Purple.jl

It's interpreters all the way down.
Author JuliaCompilerPlugins
Popularity
9 Stars
Updated Last
1 Year Ago
Started In
May 2021

Purple.jl


This package implements an interesting staging mechanism in Julia -- for a pure subset of Julia functions, it allows lifting of a function defined by signature f : R -> R to a function defined by signature f : Sym{R} -> Term where Sym{R} is a SymbolicUtils.jl value and Term is a SymbolicUtils.jl term.

This package is based on the same fundamental idea as SymbolicTracing.jl but also exposes levels of granularity in tracing by leveraging the optimizer. In addition, insertion of staging conversion functions is computed during type inference and not runtime expansion of @generated functions.

In the future, parts of this package may move over to JuliaSymbolics.

Background

Julia has a wonderfully hackable compiler -- but after type inference, the current pipeline prevents users from exiting and re-entering the pipeline with inferred code. This is for good reason -- unsafe manipulations outside of the context of type inference will invalidate inference and/or otherwise prevent the compiler from ensuring that invariants required by inference hold. Additionally, because the natural place after inference/optimization for code is the runtime cache -- this use case of "leave and go again" is not sufficiently important to warrant careful consideration.

This package is a small attempt to remedy this issue by converting executors (e.g. functions which execute purely and have a natural denotational semantics from some mathematical space to another) into stagers (functions which don't execute normally, but instead create symbolic traces of execution).

Because runtime flows know the types of values which enter into callsites, a stager can create a typed symbolic representation of the runtime flow. This typed symbolic representation can be further compiled by re-emitting Expr instances, or otherwise operated on with the utilities of the JuliaSymbolics ecosystem.

At least, that's the intent -- as with all speculative compiler packages, this one is bound to have some thorns.

For users who are familiar with Mjolnir.jl -- the idea is somewhat similar, except we rely upon Julia's native inference and optimization pipeline (which thus guarantees some modicum of stability).

The Collapse

This package is inspired by Collapsing Towers of Interpreters.