Re: [Scheme-reports] Three really picky points

[Vincent Manis <vmanis@x>]

Two of my three picky points got some very good discussion. The third (actually the first one on my list) doesn't seem to have gotten any discussion, so I thought I'd raise it again. 

This refers to number syntax and pragmatics (I don't think there are semantics issues, we all ought to agree what a numeric representation means!). I couldn't find anywhere in the Draft that described the relation between numeric conversion in string->number, read, and in source programs, and was hoping for some kind of clarification (or a pointer to where I missed the clarification). 

The syntactic issues relate to such things as whether S, F, D, and L are valid (`the implementation *may* accept...', p. 32). Pragmatic issues include whether integer or other literals might overflow (on a bignumless implementation), whether or not the implementation applies the same restrictions, described at the bottom of p. 37) to string->number, read, and literals in source programs; the default precision if the E exponent marker is used; and numerical roundoff on input conversion (whether, e.g., (= (string->number? 0.1) 0.1) is defined to be true). 

It's obvious that string->number and read should use the same conversion routine; and I would appreciate a statement in the entry for read that says that the same conversion applies for numbers as in string->number. As for source programs, it might be obvious that any sane compiler will read programs by calling read, but that leaves out the cross-compiler case. Imagine a compiler that outputs assembly language source (or C source) in which floating-point literals are expressed in external form (e.g., PI: .const f'3.1415926'). Then this will be processed by the target assembler (using whatever roundoff, etc it uses), and then used with a runtime that has different characteristics from the cross-compiler, e.g., perhaps the default precision is single rather than double (this isn't crazy, on a game console). 

So I think I'd prefer a statement that says that the relationship between literals in source programs on the one hand and string->number and read on the other is unspecified, but that the latter two use the same conversion rules. If that's already there, please everyone accept my apologies.

-- vincent



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