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[spectec] Support ~ and ~_ relation symbols - #2267
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Add support for ~ and ~_ relation symbols (sim and sim_). To avoid a grammar ambiguity between unary logical negation (~ e) and prefix relations without a left-hand side, introduce relop_prefix which excludes ~. In infix position (e1 ~ e2), ~ is parsed as a binary relation (Atom.Sim), while in prefix position (~ e), ~ remains parsed as unary negation (unop).
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@rossberg, this is the new operator you suggested using in WebAssembly/custom-descriptors#101 (comment). I wasn't sure whether you would prefer the spectec PR here upstream first or in the custom-descriptors repo. Landing it here would mean a smaller diff to the custom descriptors repo, so I think that would be slightly nicer. |
rossberg
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Oct 8, 2026
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Mh, yeah, the clash/irregularity with logical negation is a bit unfortunate, but probably okay. Perhaps we should find a more appropriate ASCII spelling for ¬...
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Add support for ~ and ~_ relation symbols (sim and sim_).
To avoid a grammar ambiguity between unary logical negation (~ e)
and prefix relations without a left-hand side, introduce relop_prefix
which excludes
. In infix position (e1 ~ e2), ~ is parsed as a binarye), ~ remains parsedrelation (Atom.Sim), while in prefix position (
as unary negation (unop).