4 ms·

What are these? Do they support rewrite rules on programs?

• BerislavLopac 6y ago
  I meant them in the context of your last paragraph; they are tools that optimize Python for performance. Cython is a compiled superset of Python, while numba is a JIT compiler that works on a subset of Python. I must admit I don't quite understand what rewrite rules actually are; are they akin to macros?
  • thesz 6y ago
    Macros have local scope. They are evaluated to program text only once, probably, lazily. Rewrite rules fire when compiler encounters a chance for them to fire, at any point of (optimizing) program transformation. Due to this fact, rewrite rules are not local - compiler can transform the inner structure of a program changing the locality of program statements. bs = map g xs ... many other lines of program text not reassigning bs as = map f bs still can be transformed into "as = map (f . g) xs" by rule "map f (map g xs) => map (f . g) xs" due to substitution.
    • BerislavLopac 6y ago
      So they -- like macros -- rewrite the source code into something different before the compilation, but -- unlike macros -- only do that under certain circumstances. Would this be a sensible approximation? I'm just trying to understand what they're doing, not why or how. Thank you!