +355,7 @@ impl<'ast, T: fmt::Display> fmt::Display for IntExpression<'ast, T> {
             IntExpression::RightShift(ref e, ref by) => write!(f, "({} >> {})", e, by),
             IntExpression::LeftShift(ref e, ref by) => write!(f, "({} << {})", e, by),
             IntExpression::Not(ref e) => write!(f, "!{}", e),
-            IntExpression::IfElse(ref c) => write!(f, "{}", c),
+            IntExpression::Conditional(ref c) => write!(f, "{}", c),
         }
     }
 }
@@ -404,10 +405,11 @@ impl<'ast, T: Field> FieldElementExpression<'ast, T> {
             )),
             IntExpression::Pos(box e) => Ok(Self::Pos(box Self::try_from_int(e)?)),
             IntExpression::Neg(box e) => Ok(Self::Neg(box Self::try_from_int(e)?)),
-            IntExpression::IfElse(c) => Ok(Self::IfElse(IfElseExpression::new(
+            IntExpression::Conditional(c) => Ok(Self::Conditional(ConditionalExpression::new(
                 *c.condition,
                 Self::try_from_int(*c.consequence)?,
                 Self::try_from_int(*c.alternative)?,
+                c.kind,
             ))),
             IntExpression::Select(select) => {
                 let array = *select.array;
@@ -523,10 +525,11 @@ impl<'ast, T: Field> UExpression<'ast, T> {
                 Self::try_from_int(e1, bitwidth)?,
                 e2,
             )),
-            IfElse(c) => Ok(UExpression::if_else(
+            Conditional(c) => Ok(UExpression::conditional(
                 *c.condition,
                 Self::try_from_int(*c.consequence, bitwidth)?,
                 Self::try_from_int(*c.alternative, bitwidth)?,
+                c.kind,
             )),
             Select(select) => {
                 let array = *select.array;
@@ -693,6 +696,7 @@ impl<'ast, T> From<BigUint> for IntExpression<'ast, T> {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::typed_absy::ConditionalKind;
     use zokrates_field::Bn128Field;
 
     #[test]
@@ -714,7 +718,7 @@ mod tests {
             n.clone() * n.clone(),
             IntExpression::pow(n.clone(), n.clone()),
             n.clone() / n.clone(),
-            IntExpression::if_else(c.clone(), n.clone(), n.clone()),
+            IntExpression::conditional(c.clone(), n.clone(), n.clone(), ConditionalKind::IfElse),
             IntExpression::select(n_a.clone(), i.clone()),
         ];
 
@@ -725,7 +729,12 @@ mod tests {
             t.clone() * t.clone(),
             FieldElementExpression::pow(t.clone(), i.clone()),
             t.clone() / t.clone(),
-            FieldElementExpression::if_else(c.clone(), t.clone(), t.clone()),
+            FieldElementExpression::conditional(
+                c.clone(),
+                t.clone(),
+                t.clone(),
+                ConditionalKind::IfElse,
+            ),
             FieldElementExpression::select(t_a.clone(), i.clone()),
         ];
 
@@ -780,7 +789,7 @@ mod tests {
             IntExpression::left_shift(n.clone(), i.clone()),
             IntExpression::right_shift(n.clone(), i.clone()),
             !n.clone(),
-            IntExpression::if_else(c.clone(), n.clone(), n.clone()),
+            IntExpression::conditional(c.clone(), n.clone(), n.clone(), ConditionalKind::IfElse),
             IntExpression::select(n_a.clone(), i.clone()),
         ];
 
@@ -797,7 +806,7 @@ mod tests {
             UExpression::left_shift(t.clone(), i.clone()),
             UExpression::right_shift(t.clone(), i.clone()),
             !t.clone(),
-            UExpression::if_else(c.clone(), t.clone(), t.clone()),
+            UExpression::conditional(c.clone(), t.clone(), t.clone(), ConditionalKind::IfElse),
             UExpression::select(t_a.clone(), i.clone()),
         ];
 

zokrates_core/src/typed_absy/mod.rs

@@ -792,7 +792,7 @@ impl<'ast, T: fmt::Display> fmt::Display for StructExpression<'ast, T> {
             StructExpressionInner::FunctionCall(ref function_call) => {
                 write!(f, "{}", function_call)
             }
-            StructExpressionInner::IfElse(ref c) => write!(f, "{}", c),
+            StructExpressionInner::Conditional(ref c) => write!(f, "{}", c),
             StructExpressionInner::Member(ref m) => write!(f, "{}", m),
             StructExpressionInner::Select(ref select) => write!(f, "{}", select),
         }
@@ -937,30 +937,50 @@ impl<'ast, T: fmt::Display, E> fmt::Display for SelectExpression<'ast, T, E> {
     }
 }
 
