Boolean NoMatch
rascal-0.40.17
Synopsis
Negated [Boolean Match] operator.
Syntax
Pat !:= Exp
Types
//
Pat | Exp | Pat !:= Exp |
|---|---|---|
| [Patterns] | value | bool |
Description
See Patterns for a complete description of the possible patterns on the left-hand side. The expression will return true if the pattern can not match in any way. It will use back-tracking in case the pattern is non-unitary to find a possible match, but it will not backtrack again after it has not found a match unless a larger context mandates it.
Examples
rascal>123 !:= 456;
bool: true
rascal>[10, *n, 50] !:= [10, 20, 30, 40];
bool: true
rascal>{10, *n, 50} !:= {40, 30, 30, 10};
bool: true