Reports single-pattern case expressions, which may be written more concisely or removed entirely.

config =
    [ NoSinglePatternCase.rule
    ]

Fail

Single-pattern case expressions for destructuring are not allowed, as:

type Opaque
    = Opaque Int


unpack : Opaque -> Opaque
unpack o =
    case o of
        Opaque i ->
            i

may instead be written more concisely as:

unpack : Opaque -> Opaque
unpack (Opaque i) =
    i

Similarly, single-pattern case expressions that ase not used for destructuring are not allowed, as:

type AOrB
    = A
    | B


pointless : AOrB -> Bool
pointless aOrB =
    case aOrB of
        _ ->
            True

may instead be written more concisely as:

pointless : AOrB -> Bool
pointless _ =
    True

or

pointless : AOrB -> Bool
pointless =
    always True

Success

Any case expression with more than one pattern match will not be reported. Consider using jfmengels/elm-review-simplify to detect unnecessary multi-pattern cases.

When (not) to enable this rule

This rule is useful if you prefer destructuring in e.g. function arguments or let bindings, rather than in a single-pattern case.

This rule is not useful if you prefer the more verbose style.

Try it out

You can try this rule out by running the following command:

elm-review --template SiriusStarr/elm-review-no-single-pattern-case/example --rules NoSinglePatternCase