-#[derive(Clone, PartialEq, Debug, Hash, Eq, PartialOrd, Ord)]
-pub struct IfElseExpression<'ast, T, E> {
+#[derive(Debug, Clone, PartialEq, Hash, Eq, PartialOrd, Ord)]
+pub enum ConditionalKind {
+    IfElse,
+    Ternary,
+}
+
+#[derive(Debug, Clone, PartialEq, Hash, Eq, PartialOrd, Ord)]
+pub struct ConditionalExpression<'ast, T, E> {
     pub condition: Box<BooleanExpression<'ast, T>>,
     pub consequence: Box<E>,
     pub alternative: Box<E>,
+    pub kind: ConditionalKind,
 }
 
-impl<'ast, T, E> IfElseExpression<'ast, T, E> {
-    pub fn new(condition: BooleanExpression<'ast, T>, consequence: E, alternative: E) -> Self {
-        IfElseExpression {
+impl<'ast, T, E> ConditionalExpression<'ast, T, E> {
+    pub fn new(
+        condition: BooleanExpression<'ast, T>,
+        consequence: E,
+        alternative: E,
+        kind: ConditionalKind,
+    ) -> Self {
+        ConditionalExpression {
             condition: box condition,
             consequence: box consequence,
             alternative: box alternative,
+            kind,
         }
     }
 }
 
-impl<'ast, T: fmt::Display, E: fmt::Display> fmt::Display for IfElseExpression<'ast, T, E> {
+impl<'ast, T: fmt::Display, E: fmt::Display> fmt::Display for ConditionalExpression<'ast, T, E> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(
-            f,
-            "if {} then {} else {} fi",
-            self.condition, self.consequence, self.alternative
-        )
+        match self.kind {
+            ConditionalKind::IfElse => write!(
+                f,
+                "if {} then {} else {} fi",
+                self.condition, self.consequence, self.alternative
+            ),
+            ConditionalKind::Ternary => write!(
+                f,
+                "{} ? {} : {}",
+                self.condition, self.consequence, self.alternative
+            ),
+        }
     }
 }
 
