Help with precedence

[wstevick]

I'm writing a parser for a functional language, where function application is looks like a b, and a b c is equivalent to (a b) c. I'm having an issue where a - b - c is interpreted as calling a (-(b (-c))) (i.e. calling a with the negative result of calling b with -c). I'd like to solve this using the precedence operators, but haven't been able to find a way.

[ahelwer]

What happens when you make your negative prefix operator have lower precedence than your infix minus operator?

[wstevick]

Doesn't help. Here're my precedences: ```js precedences: () => [ ["apply", "mult", "add", "neg", "trailing_exp"], ], ``` It's still parsing `x - y - z` as `(apply (name) (neg (apply (name) (neg (name)))))))`

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On Wed, Dec 20, 2023 at 12:22 PM Andrew Helwer ***@***.***> wrote: What happens when you make your negative prefix operator have lower precedence than your infix minus operator? — Reply to this email directly, view it on GitHub <#2818 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AZTX2NK3IMYGXVB6GKB7U6LYKMNF3AVCNFSM6AAAAABAOV7X2KVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTQNRUHA2TONJSHE> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[ahelwer]

So your apply operator is higher precedence than infix op expression operator? What about playing around with those?

[wstevick]

I can't figure out a way.

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On Wed, Dec 20, 2023 at 1:45 PM Andrew Helwer ***@***.***> wrote: So your apply operator is higher precedence than infix op expression operator? What about playing around with those? — Reply to this email directly, view it on GitHub <#2818 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AZTX2NPBH2L6DF2NOHLVQRTYKMW43AVCNFSM6AAAAABAOV7X2KVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTQNRUHE3TCNRRHA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[ahelwer]

The way is to make your apply rule lower-precedence than your expression rule. If this isn't resolvable statically you might need to use dynamic precedence with GLR parsing by declaring a conflict.

[wstevick]

What do you mean? Are you saying to have the apply rule lower-precedence than the binary expression rule, or should I create a precedence level for expressions in general?

[ahelwer]

Yes, make your apply rule lower precedence than the binary expression rule and see what happens.

[wstevick]

I have ["neg", "mult", "add", "apply", "trailing_exp"]. The syntax tree is (apply (apply (name) (neg (name))) (neg (name))). Or, (a (-b)) (-c).

Thank you so much for your help.