Merge pull request #241 from Zokrates/variable-scope-doc

Document variable scope

zokrates_book/src/concepts/variables.md

@@ -1,4 +1,26 @@
 ## Variables
 
 Variables can have any name which does not start with a number. Underscores are not allowed in variable names.
-Variables are mutable, and always passed by values to functions.
+Variables are mutable, and always passed by value to functions.
+
+### Shadowing
+
+Shadowing is not allowed.
+```zokrates
+{{#include ../../../zokrates_cli/examples/book/no_shadowing.code}}
+```
+
+### Scope
+
+#### Function
+
+Functions have their own scope
+```zokrates
+{{#include ../../../zokrates_cli/examples/book/function_scope.code}}
+```
+
+#### For-loop
+For-loops have their own scope
+```zokrates
+{{#include ../../../zokrates_cli/examples/book/for_scope.code}}
+```

zokrates_cli/examples/book/for_scope.code

@@ -0,0 +1,7 @@
+def main() -> (field):
+	field a = 0
+	for field i in 0..5 do
+		a = a + i
+	endfor
+	// return i <- not allowed
+	return a

zokrates_cli/examples/book/function_scope.code

@@ -0,0 +1,7 @@
+def foo() -> (field):
+	// return myGlobal <- not allowed
+	return 42
+
+def main() -> (field):
+	field myGlobal = 42
+	return foo()

zokrates_cli/examples/book/no_shadowing.code

@@ -0,0 +1,7 @@
+def main() -> (field):
+	field a = 2
+	// field a = 3 <- not allowed
+	for field i in 0..5 do
+		// field a = 7 <- not allowed
+	endfor
+	return a

zokrates_cli/examples/error/out_of_for_scope.code

@@ -0,0 +1,4 @@
+def main() -> (field):
+	for field i in 0..5 do
+	endfor
+	return i

zokrates_cli/examples/error/shadowing.code

@@ -2,6 +2,6 @@ def foo() -> (field):
 	return 1
 
 def main() -> (field):
-	bool a
+	field a = 2
 	field a = foo()
 	return 1