RetractableFrom SΒΆ

coerce.spad line 75

B is retractable from A means that some elements in A can be converted into elements of B and any element of B can be converted into an element of A.

coerce: % -> S
coerce(a) transforms a into an element of S.
retract: S -> %
retract(a) transforms a into an element of % if possible. Error: if a cannot be made into an element of %.
retractIfCan: S -> Union(%, failed)
retractIfCan(a) transforms a into an element of % if possible. Returns “failed” if a cannot be made into an element of %.