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A doElem that starts with an identifier runs every ident-keyed leading parser through the longest-match loop, so each parser there costs work on every such element. One `doErased` parser accepts both the `:=` and the `←` form, which removes one of the two parsers that the `erased` feature added to that loop.
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This PR merges the two
eraseddoElem parsers into one, halving the parse cost the feature added to identifier-headed do elements.A doElem that starts with an identifier runs every ident-keyed leading parser through the longest-match loop.
doErasedanddoErasedArrowboth sat in that set, so every such element paid two failing candidate runs (about 12k instructions together, the bulk of the +0.44% build-instruction report on theerasedPR). One parser accepting both the:=and the←form removes one candidate; on a 2000-element benchmark the added cost drops from +1.80% to +1.04%.The
parseQuotWithCurrentStageoptions inLean.Elab.BuiltinDo.LetandLean.Elab.Do.InferControlInfostay until the next stage0 update carries the merged grammar.