Add null-when-guard-to-match-pattern rule#839
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Fold a `#:when (null? xs)` / `#:when (empty? xs)` guard on a match clause whose pattern ends in a trailing ellipsis variable `xs ...` directly into the pattern by dropping the variable, turning e.g. `[(list 'array elems ...) #:when (null? elems) body]` into `[(list 'array) body]`. Only applies when the trailing variable isn't used in the clause body. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Docs preview: https://resyntax.notjack.space/preview/839/ |
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Coverage is 96.611% — null-when-guard-to-match-pattern into master. No base build found for |
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Adds a rule that folds a
#:when (null? xs)(orempty?) guard into thematchpattern when the clause's pattern ends in a trailing ellipsis variablexs ...that the body doesn't use. So this:becomes:
This came up in an Autofixer PR against Herbie (herbie-fp/herbie#1626, https://github.com/herbie-fp/herbie/blob/25413a2279729497b92c7d35390be595e0a4fd8c/src/syntax/platform-language.rkt#L44-L52).
match-conditional-to-whenhad already lifted a(if (null? elems) #f ...)body into a#:whenguard plus a fallthrough clause, but nothing then noticed the guard could be expressed by the pattern itself. Since Resyntax runs rules to a fixpoint, this new rule composes withmatch-conditional-to-whenso future runs land on the fully simplified form.🤖 Generated with Claude Code