Narrowing with strategies in Maude

This is an extension of the Maude strategy language for narrowing (instead of rewriting).

The prototype can be used in two ways, as an extended Maude interpreter or as a command-line tool. For the first option, execute

$ ./snarrow.py [<Maude file>]

and the typical Maude prompt will appear. In addition to the standard Maude commands, it understands snarrow [[<number>]] [in <module name> :] <initial term> using <strategy> ..

Its syntax as a command-line tool is

$ ./snarrow.py <Maude file> [-m <module name>] <initial term> <strategy> [--max-sols <number>]

The output will coincide with that of the equivalent snarrow command.

The command relies on the Python implementation of the strategy language contained in the umaudemc package, which can be installed with pip install umaudemc.

Options

• --no-unify-test does not change matching by unification in the match test (matching is always applied with xmatch and amatch). unify is syntactic sugar for match even if this option is enabled.
• --no-unify-matchrew does not change matching by unification in the matchrew combinator (matching is always applied for xmatchrew and amatchrew). unifynarrow is syntactic sugar for matchrew even if this option is enabled.
• --no-conditional disables narrowing with conditional rules, which is enabled by default. Conditional rules are applied by adding the equational conditions to the narrowing problem of the main pattern, and doing strategy-controlled narrowing search for the rewriting conditions. Rules with rewriting conditions only are never disabled, since the user cannot apply them inadvertently because of their explicit syntax.
• --no-filtered disables variant filtering.

Any (perhaps unconditional) rule in the module can be applied, even those not including the narrowing attribute. The strategy all does a narrowing step using any unconditional rule.

Tests

Several test cases on the Maude files of the test directory can be executed with ./test.sh. The output of this script should coincide with the test.expected file. Namely, there is a Prolog-like logic programming interpreter implementing cut and negation by means of strategies.