Haskell IF statements

Question

I'm pretty new to haskell, but if you make an if statement:

function a b c
     | (a+b == 0) = True
     | --etc.
     | otherwise = False

Is the second if statement the same as an else if in other languages, or is it just another if. I assume its the former as you can only have one output, but I just want to make sure.

Answer 1

The construct you used is called a guard. Haskell checks the given alternatives one after another until one condition yields True. It then evaluates the right hand side of that equation.

You could pretty well write

function n 
   | n == 1 = ...
   | n == 2 = ...
   | n >= 3 = ...

thus the guard kinds of represents an if/elseif construct from other languages. As otherwise is simply defined as True, the last

| otherwise =

will always be true and therefore represents a catch-all else clause.

Nontheless, Haskell has a usual a = if foo then 23 else 42 statement.