View Source Matcha.Context.FilterMap (Matcha v0.1.10)
Functions and operators that :filter_map match specs can use.
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Specs created in this context are unique in that they can differentiate
between specs that fail to find a matching clause for the given input,
and specs with matching clauses that literally return the false value.
They return :no_return in the former case, and {:matched, result} tuples in the latter,
where result can be a literal false returned from a clause.