Prefix form of unary operator in Haskell

Question

In GHCi:

1. Prelude> (+3) 2
   5
2. Prelude> (*3) 2
   6
3. Prelude> (/3) 2
   0.6666666666666666
4. Prelu

Answer 1

As a footnote to grddev's answer, here's the relevant paragraph from the Haskell 98 Report:

The special form -e denotes prefix negation, the only prefix operator in Haskell, and is syntax for negate (e). The binary - operator does not necessarily refer to the definition of - in the Prelude; it may be rebound by the module system. However, unary - will always refer to the negate function defined in the Prelude. There is no link between the local meaning of the - operator and unary negation.

This is something that frustrated me when I first came across it: I couldn't understand why the operators behaved so differently in this context when :info (+) and :info (-) looked basically identical.

You could use subtract, as grddev suggests, or you could just define a new infix operator:

Prelude> let (#) = (-)
Prelude> (# 3) 2
-1

subtract has the advantage of being familiar to other people who might read your code.