@@ -1042,7 +1062,7 @@ pub enum FieldElementExpression<'ast, T> {
         Box<FieldElementExpression<'ast, T>>,
         Box<UExpression<'ast, T>>,
     ),
-    IfElse(IfElseExpression<'ast, T, Self>),
+    Conditional(ConditionalExpression<'ast, T, Self>),
     Neg(Box<FieldElementExpression<'ast, T>>),
     Pos(Box<FieldElementExpression<'ast, T>>),
     FunctionCall(FunctionCallExpression<'ast, T, Self>),
@@ -1142,7 +1162,7 @@ pub enum BooleanExpression<'ast, T> {
         Box<BooleanExpression<'ast, T>>,
     ),
     Not(Box<BooleanExpression<'ast, T>>),
-    IfElse(IfElseExpression<'ast, T, Self>),
+    Conditional(ConditionalExpression<'ast, T, Self>),
     Member(MemberExpression<'ast, T, Self>),
     FunctionCall(FunctionCallExpression<'ast, T, Self>),
     Select(SelectExpression<'ast, T, Self>),
@@ -1249,7 +1269,7 @@ pub enum ArrayExpressionInner<'ast, T> {
     Identifier(Identifier<'ast>),
     Value(ArrayValue<'ast, T>),
     FunctionCall(FunctionCallExpression<'ast, T, ArrayExpression<'ast, T>>),
-    IfElse(IfElseExpression<'ast, T, ArrayExpression<'ast, T>>),
+    Conditional(ConditionalExpression<'ast, T, ArrayExpression<'ast, T>>),
     Member(MemberExpression<'ast, T, ArrayExpression<'ast, T>>),
     Select(SelectExpression<'ast, T, ArrayExpression<'ast, T>>),
     Slice(
@@ -1313,7 +1333,7 @@ pub enum StructExpressionInner<'ast, T> {
     Identifier(Identifier<'ast>),
     Value(Vec<TypedExpression<'ast, T>>),
     FunctionCall(FunctionCallExpression<'ast, T, StructExpression<'ast, T>>),
-    IfElse(IfElseExpression<'ast, T, StructExpression<'ast, T>>),
+    Conditional(ConditionalExpression<'ast, T, StructExpression<'ast, T>>),
     Member(MemberExpression<'ast, T, StructExpression<'ast, T>>),
     Select(SelectExpression<'ast, T, StructExpression<'ast, T>>),
 }
@@ -1455,7 +1475,7 @@ impl<'ast, T: fmt::Display> fmt::Display for FieldElementExpression<'ast, T> {
             FieldElementExpression::Pow(ref lhs, ref rhs) => write!(f, "{}**{}", lhs, rhs),
             FieldElementExpression::Neg(ref e) => write!(f, "(-{})", e),
             FieldElementExpression::Pos(ref e) => write!(f, "(+{})", e),
-            FieldElementExpression::IfElse(ref c) => write!(f, "{}", c),
+            FieldElementExpression::Conditional(ref c) => write!(f, "{}", c),
             FieldElementExpression::FunctionCall(ref function_call) => {
                 write!(f, "{}", function_call)
             }
@@ -1489,7 +1509,7 @@ impl<'ast, T: fmt::Display> fmt::Display for UExpression<'ast, T> {
             UExpressionInner::Pos(ref e) => write!(f, "(+{})", e),
             UExpressionInner::Select(ref select) => write!(f, "{}", select),
             UExpressionInner::FunctionCall(ref function_call) => write!(f, "{}", function_call),
-            UExpressionInner::IfElse(ref c) => write!(f, "{}", c),
+            UExpressionInner::Conditional(ref c) => write!(f, "{}", c),
             UExpressionInner::Member(ref m) => write!(f, "{}", m),
         }
     }
@@ -1518,7 +1538,7 @@ impl<'ast, T: fmt::Display> fmt::Display for BooleanExpression<'ast, T> {
             BooleanExpression::Not(ref exp) => write!(f, "!{}", exp),
             BooleanExpression::Value(b) => write!(f, "{}", b),
             BooleanExpression::FunctionCall(ref function_call) => write!(f, "{}", function_call),
-            BooleanExpression::IfElse(ref c) => write!(f, "{}", c),
+            BooleanExpression::Conditional(ref c) => write!(f, "{}", c),
             BooleanExpression::Member(ref m) => write!(f, "{}", m),
             BooleanExpression::Select(ref select) => write!(f, "{}", select),
         }
@@ -1540,7 +1560,7 @@ impl<'ast, T: fmt::Display> fmt::Display for ArrayExpressionInner<'ast, T> {
                     .join(", ")
             ),
             ArrayExpressionInner::FunctionCall(ref function_call) => write!(f, "{}", function_call),
-            ArrayExpressionInner::IfElse(ref c) => write!(f, "{}", c),
+            ArrayExpressionInner::Conditional(ref c) => write!(f, "{}", c),
             ArrayExpressionInner::Member(ref m) => write!(f, "{}", m),
             ArrayExpressionInner::Select(ref select) => write!(f, "{}", select),
             ArrayExpressionInner::Slice(ref a, ref from, ref to) => {
@@ -1780,81 +1800,121 @@ pub enum MemberOrExpression<'ast, T, E: Expr<'ast, T>> {
     Expression(E::Inner),
 }
 
-pub enum IfElseOrExpression<'ast, T, E: Expr<'ast, T>> {
-    IfElse(IfElseExpression<'ast, T, E>),
+pub enum ConditionalOrExpression<'ast, T, E: Expr<'ast, T>> {
+    Conditional(ConditionalExpression<'ast, T, E>),
     Expression(E::Inner),
 }
 
-pub trait IfElse<'ast, T> {
-    fn if_else(condition: BooleanExpression<'ast, T>, consequence: Self, alternative: Self)
-        -> Self;
-}
-
-impl<'ast, T> IfElse<'ast, T> for FieldElementExpression<'ast, T> {
-    fn if_else(
+pub trait Conditional<'ast, T> {
+    fn conditional(
         condition: BooleanExpression<'ast, T>,
         consequence: Self,
         alternative: Self,
+        kind: ConditionalKind,
+    ) -> Self;
+}
+
+impl<'ast, T> Conditional<'ast, T> for FieldElementExpression<'ast, T> {
+    fn conditional(
+        condition: BooleanExpression<'ast, T>,
+        consequence: Self,
+        alternative: Self,
+        kind: ConditionalKind,
     ) -> Self {
-        FieldElementExpression::IfElse(IfElseExpression::new(condition, consequence, alternative))
+        FieldElementExpression::Conditional(ConditionalExpression::new(
+            condition,
+            consequence,
+            alternative,
+            kind,
+        ))
     }
 }
 
