Re: string/char vector type equivalence

On Tue, Feb 05, 2013 at 09:31:56AM -0500, Matthew Fluet wrote:
> I think that the reason that it doesn't is to support
> string constants, but I couldn't quickly see where the necessary type
> equalities were established in the Basis Library implementation and the
> type checker.

Actually, with some further experimentation, it seems like the fix should be
rather simple, as this does not compile:

	structure Vector :> sig
		eqtype 'a vector
		val fromList: 'a list -> 'a vector
	end = struct
		type 'a vector = 'a vector
		val fromList = vector
	end

	type 'a vector = 'a Vector.vector
	val vector = Vector.fromList

	val foo: char vector = "foo"
	val bar: string = vector [#"b", #"a", #"r"]
	val _ = foo ^ bar

	Error: opaquevector.sml 12.5.
	  Pattern and expression disagree.
	    pattern:    [char vector]
	    expression: [string]
	    in: (foo): char vector = "foo"
	Error: opaquevector.sml 13.5.
	  Pattern and expression disagree.
	    pattern:    [string]
	    expression: [char vector]
	    in: (bar): string = vector [#"b", #"a", #"r"]
	Error: opaquevector.sml 14.13.
	  Function applied to incorrect argument.
	    expects: [string] * _
	    but got: [char vector] * _
	    in: ^ (foo, bar)

Since there are no vector literals, it should be OK to do something
like this in the Basis Library without touching the type checker.

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