Type Inferences of Ambiguous Literals

The Haskell code below works.

main = print $ x + y
x = 1
y = 2.3

This results 3.3. x isn't Int because x is used with (+) operator that also takes 2.3.

On the other hand, the code below causes a type error in compile time.

main = print $ x + y
x = 1
y = 2.3

z = x :: Int

error:

No instance for (Fractional Int)
  arising from the literal `2.3'
Possible fix: add an instance declaration for (Fractional Int)
In the expression: 2.3
In an equation for `y': y = 2.3

You can make x ambiguous with NoMonomorphismRestriction option.

{-# LANGUAGE NoMonomorphismRestriction #-}

or -XNoMonomorphismRestriction in command line option.

• http://stackoverflow.com/questions/7055146/why-do-3-and-x-which-was-assigned-3-have-different-inferred-types-in-haskell

Thanks @ikegami__!