-impl<'ast, T> IfElse<'ast, T> for IntExpression<'ast, T> {
-    fn if_else(
+impl<'ast, T> Conditional<'ast, T> for IntExpression<'ast, T> {
+    fn conditional(
         condition: BooleanExpression<'ast, T>,
         consequence: Self,
         alternative: Self,
+        kind: ConditionalKind,
     ) -> Self {
-        IntExpression::IfElse(IfElseExpression::new(condition, consequence, alternative))
+        IntExpression::Conditional(ConditionalExpression::new(
+            condition,
+            consequence,
+            alternative,
+            kind,
+        ))
     }
 }
 
-impl<'ast, T> IfElse<'ast, T> for BooleanExpression<'ast, T> {
-    fn if_else(
+impl<'ast, T> Conditional<'ast, T> for BooleanExpression<'ast, T> {
+    fn conditional(
         condition: BooleanExpression<'ast, T>,
         consequence: Self,
         alternative: Self,
+        kind: ConditionalKind,
     ) -> Self {
-        BooleanExpression::IfElse(IfElseExpression::new(condition, consequence, alternative))
+        BooleanExpression::Conditional(ConditionalExpression::new(
+            condition,
+            consequence,
+            alternative,
+            kind,
+        ))
     }
 }
 
-impl<'ast, T> IfElse<'ast, T> for UExpression<'ast, T> {
-    fn if_else(
+impl<'ast, T> Conditional<'ast, T> for UExpression<'ast, T> {
+    fn conditional(
         condition: BooleanExpression<'ast, T>,
         consequence: Self,
         alternative: Self,
+        kind: ConditionalKind,
     ) -> Self {
         let bitwidth = consequence.bitwidth;
 
-        UExpressionInner::IfElse(IfElseExpression::new(condition, consequence, alternative))
-            .annotate(bitwidth)
+        UExpressionInner::Conditional(ConditionalExpression::new(
+            condition,
+            consequence,
+            alternative,
+            kind,
+        ))
+        .annotate(bitwidth)
     }
 }
 
-impl<'ast, T: Clone> IfElse<'ast, T> for ArrayExpression<'ast, T> {
-    fn if_else(
+impl<'ast, T: Clone> Conditional<'ast, T> for ArrayExpression<'ast, T> {
+    fn conditional(
         condition: BooleanExpression<'ast, T>,
         consequence: Self,
         alternative: Self,
+        kind: ConditionalKind,
     ) -> Self {
         let ty = consequence.inner_type().clone();
         let size = consequence.size();
-        ArrayExpressionInner::IfElse(IfElseExpression::new(condition, consequence, alternative))
-            .annotate(ty, size)
+        ArrayExpressionInner::Conditional(ConditionalExpression::new(
+            condition,
+            consequence,
+            alternative,
+            kind,
+        ))
+        .annotate(ty, size)
     }
 }
 
-impl<'ast, T: Clone> IfElse<'ast, T> for StructExpression<'ast, T> {
-    fn if_else(
+impl<'ast, T: Clone> Conditional<'ast, T> for StructExpression<'ast, T> {
+    fn conditional(
         condition: BooleanExpression<'ast, T>,
         consequence: Self,
         alternative: Self,
+        kind: ConditionalKind,
     ) -> Self {
         let ty = consequence.ty().clone();
-        StructExpressionInner::IfElse(IfElseExpression::new(condition, consequence, alternative))
-            .annotate(ty)
+        StructExpressionInner::Conditional(ConditionalExpression::new(
+            condition,
+            consequence,
+            alternative,
+            kind,
+        ))
+        .annotate(ty)
     }
 }
 

zokrates_core/src/typed_absy/result_folder.rs

@@ -184,14 +184,14 @@ pub trait ResultFolder<'ast, T: Field>: Sized {
         fold_types(self, tys)
     }
 
-    fn fold_if_else_expression<
-        E: Expr<'ast, T> + PartialEq + IfElse<'ast, T> + ResultFold<'ast, T>,
+    fn fold_conditional_expression<
+        E: Expr<'ast, T> + PartialEq + Conditional<'ast, T> + ResultFold<'ast, T>,
     >(
         &mut self,
         ty: &E::Ty,
-        e: IfElseExpression<'ast, T, E>,
-    ) -> Result<IfElseOrExpression<'ast, T, E>, Self::Error> {
-        fold_if_else_expression(self, ty, e)
+        e: ConditionalExpression<'ast, T, E>,
+    ) -> Result<ConditionalOrExpression<'ast, T, E>, Self::Error> {
+        fold_conditional_expression(self, ty, e)
     }
 
