On Feb 6, 2006, at 9:19 AM, Bulat Ziganshin wrote:
Hello Ketil,
Monday, February 06, 2006, 4:06:35 PM, you wrote:
foo :: !Int -> !Int
KM> (Is the second ! actually meaningful?)
yes! it means that the function is strict in its result - i.e.
can't return
undefined value when strict arguments are given. this sort of
knowledge
should help a compiler to "propagate" strictness and figure out the
parts of program that can be compiled as strict code. really, i think
ghc is able to figure functions with strict result just like it is
able to
figure strict function arguments
KM> Personally, I think is much nicer than sprinkling seq's around,
and
KM> generally sufficient. However, there could perhaps be
disambiguities?
btw, it's just implemented in the GHC HEAD
Actually, I think strict _patterns_ are implemented. You are talking
about strict _type annotations_, which is rather different.
As I understand it, strict patterns are just sugar for putting 'seq'
in the right places.
There has been some work dealing with folding strictness and totality
information into types systems; I find the resulting type systems
pretty ugly, and I think they'd be pretty hard to bolt onto an HM base.
Robert Dockins
Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
-- TMBG
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