OverlappingPattern Error

Example

not :: Boolean -> Boolean
not true  = false
not _     = true
not false = true

Cause

This error occurs when a pattern matching definition has redundant patterns, i.e., overlapping clauses.

In the example, notice that the third case is redundant (that is, unreachable), as it is covered by the second case (which covers all remaining cases).

Fix

• Remove any redundant cases from the declaration.

Notes