     fn fold_block_expression<E: ResultFold<'ast, T>>(
@@ -507,9 +507,9 @@ pub fn fold_array_expression_inner<'ast, T: Field, F: ResultFolder<'ast, T>>(
                 FunctionCallOrExpression::Expression(u) => u,
             }
         }
-        ArrayExpressionInner::IfElse(c) => match f.fold_if_else_expression(ty, c)? {
-            IfElseOrExpression::IfElse(c) => ArrayExpressionInner::IfElse(c),
-            IfElseOrExpression::Expression(u) => u,
+        ArrayExpressionInner::Conditional(c) => match f.fold_conditional_expression(ty, c)? {
+            ConditionalOrExpression::Conditional(c) => ArrayExpressionInner::Conditional(c),
+            ConditionalOrExpression::Expression(u) => u,
         },
         ArrayExpressionInner::Member(m) => match f.fold_member_expression(ty, m)? {
             MemberOrExpression::Member(m) => ArrayExpressionInner::Member(m),
@@ -572,9 +572,9 @@ pub fn fold_struct_expression_inner<'ast, T: Field, F: ResultFolder<'ast, T>>(
                 FunctionCallOrExpression::Expression(u) => u,
             }
         }
-        StructExpressionInner::IfElse(c) => match f.fold_if_else_expression(ty, c)? {
-            IfElseOrExpression::IfElse(c) => StructExpressionInner::IfElse(c),
-            IfElseOrExpression::Expression(u) => u,
+        StructExpressionInner::Conditional(c) => match f.fold_conditional_expression(ty, c)? {
+            ConditionalOrExpression::Conditional(c) => StructExpressionInner::Conditional(c),
+            ConditionalOrExpression::Expression(u) => u,
         },
         StructExpressionInner::Member(m) => match f.fold_member_expression(ty, m)? {
             MemberOrExpression::Member(m) => StructExpressionInner::Member(m),
@@ -635,10 +635,10 @@ pub fn fold_field_expression<'ast, T: Field, F: ResultFolder<'ast, T>>(
 
             FieldElementExpression::Pos(box e)
         }
-        FieldElementExpression::IfElse(c) => {
-            match f.fold_if_else_expression(&Type::FieldElement, c)? {
-                IfElseOrExpression::IfElse(c) => FieldElementExpression::IfElse(c),
-                IfElseOrExpression::Expression(u) => u,
+        FieldElementExpression::Conditional(c) => {
+            match f.fold_conditional_expression(&Type::FieldElement, c)? {
+                ConditionalOrExpression::Conditional(c) => FieldElementExpression::Conditional(c),
+                ConditionalOrExpression::Expression(u) => u,
             }
         }
         FieldElementExpression::FunctionCall(function_call) => {
@@ -689,11 +689,11 @@ pub fn fold_block_expression<'ast, T: Field, E: ResultFold<'ast, T>, F: ResultFo
     })
 }
 
-pub fn fold_if_else_expression<
+pub fn fold_conditional_expression<
     'ast,
     T: Field,
     E: Expr<'ast, T>
-        + IfElse<'ast, T>
+        + Conditional<'ast, T>
         + PartialEq
         + ResultFold<'ast, T>
         + From<TypedExpression<'ast, T>>,
@@ -701,13 +701,16 @@ pub fn fold_if_else_expression<
 >(
     f: &mut F,
     _: &E::Ty,
-    e: IfElseExpression<'ast, T, E>,
-) -> Result<IfElseOrExpression<'ast, T, E>, F::Error> {
-    Ok(IfElseOrExpression::IfElse(IfElseExpression::new(
-        f.fold_boolean_expression(*e.condition)?,
-        e.consequence.fold(f)?,
-        e.alternative.fold(f)?,
-    )))
+    e: ConditionalExpression<'ast, T, E>,
+) -> Result<ConditionalOrExpression<'ast, T, E>, F::Error> {
+    Ok(ConditionalOrExpression::Conditional(
+        ConditionalExpression::new(
+            f.fold_boolean_expression(*e.condition)?,
+            e.consequence.fold(f)?,
+            e.alternative.fold(f)?,
+            e.kind,
+        ),
+    ))
 }
 
