DDIR: slots written as corgi lambdas

[frankmcsherry]

Any term slot may now be a corgi lambda, pat -> body, in corgi's ML syntax. It runs let pat = input in body with input the tuple of the slot's rows: (key, val) for a linear op, (key, left val, right val) for a join. In key, map, and join the body gives (key, val); in value, filter, flatmap, and enter_at it gives the one value.

let edges = input 0 : ((int, int) ; ()) | key(((src, dst), ()) -> ((src), (dst)));
...
    | join(fwd::labels, ((src), (dst), (l)) -> ((dst), (src, l)))
    | filter((_, (_, l, m)) -> (l, m) eq)

Commits

1. Bump corgi to WIP 91df1f0. In corgi's ML, parentheses build a tuple in expressions and patterns as in shapes ((e) a one-field tuple, () the unit), and a tuple pattern takes apart exactly its fields. The effect system is gone (checked ops are words returning a sum; DDIR's out-of-range index already read the zero, so nothing changes there). Builder::graft inlines a graph at a node. Replaces Bump corgi to WIP f20264a: one-field tuples, the unit, checked words, graft #928.
2. Lambda slots.
   • Lexer (parse/pipe.rs): a parenthesized group with a -> outside nested brackets is a lambda, taken as raw text from after the group's last comma before the arrow, so join(other, pat -> body) works. Corgi's syntax (.2, floats, # comments) is never lexed as DDIR.
   • Term::Corgi(src, args) (ir.rs): args are the slot's rows.
   • Corgi backend (corgi/logic.rs): the program is parsed once and grafted into the operator's graph; lower now runs corgi::cse, so a lambda giving both key and val runs once (checked: 16 nodes where two copies would be 25).
   • Row backend: one row at a time, by transcoding. A row whose shape it cannot tell alone (an empty list, a variant) panics there, as transcoding does elsewhere.
   • Explain rewrites a lambda's rows as it does any term's.
   • Parse and shape errors are reported at install, e.g. the pattern (_) takes apart a product of 1 field, not (Int, Int).

Tests

• tests/corgi_lambdas.rs: reach, SCC, and the single-term slots written both ways agree on the vec backend and on corgi at 1 and 3 workers; mismatched patterns, non-integer predicates, and parse errors are refused at install.
• tests/explain.rs: explanations of a lambda program are sufficient, and agree between backends.

cargo test -p interactive --lib --tests and the ddir-server tests pass.

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