#3631: Overload the Prelude iterate to support list input
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Reporter: shelbymoore3 | Owner:
Type: feature request | Status: closed
Priority: normal | Milestone:
Component: Prelude | Version: 6.10.4
Severity: normal | Resolution: wontfix
Keywords: | Difficulty: Unknown
Testcase: | Os: Unknown/Multiple
Architecture: Unknown/Multiple |
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Comment (by shelbymoore3):
Replying to [comment:9 shelbymoore3]:
> Any one who relies on type inference globally can except such domino
cascades generally.
Typo 'except' to 'expects'.
> > Furthermore, your proposed overloading is not parametric in a way
that can easily be captured by type classes. What is the least
generalisation of the the two signatures for iterate?
> >
> > {{{
> > iterate :: (a -> a) -> a -> [a]
> > iterate :: ([a] -> [a]) -> [a] -> [a]
> > }}}
> >
> > Hint: there isn't one.
>
>
> If I am not mistake, a type class can specify the signature that it
expects.
I do assume above that Haskell will not allow a type '[a]' where a type
'a' is expected. If type inference is allowing lists of types to be
assumed where only a type was expected, then IMHO that was a mistake that
opened a very big can of worms. Perhaps I am unaware of some usage that
could not be accomplished otherwise, but it sure seems intuitive to me
that conflation inference in that way would kill scale.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3631#comment:10>
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