 pub fn fold_member_expression<
@@ -863,10 +866,12 @@ pub fn fold_boolean_expression<'ast, T: Field, F: ResultFolder<'ast, T>>(
                 FunctionCallOrExpression::Expression(u) => u,
             }
         }
-        BooleanExpression::IfElse(c) => match f.fold_if_else_expression(&Type::Boolean, c)? {
-            IfElseOrExpression::IfElse(c) => BooleanExpression::IfElse(c),
-            IfElseOrExpression::Expression(u) => u,
-        },
+        BooleanExpression::Conditional(c) => {
+            match f.fold_conditional_expression(&Type::Boolean, c)? {
+                ConditionalOrExpression::Conditional(c) => BooleanExpression::Conditional(c),
+                ConditionalOrExpression::Expression(u) => u,
+            }
+        }
         BooleanExpression::Select(select) => {
             match f.fold_select_expression(&Type::Boolean, select)? {
                 SelectOrExpression::Select(s) => BooleanExpression::Select(s),
@@ -991,9 +996,9 @@ pub fn fold_uint_expression_inner<'ast, T: Field, F: ResultFolder<'ast, T>>(
             SelectOrExpression::Select(s) => UExpressionInner::Select(s),
             SelectOrExpression::Expression(u) => u,
         },
-        UExpressionInner::IfElse(c) => match f.fold_if_else_expression(&ty, c)? {
-            IfElseOrExpression::IfElse(c) => UExpressionInner::IfElse(c),
-            IfElseOrExpression::Expression(u) => u,
+        UExpressionInner::Conditional(c) => match f.fold_conditional_expression(&ty, c)? {
+            ConditionalOrExpression::Conditional(c) => UExpressionInner::Conditional(c),
+            ConditionalOrExpression::Expression(u) => u,
         },
         UExpressionInner::Member(m) => match f.fold_member_expression(&ty, m)? {
             MemberOrExpression::Member(m) => UExpressionInner::Member(m),

zokrates_core/src/typed_absy/uint.rs

@@ -193,7 +193,7 @@ pub enum UExpressionInner<'ast, T> {
     FunctionCall(FunctionCallExpression<'ast, T, UExpression<'ast, T>>),
     LeftShift(Box<UExpression<'ast, T>>, Box<UExpression<'ast, T>>),
     RightShift(Box<UExpression<'ast, T>>, Box<UExpression<'ast, T>>),
-    IfElse(IfElseExpression<'ast, T, UExpression<'ast, T>>),
+    Conditional(ConditionalExpression<'ast, T, UExpression<'ast, T>>),
     Member(MemberExpression<'ast, T, UExpression<'ast, T>>),
     Select(SelectExpression<'ast, T, UExpression<'ast, T>>),
 }

zokrates_core_test/tests/tests/ternary.json

@@ -0,0 +1,36 @@
+{
+  "entry_point": "./tests/tests/ternary.zok",
+  "max_constraint_count": 6,
+  "tests": [
+    {
+      "input": {
+        "values": ["1", "0"]
+      },
+      "output": {
+        "Ok": {
+          "values": ["1"]
+        }
+      }
+    },
+    {
+      "input": {
+        "values": ["0", "1"]
+      },
+      "output": {
+        "Ok": {
+          "values": ["2"]
+        }
+      }
+    },
+    {
+      "input": {
+        "values": ["0", "0"]
+      },
+      "output": {
+        "Ok": {
+          "values": ["3"]
+        }
+      }
+    }
+  ]
+}

zokrates_core_test/tests/tests/ternary.zok

@@ -0,0 +1,5 @@
+def main(bool a, bool b) -> field:
+    field x = a ? 1 : b ? 2 : 3 // (a ? 1 : (b ? 2 : 3))
+    field y = if a then 1 else if b then 2 else 3 fi fi
+    assert(x == y)
+    return x

zokrates_parser/src/zokrates.pest

@@ -68,13 +68,13 @@ expression = { unaried_term ~ (op_binary ~ unaried_term)* }
 unaried_term = { op_unary? ~ powered_term }
 powered_term = { postfixed_term ~ (op_pow ~ exponent_expression)? }
 postfixed_term = { term ~ access* }
-term = { ("(" ~ expression ~ ")") | inline_struct_expression | conditional_expression | primary_expression | inline_array_expression | array_initializer_expression }
+term = { ("(" ~ expression ~ ")") | inline_struct_expression | if_else_expression | primary_expression | inline_array_expression | array_initializer_expression }
 spread = { "..." ~ expression }
 range = { from_expression? ~ ".." ~ to_expression? }
 from_expression = { expression }
 to_expression = { expression }
 
