Result of a Mapper. A result of the desired type if
we match. undefined if we don't match.
Return DoNotSetAnyGoals (null) to shortcut evaluation of the present set of rules,
terminating evaluation and guarantee the return of undefined if we've reached this point.
Only do so if you are sure
Type parameters
V
NeverMatch
NeverMatch:null
Functions
isExplicableMapping
isExplicableMapping<F, V>(input: Mapping<F, V>): input is ExplicableMapping<F, V>
Mapping function from F to V