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Undecidability of OCaml type checking
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Date: 1999-07-14 (16:07)
From: John Skaller <skaller@m...>
Subject: Re: irritability of structure name conflicts
At 13:59 13/07/99 -0400, Dave Mason wrote:
>Is there some way I can force it to interpret the type constructor as
>a particular type so that it chooses the labels from the correct set?

This problem pervades ocaml. Another case of it is variants:

	type A = X | Y;
	type B = X | Z;

which all compiles fine, but then X is a constructor for
the B variant.

C also has the same problem with enumerations:

	enum X {a,b,c}; /* a,b,c are globals */

The problem can be solved, clumbsily, by wrapping inside a module.
(In C++, inside a class or namespace)

While I'm also expressing irritation, when I compile
a file (as opposed to using the interactive system);
rebinding of symbols shouldn't be allowed:

	let a = 1;;
	let a = 1.0;;
	print_int a;; 

	(* what does that strange type error mean! 
   	   a is an integer! It is right there at the top of the file!

Another similar case is 

	open List
	open Map
	iter ... 

Woops! I meant List.iter, not Map.iter :-)

There are several solutions, but the one that could
be implemented now with least impact would be to
issue warnings whenever a symbol is rebound
in the same scope during batch compilation.

(No warning in the interactive system; rebinding
to fix mistakes is common)

John Skaller    email:
		phone: 61-2-96600850
		snail: 10/1 Toxteth Rd, Glebe NSW 2037, Australia