Editing Ternary conditional operator (section)

===Haskell===
The built-in if-then-else syntax is inline: the expression

<syntaxhighlight lang="haskell">
if predicate then expr1 else expr2
</syntaxhighlight>

has type

<syntaxhighlight lang="haskell">
Bool -> a -> a -> a
</syntaxhighlight>

The base library also provides the function {{code|Data.Bool.bool}}:

<syntaxhighlight lang="haskell">
bool :: a -> a -> Bool -> a
</syntaxhighlight>

In both cases, no special treatment is needed to ensure that only the selected expression is evaluated, since Haskell is non-strict by default. This also means an operator can be defined that, when used in combination with the {{code|$}} operator, functions exactly like {{code|?:}} in most languages:

<syntaxhighlight lang="haskell">
(?) :: Bool -> a -> a -> a
(?) pred x y = if pred then x else y
infix 1 ?

-- example (vehicle will evaluate to "airplane"):
arg = 'A'
vehicle = arg == 'B' ? "boat" $
          arg == 'A' ? "airplane" $
          arg == 'T' ? "train" $
                       "car"
</syntaxhighlight>

However, it is more idiomatic to use [https://www.haskell.org/onlinereport/haskell2010/haskellch3.html#x8-460003.13 pattern guards]

<syntaxhighlight lang="haskell">
-- example (vehicle will evaluate to "airplane"):
arg = 'A'
vehicle | arg == 'B' = "boat"
        | arg == 'A' = "airplane"
        | arg == 'T' = "train"
        | otherwise  = "car"
</syntaxhighlight>