very rough draft of informal pattern-guard (qualifiers) explanations

isaac jones ijones at
Sun Jan 7 22:45:04 EST 2007

I just pushed a very rough draft of the plain, informal text for pattern
guards.  I'm also attaching the patch.

I'd like some feedback about the approach I'm taking, which varies
slightly from the description in the 2000 HW paper.

Since "pattern guards" are defined basically as in list comprehensions,
I've pulled a bit of that text into its own section.  In the list
comprehensions section, pattern guards are referred to as "qualifiers",
so I've kept that name.  (From Simon's original memo, it seems that the
generators within the qualifiers are pattern guards.)

So now there's a section that explains qualifiers, including the nested
environment nature.

In many places, I've removed references to guards and replaced them with
references to qualifiers.  I've also consolidated text that explains
guards, which was previously found in various locations, into that
single section as above.

I haven't touched the more semantic bits yet; I'd like some feedback on
my overall approach first.

I've brashly pushed these changes into our darcs repository of the
report in the hopes that others on the committee (or indeed, within the
community) will begin to be a bit more brash.  Alas, I'm unable to
actually build the report at the moment.  If anyone knows how, please
add instructions to the repository, or send them to me and I'll add



p.s. the pattern guard wiki page is here:


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