Does flip alter the parameter data types of functions

Question

It seems like flip is doing unexpected things to my functions

Example 1:

let m = flip max
:t max
max :: Ord a => a -> a ->
:t m
m :: () -> () -> ()

Example 2:

let f x y = x + y
:t f
f :: Num a => a -> a -> a
let g = flip f
:t g
g :: Integer -> Integer -> Integer

f can evaluate floating point numbers, but g throws an error when it sees floats. But when I run

(flip f) 1.5 1.7

This evaluates fine! What is the difference between these expressions?

score 12 · Accepted Answer · edited May 23 '17 at 12:25

The dreaded monomorphism restriction strikes again!

This is due to the monomorphism restriction, which causes polymorphic functions to be restricted to a monomorphic type in GHCi. Just run :set -XNoMonomorphismRestriction or give m an explicit type signature to get around this (hint: :set +m enables multiline mode in GHCi).

See these questions for explanations:

Does flip alter the parameter data types of functions

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