On Tue, May 26, 2015 at 8:35 PM, <amindfv@gmail.com> wrote:

Is there any way (without IncoherentInstances or Rebindablesyntax) that I can let the user write e.g. "giveGPA 4.0" (and "giveGPA 4") and get back "F 4" without getting type errors that "4.0"'s type is ambiguous? I can guarantee there won't be any additional instances to "ToGPA"

A typeclass with only one instance is nonsensical, and often a symptom of trying to use typeclasses as OO classes. All it's doing here is hurting you.

In this case, you don't really want to do anything special at all:

giveGPA :: Float -> GPA

giveGPA f = F f

and let Haskell's numeric overloading resolve 4 as (fromInteger 4 :: Float). (Use of the typeclass blocks this.)

--

brandon s allbery kf8nh sine nomine associates

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