SMIE precedence conflict

Question

(defvar foo-smie-grammar
  (smie-prec2->grammar
   (smie-bnf->prec2
    '((exp (exp "+" exp)
           (exp "*" exp)
           ("let" let-decls "in" exp))
      (let-decls (let-decls ";" let-decls)
                 (exp)))
    '((assoc ";") (assoc "+") (assoc "*")))))

The above gives warnings:

Warning (smie): Conflict: in >/< *
Warning (smie): Conflict: in >/< +
Warning (smie): Total: 2 warnings

Without the let-decls non-terminal, all is fine. How do I fix this? The grammar isn't obviously problematic to me.

Since this is not common knowledge yet: you might like to read this paper that came out recently: https://www.iro.umontreal.ca/~monnier/smie.pdf — Dmitry, May 12 '20 at 20:24

Michael Norrish · Accepted Answer · 2020-05-13T07:09:57.937

1

I need to add an associativity level for in, making it weaker/looser than the other binary operators. E.g., changing the last line to

    '((assoc "in") (assoc ";") (assoc "+") (assoc "*")))))

This is because the parser needs to be able to see that

  let e1 in e2 + e3

should be parsed as

  let e1 in (e2 + e3)

rather than

  (let e1 in e2) + e3

edited May 13 '20 at 07:09

answered May 12 '20 at 03:17

Michael Norrish

185
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SMIE precedence conflict

1 Answers1