JCjcburnham·Jun 8, 2021
Sure, so I do use petgraph for actually visualizing the lambda DAG graphs, since it's got a very nice graphviz integration: https://github.com/yatima-inc/yatima/blob/059b0abccd0ca54b9a....
You can see the output of that here: https://i.redd.it/94zg24fboyv61.png
(N.B. We removed that module from the language core since we're trying to make that no_std, but we're adding it back to our utils crate soon: https://github.com/yatima-inc/yatima/issues/70)
But we can't use petgraph for the actual computational lambda-DAG because of performance. For example, one thing we get by using pointers is constant-time insertion and removal of of parent nodes (every node in the graph points to their parent). We actually wrote our own Doubly-Linked-List in Rust (it can be done!) to store pointers to the parents for this reason: https://github.com/yatima-inc/y
Read the rest
atima/blob/main/core/src/dll.....
There's also memory concerns, given that the lambda-DAG collects its own garbage, freeing space allocated for nodes when no longer in use, whereas I believe petgraph is just `Vec` internally, which would require shrinking, and that would also be slow.
All this low-level pointer manipulation was, tbh, a huge amount of work, but the end result is a performant lazy lambda-calculus reducer with sharing in a few thousand lines of Rust, which means fast lambdas on wherever WASM runs.
(That said, I'm a little bit concerned about cache misses with all the pointer chasing we do, but I haven't yet gotten around to profiling different Yatima expressions to measure this. Would be a great project for an OSS contributor too, so I'll probably make a GH issue for it!)