README.md

Rewriters.jl

This package contains definitions for common combinators that are useful for symbolic expression rewriting. Its purpose is to provide a shared library of combinators between various symbolic programming Julia packages, for example SymbolicUtils.jl, Symbolics.jl and Metatheory.jl.

Documentation

A rewriter is any function which takes an expression and returns an expression or nothing. If nothing is returned that means there was no changes applicable to the input expression.

The Rewriters module contains some types which create and transform rewriters.

• Empty() is a rewriter which always returns nothing
• Chain(itr) chain an iterator of rewriters into a single rewriter which applies each chained rewriter in the given order. If a rewriter returns nothing this is treated as a no-change.
• RestartedChain(itr) like Chain(itr) but restarts from the first rewriter once on the first successful application of one of the chained rewriters.
• IfElse(cond, rw1, rw2) runs the cond function on the input, applies rw1 if cond returns true, rw2 if it retuns false
• If(cond, rw) is the same as IfElse(cond, rw, Empty())
• Prewalk(rw; threaded=false, thread_cutoff=100) returns a rewriter which does a pre-order traversal of a given expression and applies the rewriter rw. Note that if rw returns nothing when a match is not found, then Prewalk(rw) will also return nothing unless a match is found at every level of the walk. threaded=true will use multi threading for traversal. thread_cutoff is the minimum number of nodes in a subtree which should be walked in a threaded spawn.
• Postwalk(rw; threaded=false, thread_cutoff=100) similarly does post-order traversal.
• Fixpoint(rw) returns a rewriter which applies rw repeatedly until there are no changes to be made.
• PassThrough(rw) returns a rewriter which if rw(x) returns nothing will instead return x otherwise will return rw(x).