Compare syntax paths directly instead of via a generic lexicographic comparator - #840
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Compare syntax paths directly instead of via a generic lexicographic comparator#840jackfirth wants to merge 1 commit into
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…comparator `syntax-path<=>` was built with `(comparator-map (lexicographic-comparator natural<=>) syntax-path-elements)`. That generic implementation drives each comparison through `sequence-generate` on both treelists and crosses a contract boundary for every individual element comparison, which is expensive enough to dominate expansion analysis: `source-analyze` stores every visited syntax object in mutable sorted maps keyed by syntax path, so this comparator runs a logarithmic number of times per observed expansion event. Writing the comparison out as a direct indexed loop over the two treelists cuts analysis time for `xrepl-lib/xrepl/xrepl.rkt` (1877 lines) from ~78 seconds to ~44 seconds. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Docs preview: https://resyntax.notjack.space/preview/840/ |
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Jul 22, 2026
Coverage is 96.591% — perf/syntax-path-comparator into master. No base build found for |
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syntax-path<=>was(comparator-map (lexicographic-comparator natural<=>) syntax-path-elements). That generic implementation drives each comparison throughsequence-generateon both treelists and crosses a contract boundary for every individual element comparison. It's hot enough to dominate expansion analysis, sincesource-analyzekeeps every visited syntax object in sorted maps keyed by syntax path.Writing the comparison out as a direct indexed loop takes analysis of
xrepl-lib/xrepl/xrepl.rkt(1877 lines) from ~71s to ~44s.raco test -p resyntaxpasses.This overlaps with #842 — both attack the cost of
syntax-path<=>, so their speedups don't add. Together they come to ~36s.Found by profiling, in the same vein as #800.
Measurement note: figures are the minimum of 3 runs after a warmup. An earlier version of this description said ~78s → ~44s; that baseline was taken on a thermally throttled machine and overstated the ratio. Repeated runs on identical code vary by up to ~6% here, so treat differences smaller than that as unresolved.