Code smell: boolean blindness | Hugonweb Annotated Link Bibliography

This post points out that it's often difficult to tell what a function does when passed true (or false). The given example of the ubiquitous "filter" function is great; does true or false make you keep a list element? Renaming filter to "select" and/or "discard" makes the boolean clearer.

The author points out that substituting a function that returns the Haskell Maybe type makes makes more sense in some "filter" scenarios.

mapMaybe :: (a -> Maybe b) -> [a] -> [b]

builds a list with only entries where the given function returns Just b

See Data.Maybe.mapMaybe for lists and the more general Data.Witherable.mapMaybe.

Related: the wrong abstraction