-conditional_expression = { "if" ~ expression ~ "then" ~ expression ~ "else" ~ expression ~ "fi"}
+if_else_expression = { "if" ~ expression ~ "then" ~ expression ~ "else" ~ expression ~ "fi"}
 
 access = { array_access | call_access | member_access }
 array_access = { "[" ~ range_or_expression ~ "]" }
@@ -155,8 +155,10 @@ op_neg = {"-"}
 op_pos = {"+"}
 op_left_shift = @{"<<"}
 op_right_shift = @{">>"}
+op_ternary = {"?" ~ expression ~ ":"}
+
 // `op_pow` is *not* in `op_binary` because its precedence is handled in this parser rather than down the line in precedence climbing
-op_binary = _ { op_or | op_and | op_bit_xor | op_bit_and | op_bit_or | op_left_shift | op_right_shift | op_equal | op_not_equal | op_lte | op_lt | op_gte | op_gt | op_add | op_sub | op_mul | op_div | op_rem }
+op_binary = _ { op_or | op_and | op_bit_xor | op_bit_and | op_bit_or | op_left_shift | op_right_shift | op_equal | op_not_equal | op_lte | op_lt | op_gte | op_gt | op_add | op_sub | op_mul | op_div | op_rem | op_ternary }
 op_unary = { op_pos | op_neg | op_not }
 
 WHITESPACE = _{ " " | "\t" | "\\" ~ COMMENT? ~ NEWLINE}

zokrates_pest_ast/src/lib.rs

@@ -13,7 +13,7 @@ pub use ast::{
     CallAccess, ConstantDefinition, ConstantGenericValue, DecimalLiteralExpression, DecimalNumber,
     DecimalSuffix, DefinitionStatement, ExplicitGenerics, Expression, FieldType, File,
     FromExpression, FunctionDefinition, HexLiteralExpression, HexNumberExpression,
-    IdentifierExpression, ImportDirective, ImportSymbol, InlineArrayExpression,
+    IdentifierExpression, IfElseExpression, ImportDirective, ImportSymbol, InlineArrayExpression,
     InlineStructExpression, InlineStructMember, IterationStatement, LiteralExpression, Parameter,
     PostfixExpression, Range, RangeOrExpression, ReturnStatement, Span, Spread, SpreadOrExpression,
     Statement, StructDefinition, StructField, SymbolDeclaration, TernaryExpression, ToExpression,
@@ -38,6 +38,7 @@ mod ast {
     // based on https://docs.python.org/3/reference/expressions.html#operator-precedence
     fn build_precedence_climber() -> PrecClimber<Rule> {
         PrecClimber::new(vec![
+            Operator::new(Rule::op_ternary, Assoc::Right),
             Operator::new(Rule::op_or, Assoc::Left),
             Operator::new(Rule::op_and, Assoc::Left),
             Operator::new(Rule::op_lt, Assoc::Left)
@@ -89,6 +90,12 @@ mod ast {
             Rule::op_bit_or => Expression::binary(BinaryOperator::BitOr, lhs, rhs, span),
             Rule::op_right_shift => Expression::binary(BinaryOperator::RightShift, lhs, rhs, span),
             Rule::op_left_shift => Expression::binary(BinaryOperator::LeftShift, lhs, rhs, span),
+            Rule::op_ternary => Expression::ternary(
+                lhs,
+                Box::new(Expression::from_pest(&mut pair.into_inner()).unwrap()),
+                rhs,
+                span,
+            ),
             _ => unreachable!(),
         })
     }
@@ -412,6 +419,7 @@ mod ast {
     #[derive(Debug, PartialEq, Clone)]
     pub enum Expression<'ast> {
         Ternary(TernaryExpression<'ast>),
+        IfElse(IfElseExpression<'ast>),
         Binary(BinaryExpression<'ast>),
         Unary(UnaryExpression<'ast>),
         Postfix(PostfixExpression<'ast>),
@@ -427,7 +435,7 @@ mod ast {
     pub enum Term<'ast> {
         Expression(Expression<'ast>),
         InlineStruct(InlineStructExpression<'ast>),
-        Ternary(TernaryExpression<'ast>),
+        IfElse(IfElseExpression<'ast>),
         Primary(PrimaryExpression<'ast>),
         InlineArray(InlineArrayExpression<'ast>),
         ArrayInitializer(ArrayInitializerExpression<'ast>),
@@ -543,7 +551,7 @@ mod ast {
         fn from(t: Term<'ast>) -> Self {
             match t {
                 Term::Expression(e) => e,
-                Term::Ternary(e) => Expression::Ternary(e),
+                Term::IfElse(e) => Expression::IfElse(e),
                 Term::Primary(e) => e.into(),
                 Term::InlineArray(e) => Expression::InlineArray(e),
                 Term::InlineStruct(e) => Expression::InlineStruct(e),
@@ -761,27 +769,49 @@ mod ast {
         pub span: Span<'ast>,
     }
 
