From: Jim Pryor <profjim@jimpryor.net>
Date: Sat, 4 Dec 2010 23:31:41 +0000 (-0500)
Subject: translating tweaks
X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=8e24378981bd4095fe580475cf6a530e168965b1;ds=sidebyside

translating tweaks

Signed-off-by: Jim Pryor <profjim@jimpryor.net>
---

diff --git a/translating_between_OCaml_Scheme_and_Haskell.mdwn b/translating_between_OCaml_Scheme_and_Haskell.mdwn
index d0f7442c..b8938962 100644
--- a/translating_between_OCaml_Scheme_and_Haskell.mdwn
+++ b/translating_between_OCaml_Scheme_and_Haskell.mdwn
@@ -183,15 +183,17 @@ We will however try to give some general advice about how to translate between O
 		type Weight = Integer
 		type Person = (Name, Address)    -- supposing types Name and Address to be declared elsewhere
 
-	then you can use a value of type `Integer` wherever a `Weight` is expected, and vice versa. `newtype` and `data` on the other hand, create genuinely new types. `newtype` is basically just an efficient version of `data` that you can use in special circumstances. `newtype` must always take one type argument and have one value constructor. For example:
+	then you can use a value of type `Integer` wherever a `Weight` is expected, and vice versa. <!-- `type` is allowed to be parameterized -->
+
+	`newtype` and `data` on the other hand, create genuinely new types. `newtype` is basically just an efficient version of `data` that you can use in special circumstances. `newtype` must always take one type argument and have one value constructor. For example:
 
 		newtype PersonalData a = PD a
 
 	You could also say:
 
-		data PersonalData a = PD a
+		data PersonalData2 a = PD2 a
 
-	And `data` also allows multiple type arguments, and multiple variants and value constructors.
+	And `data` also allows multiple type arguments, and multiple variants and value constructors. <!-- Subtle difference: whereas `PersonalData a` is isomorphic to `a`, `PersonalData2 a` has an additional value, namely `PD2 _|_`. In a strict language, this is an additional type an expression can have, but it would not be a value. -->
 
 	OCaml just uses the one keyword `type` for all of these purposes:
 
@@ -201,7 +203,7 @@ We will however try to give some general advice about how to translate between O
 
 *	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
+		data PersonalData3 a = PersonalData3 a
 
 	The interpreter can always tell from the context when you're using the type name and when you're using the value constructor.