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Does your DSL little language need operator precedence? (utcc.utoronto.ca)

by ingve 10 comments 19 points
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10 comments

[−] bitwize 26d ago
Not if it's s-expression-based! (laughs in smug lisp weenie)
[−] vrighter 25d ago
You can ignore precedence in the grammar, and then use a pratt parser or shunting yard or something to parse the precedence.

But yes, it does need it, usually. And it's not a huge thing to implement. I usually implement it in the grammar, with inline node folding inserted for left associative operators, which gets me a very nice clean AST.

[−] recursivedoubts 26d 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

[−] fjfaase 26d ago
Just a single function per level is sufficient for implementing both right and left association. I do not see the problem.
[−] aappleby 26d 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.