Logical operations on input patterns

[kaya3]

"Input patterns" are used in rewrite rules, observe rules, and some other places to determine matches; conceptually, an input pattern is used as a boolean test on a grid position, where the test is true whereever the pattern matches and false otherwise. It would be interesting to allow logical operations on patterns, e.g. [W..W] and not [.WW.] would match two W symbols with a gap of 2 between them, but only if they are not connected along that gap by W symbols.

This would expand the expressiveness of the language with, potentially, no performance cost: in the current implementation, each DFA state is mapped to an "accept set" which is a set of patterns matched, so any logical operations could be performed at compile-time when computing these "accept sets". (Care would be needed for patterns like not [W], to ensure the DFA's initial 'zero' state still doesn't match them, otherwise the initial call to gridN_update may not correctly report matches in the empty grid. This should be treated like [.] and not [W].)

Additionally, this would eliminate the need for some statements to check whether an output pattern is already present in the grid: a rewrite rule such as a -> b would be equivalent to a and not b -> b. (Currently, this check is only eliminated when it is statically determined that a and b are mutually exclusive.)

[kaya3]

Closed by commit 52d892a07b3a04535384bb290b726523c4c232e7.