help from the community?
carette at mcmaster.ca
Thu Feb 1 17:14:27 EST 2007
Malcolm Wallace wrote:
>> If you restrict yourself to programs entirely written by humans, I
>> agree completely. But if you consider programs written by programs
>> (say Template Haskell to be specific, but it could be via many other
>> means), such degenerate types occur rather often.
> I find the "program-generated code" argument rather weak. In that
> past it was used to justify all kinds of minor horrors like excess
> commas in lists and so on. But if one can write a program to generate
> syntactically valid but ugly code, one can easily spend a little extra
> effort on making the result beautiful too.
I used to think so too - but some very hard-won experience  has
changed my mind. Generating good code is very hard. And if you are
doing it in a typeful way (see  again), you may not be able to "spend
a little extra effort" to make the results beautiful, because typeful
code does not let you do introspection very easily.
I will agree with you on one aspect: if the "program-generated code"
done by untyped manipulations, then writing a small type-simplifier is
pretty easy, and my argument is weak. But this is Haskell we're talking
about, and one should really hope that TH will eventually be typed, no?
> After all, which is the more difficult task - devising the auto-coding
> schema, or pretty-printing?
If pretty-printing was all there was to it, I would not have made this
comment. Pretty-printing is indeed easy. Typeful type-level
programming is quite hard.
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