-    #[derive(Debug, FromPest, PartialEq, Clone)]
-    #[pest_ast(rule(Rule::conditional_expression))]
+    #[derive(Debug, PartialEq, Clone)]
     pub struct TernaryExpression<'ast> {
-        pub first: Box<Expression<'ast>>,
-        pub second: Box<Expression<'ast>>,
-        pub third: Box<Expression<'ast>>,
+        pub condition: Box<Expression<'ast>>,
+        pub consequence: Box<Expression<'ast>>,
+        pub alternative: Box<Expression<'ast>>,
+        pub span: Span<'ast>,
+    }
+
+    #[derive(Debug, FromPest, PartialEq, Clone)]
+    #[pest_ast(rule(Rule::if_else_expression))]
+    pub struct IfElseExpression<'ast> {
+        pub condition: Box<Expression<'ast>>,
+        pub consequence: Box<Expression<'ast>>,
+        pub alternative: Box<Expression<'ast>>,
         #[pest_ast(outer())]
         pub span: Span<'ast>,
     }
 
     impl<'ast> Expression<'ast> {
+        pub fn if_else(
+            condition: Box<Expression<'ast>>,
+            consequence: Box<Expression<'ast>>,
+            alternative: Box<Expression<'ast>>,
+            span: Span<'ast>,
+        ) -> Self {
+            Expression::IfElse(IfElseExpression {
+                condition,
+                consequence,
+                alternative,
+                span,
+            })
+        }
+
         pub fn ternary(
-            first: Box<Expression<'ast>>,
-            second: Box<Expression<'ast>>,
-            third: Box<Expression<'ast>>,
+            condition: Box<Expression<'ast>>,
+            consequence: Box<Expression<'ast>>,
+            alternative: Box<Expression<'ast>>,
             span: Span<'ast>,
         ) -> Self {
             Expression::Ternary(TernaryExpression {
-                first,
-                second,
-                third,
+                condition,
+                consequence,
+                alternative,
                 span,
             })
         }
@@ -806,6 +836,7 @@ mod ast {
                 Expression::Identifier(i) => &i.span,
                 Expression::Literal(c) => c.span(),
                 Expression::Ternary(t) => &t.span,
+                Expression::IfElse(ie) => &ie.span,
                 Expression::Postfix(p) => &p.span,
                 Expression::InlineArray(a) => &a.span,
                 Expression::InlineStruct(s) => &s.span,
@@ -1071,20 +1102,6 @@ mod tests {
         pub fn pow(left: Expression<'ast>, right: Expression<'ast>, span: Span<'ast>) -> Self {
             Self::binary(BinaryOperator::Pow, Box::new(left), Box::new(right), span)
         }
-
-        pub fn if_else(
-            condition: Expression<'ast>,
-            consequence: Expression<'ast>,
-            alternative: Expression<'ast>,
-            span: Span<'ast>,
-        ) -> Self {
-            Self::ternary(
-                Box::new(condition),
-                Box::new(consequence),
-                Box::new(alternative),
-                span,
-            )
-        }
     }
 
     #[test]
@@ -1263,7 +1280,7 @@ mod tests {
                         }))],
                         statements: vec![Statement::Return(ReturnStatement {
                             expressions: vec![Expression::if_else(
-                                Expression::Literal(LiteralExpression::DecimalLiteral(
+                                Box::new(Expression::Literal(LiteralExpression::DecimalLiteral(
                                     DecimalLiteralExpression {
                                         suffix: None,
                                         value: DecimalNumber {
@@ -1271,8 +1288,8 @@ mod tests {
                                         },
                                         span: Span::new(source, 62, 63).unwrap()
                                     }
-                                )),
-                                Expression::Literal(LiteralExpression::DecimalLiteral(
+                                ))),
+                                Box::new(Expression::Literal(LiteralExpression::DecimalLiteral(
                                     DecimalLiteralExpression {
                                         suffix: None,
                                         value: DecimalNumber {
@@ -1280,8 +1297,8 @@ mod tests {
                                         },
                                         span: Span::new(source, 69, 70).unwrap()
                                     }
-                                )),
-                                Expression::Literal(LiteralExpression::DecimalLiteral(
+                                ))),
+                                Box::new(Expression::Literal(LiteralExpression::DecimalLiteral(
                                     DecimalLiteralExpression {
                                         suffix: None,
                                         value: DecimalNumber {
@@ -1289,8 +1306,8 @@ mod tests {
                                         },
                                         span: Span::new(source, 76, 77).unwrap()
                                     }
-                                )),
-                                Span::new(source, 59, 80).unwrap()
+                                ))),
+                                Span::new(&source, 59, 80).unwrap()
                             )],
                             span: Span::new(source, 52, 80).unwrap(),
                         })],