Love Pratt parsing! Not a compiler guy, but I've spent way too many hours reflecting on parsing. I remember trying to get though the dragon book so many times and reading all about formal grammar etc. Until I landed on; recursive descent parsing + Pratt for expressions. Super simple technique, and for me is sufficient. I'm sure it doesn't cover all cases, but just for toy languages it feels like we can usually do everything with 2-token lookahead.
Not to step on anyone's toes, I just don't feel that formal grammar theory is that important in practice. :^)
Until you need to do more than all-or-nothing parsing :) see tree-sitter for example, or any other efficient LSP implementation of incremental parsing.
Quick other one: To parse infix expressions, every time you see "x·y | (z | w)", find the operator of least binding power: In my example, I've given "|" less binding power than "·". Anyway, this visually breaks the expression into two halves: "x·y" and "(z | w)". Recursively parse those separately. And repeat.
The symbols "·" and "|" don't mean anything - I've chosen them to be visually intuitive: The "|" is supposed to look like a physical divider. Also, bracketed expressions "(...)" or "{...}" should be parsed first.
Wikipedia mentions that a variant of this got used in FORTRAN I.
I can recommend anyone reading pratts original paper. Its written in a very cool and badass style.
https://dl.acm.org/doi/epdf/10.1145/512927.512931
Love Pratt parsing! Not a compiler guy, but I've spent way too many hours reflecting on parsing. I remember trying to get though the dragon book so many times and reading all about formal grammar etc. Until I landed on; recursive descent parsing + Pratt for expressions. Super simple technique, and for me is sufficient. I'm sure it doesn't cover all cases, but just for toy languages it feels like we can usually do everything with 2-token lookahead.
Not to step on anyone's toes, I just don't feel that formal grammar theory is that important in practice. :^)
It's not for toy languages. Most big compilers use recursive descent parsing.
Until you need to do more than all-or-nothing parsing :) see tree-sitter for example, or any other efficient LSP implementation of incremental parsing.
Quick other one: To parse infix expressions, every time you see "x·y | (z | w)", find the operator of least binding power: In my example, I've given "|" less binding power than "·". Anyway, this visually breaks the expression into two halves: "x·y" and "(z | w)". Recursively parse those separately. And repeat.
The symbols "·" and "|" don't mean anything - I've chosen them to be visually intuitive: The "|" is supposed to look like a physical divider. Also, bracketed expressions "(...)" or "{...}" should be parsed first.
Wikipedia mentions that a variant of this got used in FORTRAN I.
An even simpler way imo, is explicit functions instead of a precedence table, then the code pretty much has the same structure as EBNF.
Need to parse * before +? Begin at add, have it call parse_mul for its left and right sides, and so on.
Then just add more functions as you climb up the precedence levels.You lose in versatility, then you can't add user-defined operators, which is pretty easy with a Pratt parser.