Case analysis for the Bool type. bool x y p evaluates to x when p is False, and evaluates to y when p is True.

This is equivalent to if p then y else x; that is, one can think of it as an if-then-else construct with its arguments reordered.

Examples

>>> bool "foo" "bar" True
"bar"
>>> bool "foo" "bar" False
"foo"

>>> let p = True; x = "bar"; y = "foo"
>>> bool x y p == if p then y else x
True
>>> let p = False
>>> bool x y p == if p then y else x
True

Since: base-4.7.0.0

Boolean operation for monoids.

Returns its first argument when applied to True, returns mempty when applied to False.

Boolean operation for monads, with a monoid default.

Return its first argument when applied to True, returns `return mempty' when applied to False.

Boolean operation for arrows.

Returns its first argument when applied to True, returns returnA when applied to False.

Boolean operation for categories.

Returns its first argument when applied to True, returns Control.Category.id when applied to False.

Boolean operation for monads.

Returns its first argument when applied to True, returns return when applied to False.

Control.Monad.when can be expressed in terms of whenM, like so:

when :: Monad m => Bool -> m () -> m ()
when b m = (const m `whenM` b) ()

Algebra for Bool data type.

The first field of the pair represents the False value, the second field represents the True value.

Catamorphism for booleans.

Anamorphism for booleans.