Lower IList functional combinators to scf loops - #728
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Evaluate right folds as fn(x1, fn(x2, fn(x3, init))), matching the declared callback signature. Update the interpreter and static unroller; Foldl retains accumulator-first calls. This changes Foldr runtime behavior for callbacks sensitive to argument order. Cover subtraction and distinct element and accumulator types in execution, inference, and unrolling.
Add indexed-loop rewrites for Map, Foldl, Foldr, Scan, ForEach, Any, and All, composed by IListToLoop. Preserve callback calls and inferred result types, using singleton concatenation for output lists. Test execution, empty inputs, types, nested control flow, closure captures, callback effects, and repeated application.
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Adds rewrite rules and an
IListToLooppass that lowerMap,Foldl,Foldr,Scan,ForEach,Any, andAllto indexedscf.Forloops.Callbacks remain function calls; Map and Scan build output lists through
singleton concatenation.
The PR contains two commits:
element-first callback signature:
foldr(f, [a, b, c], z) = f(a, f(b, f(c, z))).This changes runtime behavior for callbacks that depend on argument order.
needed and rewrites nested regions within the current method.
Rewriting, e.g., Map to Scf, might induce the existing SCF inference issue for growing loop-carried lists (#512). Rerunning inference after lowering could therefore infer unsound list lengths.