grammar refactoring: build_visitor fixed & visitors tested

tests/functions.lang

@@ -1,7 +1,5 @@
-// "decl" is not required, but useful in module interface
-
 decl sum ('A : #Add) : 'A -> 'A -> 'A
-def sum : a b = a + b
+def sum 'A : a b = a + b
 
 decl fib : Int -> Int
 def fib : n =
@@ -16,25 +14,22 @@ def fact : n =
     | n -> n * fact (n - 1)
 
 decl find_prefix_hashes ('H : (#AccHash Char)) : String -> Array 'H
-def find_prefix_hashes ('H : (#AccHash Char)) : str = {
+def find_prefix_hashes 'H : str = {
   var hashes = (Array 'H).new (str.size + 1)
-  ; hashes.0 = 'H.of str.0
-   for i in 1..hashes.size do {
-     ; hashes.i = hashes.(i - 1).clone
-     ; hashes.i.append str.i
-   }
 
-   return hashes
+  ; hashes.0 = 'H.of str.0
+  for i in 1..hashes.size do {
+    ; hashes.i = hashes.(i - 1).clone
+    ; hashes.i.append str.i
+  }
+
+  return hashes
 }
 
-// ?? other default constructor symbol (instead of placeholder _), etc. ??
-
-// seporate first and last iteration of loop ?
-// previous and next iterations ?
+alias Hash = AccHash Char
 
 decl find_substring : String -> String -> Array Index
 def find_substring : str substr = {
-  alias Hash = AccHash Char
 
   var result = (Array Index).empty
 
@@ -64,7 +59,4 @@ decl mul : Int -> Int -> Int
 def mul : x y = x * y
 
 decl mul_10 : Int -> Int
-def mul_10 = mul 10 // or argument can be used
-
-// ?? is partial application feature needed ??
-
+def mul_10 = mul 10