X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=translating_between_OCaml_Scheme_and_Haskell.mdwn;h=4a4287a1e776a13524b7db78d2ef9de43fb83b00;hp=891490227c87c2b3ca7c3d567774d70f8bf74d33;hb=a7d3954c76604eea8d2c392c5eb2f9d11891460a;hpb=9e19c6911155ccdac50589b6f16e53a8953451b4

diff --git a/translating_between_OCaml_Scheme_and_Haskell.mdwn b/translating_between_OCaml_Scheme_and_Haskell.mdwn
index 89149022..4a4287a1 100644
--- 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
@@ -67,7 +70,7 @@ Additionally, the syntax of OCaml and SML is superficially much closer to Haskel
 
 	Second, you can create real datatypes and pattern-match on them. There are several tools for doing this. I'll describe the `define-datatype` and `cases` forms developed for the book *Essentials of Programming Languages* (EoPL) by Friedman and Wand.
 
-	(Alternatives include the `struct` form in Racket, see <http://docs.racket-lang.org/guide/define-struct.html>. Also `define-record-type` from srfi-9 and srfi-57; see also <http://docs.racket-lang.org/r6rs-lib-std/r6rs-lib-Z-H-7.html>.)
+	(Alternatives include [the `struct` form in Racket](http://docs.racket-lang.org/guide/define-struct.html). Also `define-record-type` from srfi-9 and srfi-57; see also [the r6rs libs](http://docs.racket-lang.org/r6rs-lib-std/r6rs-lib-Z-H-7.html).)
 
 	Here is how the tools from EoPL work. You must begin your file either with `#lang eopl` or with the first two lines below:
 
@@ -85,8 +88,10 @@ 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>.
+*	Scheme has excellent support for working with implicit or "first-class" **continuations**, using either `call/cc` or any of various delimited continuation operators. See [the Racket docs](http://docs.racket-lang.org/reference/cont.html?q=shift&q=do#%28part._.Classical_.Control_.Operators%29).
 
 	In Scheme you can use these forms by default (they're equivalent):
 
@@ -126,7 +131,8 @@ Additionally, the syntax of OCaml and SML is superficially much closer to Haskel
 
 	There is also a library for using *undelimited* continuations in OCaml, but it's shakier than Oleg's delimited continuation library.
 
-We won't say any more about translating to and from Scheme.
+There are some more hints about Scheme [here](/assignment8/) and [here](/week1/). We won't say any more here.
+
 
 
 #Haskell and OCaml#
@@ -145,8 +151,7 @@ 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 "abstract 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;
@@ -194,6 +199,12 @@ So we have:
 		type person = name * address;;
 		type 'a personal_data = PD of 'a;;
 
+*	When a type only has a single variant, as with PersonalData, Haskell programmers will often use the same name for both the type and the value constructor, like this:
+
+		data PersonalData a = PersonalData a
+
+	The interpreter can always tell from the context when you're using the type name and when you're using the value constructor.
+
 *	The type constructors discussed above took simple types as arguments. In Haskell, types are also allowed to take *type constructors* as arguments:
 
 		data BarType t = Bint (t Integer) | Bstring (t string)