[Haskell-cafe] There's nothing wrong with infinite types!
stefanor at cox.net
Wed Dec 6 00:14:01 EST 2006
I'm sure anyone who's used Haskell for any significant length of time
has received this error message:
Occurs check: cannot construct the infinite type: t = t -> t1
I for one took that as a challenge, and have implemented a type
inference engine for infinite types.
(a -> b -> c) -> (a -> b) -> a -> c
a -> a
(fix a . (a -> b))
Points of interest:
* There are NO error conditions. it-unifier can assign a type to every
syntactically valid expression of combinatory logic.
* Typechecking is guaranteed to terminate in a linear number of steps,
an (apparently) stronger guarantee than that provided by DHM.
* (Mostly theoretical, since it-unify does not yet support sums or
products): Fixpoint types subsume declared recursive datatypes.
e.g: type List a = fix l . Either () (a,l)
darcs get http://members.cox.net/stefanor/fixtypes/
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