Does your DSL little language need operator precedence?

(utcc.utoronto.ca)

17 points | by ingve 2 days ago

4 comments

  • fjfaase 12 hours ago
    Just a single function per level is sufficient for implementing both right and left association. I do not see the problem.
  • aappleby 14 hours ago
    Yes, but it doesn't need any funny parsing trick to handle them. Just parse the whole statement as a list of expressions joined by operators, and then you can convert the flat list into a precedence-respecting tree with a few lines of code and an operator-to-precedence table.
    • childintime 14 hours ago
      Yes, it's as easy as that. Or check out Jonathan Blow on precedence.

      The infamous dragon book convinced people to use the wrong tools and have the wrong mindset. It was a work of incompetence. There were no dragons, but the book itself.

  • recursivedoubts 18 hours ago
    hyperscript has some operator precedence, but within a given general precedence level you have to explicitly parenthesize if you use different operators:

    https://github.com/bigskysoftware/_hyperscript/blob/06f9078a...

    https://github.com/bigskysoftware/_hyperscript/blob/06f9078a...

    this eliminates most practical precendence questions

    NB: one thing that may strike people as strange is that the parse methods are on the parse elements themselves, I like to localize everything about a parse element in one place

  • bitwize 19 hours ago
    Not if it's s-expression-based! (laughs in smug lisp weenie)
    • aleph_minus_one 18 hours ago
      Or, if the programming language uses infix binary operators:

      Not if the programming language has evaluation order from left to right, e.g.

      2+3*4

      is evaluated as

      (2+3)*4.

      For example J uses this kind of evaluation.

      • Someone 11 hours ago
        J is APL-inspired, and APL is right-associative, so that would surprise me. https://www.jsoftware.com/help/jforc/preliminaries.htm#_Toc1... agrees with that, saying

        “All J verbs (functions and operators) have the same priority and associate right-to-left. For example, a b + c is equivalent to a * (b + c), not (a * b) + c.”*

        Your point about not needing operator precedence still stands, though.

      • lmz 17 hours ago
        Smalltalk also.