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MultiVariable Pattern

rascal-0.40.17

Synopsis​

Multi-variable (also known as Splice-variable) in abstract pattern.

Syntax​

* Var

* Type Var

Description​

A multi-variable as nested in a List or Set pattern matches zero or more elements of said container. Optionally the element type of the multi-variable may be specified, in that case only elements that match the specific type are bound to the variable.

Examples​

rascal>import IO;
ok

Using lists:

rascal>if([10, *N, 50] := [10, 20, 30, 40, 50])
>>>>>>>   println("Match succeeds, N == <N>");
Match succeeds, N == [20,30,40]
ok

the above is equivalent with:

rascal>if([10, *int N, 50] := [10, 20, 30, 40, 50])
>>>>>>>   println("Match succeeds, N == <N>");
Match succeeds, N == [20,30,40]
ok

Using sets:

rascal>if({10, *S, 50} := {50, 40, 30, 30, 10})
>>>>>>>   println("Match succeeds, S == <S>");
Match succeeds, S == {40,30}
ok

the above is equivalent with:

rascal>if({10, *int S, 50} := {50, 40, 30, 30, 10})
>>>>>>>   println("Match succeeds, S == <S>");
Match succeeds, S == {40,30}
ok

Pitfalls​

In older versions of Rascal the type of a multi-variable had to be a list or set type.