translating tweaks

[lambda.git] / translating_between_OCaml_Scheme_and_Haskell.mdwn

diff --git a/translating_between_OCaml_Scheme_and_Haskell.mdwn b/translating_between_OCaml_Scheme_and_Haskell.mdwn
index ed2ce4a..4b0f715 100644 (file)
--- a/translating_between_OCaml_Scheme_and_Haskell.mdwn
+++ b/translating_between_OCaml_Scheme_and_Haskell.mdwn
@@ -42,14 +42,17 @@ Additionally, the syntax of OCaml and SML is superficially much closer to Haskel
 
 *      **Type Variants and Pattern Matching** If you want to reproduce this kind of OCaml code:
 
-               type lambda_expression = Var of char | Lam of char * lambda_expression | App of lambda_expression * lambda_expression;;
+               # type lambda_expression = Var of char | Lam of char * lambda_expression | App of lambda_expression * lambda_expression;;
 
-               let rec free_vars (expr : lambda_expression) : char list =
+               # let rec free_vars (expr : lambda_expression) : char list =
                  match expr with
                    | Var label -> [label]
                    | Lam (label, body) -> remove label (free_vars body)
                    | App (left, right) -> merge (free_vars left) (free_vars right);;
 
+               # free_vars (Lam ('x', (App (Var 'x', Var 'y'))));;
+               - : char list = ['y']
+
        in Scheme, you have two choices. First, the quick hack:
 
                ; we use the symbols 'var and 'lam as tags, and assume
@@ -85,6 +88,8 @@ Additionally, the syntax of OCaml and SML is superficially much closer to Haskel
                    (lam (label body) (remove label (free-vars body)))
                    (app (left right) (remove-duplicates (append (free-vars left) (free-vars right))))))
 
+               (free-vars (lam 'x (app (var 'x) (var 'y))))
+               ; evaluates to '(y)
 
 *      Scheme has excellent support for working with implicit or "first-class" **continuations**, using either `call/cc` or any of various delimited continuation operators. See <http://docs.racket-lang.org/reference/cont.html?q=shift&q=do#%28part._.Classical_.Control_.Operators%29>.
 
@@ -145,7 +150,7 @@ We will however try to give some general advice about how to translate between O
 
 *      In Haskell, you say a value has a certain type with: `value :: type`. You express the operation of prepending a new `int` to a list of `int`s with `1 : other_numbers`. In OCaml it's the reverse: you say `value : type` and `1 :: other_numbers`.
 
-*      In Haskell, type names and constructors both begin with capital letters, and type variables always appear after their constructors, in Curried form. And the primary term for declaring a new type is `data` (short for [[!wikipedia algebraic datatype]]). So we have:
+*      In Haskell, type names and constructors both begin with capital letters, and type variables always appear after their constructors, in Curried form. And the primary term for declaring a new type is `data` (short for [[!wikipedia algebraic data type]]). So we have:
 
                data Either a b = Left a | Right b;
                data FooType a b = Foo_constructor1 a b | Foo_constructor2 a b;