nathsou / girafe

Term Rewriting Systems infrastructure

Girafe

Try it in the playground.

Term Rewriting Systems infrastructure

Girafe provides a set of tools based on a minimal term rewriting systems language that can be interpreted or compiled to various targets.

See the examples/ folder for small demos.

Multiple preprocessors and transformations can be applied to support laziness, imports, currying, non-linearity etc.. see src/Compiler/Passes/

Installing

$ npm install -g girafe

Compiling

Girafe programs can be compiled to javascript, ocaml or haskell using:

$ grf src.grf out.ext js/ocaml/haskell

Or interpreted using:

$ grf src.grf [query]

Use Cases

• Target language for functional (lazy or eager) programming languages (see croco)
• Symbolic computation
• Automated theorem proving
• Abstract data type specifications

Todo

• Use a necessity heuristic when building decision-trees
• Simulate lazy rewriting correctly
• Add targets (c/rust/wasm)
• Confluence checks
• Tail call elimination
• Simple optimizations

References

1. Maranget, Luc (2008) Compiling Pattern Matching to Good Decision Trees
2. Martelli & Montanari (1982) An Efficient Unification Algorithm
3. Fokkink, Wan & Kamperman, Jasper & Walters, Pum. (1999). Lazy Rewriting on Eager Machinery. ACM Transactions on Programming Languages and Systems. 22. 10.1145/345099.345102.
4. Klop, jan willem. (2000). Term Rewriting Systems.

girafe's Issues

Commutative laws can cause infinite loops

I'm trying to express Boolean identities. These ones work:

Or(q, q) -> q
And(q, q) -> q
And(a, Or(b, c)) -> Or(And(a, b), And(a, c))
Or(a, And(b, c)) -> And(Or(a, b), Or(a, c))
Or(a, 1) -> 1
And(a, 0) -> 0
And(a, Or(a, b)) -> a
Or(a, And(a, b)) -> a
And(a, 1) -> a
Or(a, 0) -> a
Not(Not(q)) -> q
Or(a, Not(a)) -> 1
And(a, Not(a)) -> 0
Not(Or(a, b)) -> And(Not(a), Not(b))
Not(And(a, b)) -> Or(Not(a), Not(b))

but when I add the commutative laws,

Or(a, b) -> Or(b, a)
And(a, b) -> And(b, a)

Girafe gets stuck in a loop.

The cummutative laws are needed to simplify the first expression:

> grf binary.grf "And(a, Or(b, a))"     
And_sim2(a, Or_sim1(b, a))
> grf binary.grf "And(a, Or(a, b))"
a

Thanks!