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feature: unary prefix/suffix operator support via PrattParser (#710)
Closes #461 based on #344 Co-authored-by: Tomas Tauber <me@tomtau.be> Co-authored-by: Klas Segeljakt <klasseg@kth.se>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,16 @@ | ||
| WHITESPACE = _{ " " | "\t" | NEWLINE } | ||
|
|
||
| program = { SOI ~ expr ~ EOI } | ||
| expr = { prefix* ~ primary ~ postfix* ~ (infix ~ prefix* ~ primary ~ postfix* )* } | ||
| infix = _{ add | sub | mul | div | pow } | ||
| add = { "+" } // Addition | ||
| sub = { "-" } // Subtraction | ||
| mul = { "*" } // Multiplication | ||
| div = { "/" } // Division | ||
| pow = { "^" } // Exponentiation | ||
| prefix = _{ neg } | ||
| neg = { "-" } // Negation | ||
| postfix = _{ fac } | ||
| fac = { "!" } // Factorial | ||
| primary = _{ int | "(" ~ expr ~ ")" } | ||
| int = @{ (ASCII_NONZERO_DIGIT ~ ASCII_DIGIT+ | ASCII_DIGIT) } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,109 @@ | ||
| mod parser { | ||
| use pest_derive::Parser; | ||
|
|
||
| #[derive(Parser)] | ||
| #[grammar = "../examples/calc.pest"] | ||
| pub struct Parser; | ||
| } | ||
|
|
||
| use parser::Rule; | ||
| use pest::{ | ||
| iterators::Pairs, | ||
| pratt_parser::{Assoc::*, Op, PrattParser}, | ||
| Parser, | ||
| }; | ||
| use std::io::{stdin, stdout, Write}; | ||
|
|
||
| fn parse_to_str(pairs: Pairs<Rule>, pratt: &PrattParser<Rule>) -> String { | ||
| pratt | ||
| .map_primary(|primary| match primary.as_rule() { | ||
| Rule::int => primary.as_str().to_owned(), | ||
| Rule::expr => parse_to_str(primary.into_inner(), pratt), | ||
| _ => unreachable!(), | ||
| }) | ||
| .map_prefix(|op, rhs| match op.as_rule() { | ||
| Rule::neg => format!("(-{})", rhs), | ||
| _ => unreachable!(), | ||
| }) | ||
| .map_postfix(|lhs, op| match op.as_rule() { | ||
| Rule::fac => format!("({}!)", lhs), | ||
| _ => unreachable!(), | ||
| }) | ||
| .map_infix(|lhs, op, rhs| match op.as_rule() { | ||
| Rule::add => format!("({}+{})", lhs, rhs), | ||
| Rule::sub => format!("({}-{})", lhs, rhs), | ||
| Rule::mul => format!("({}*{})", lhs, rhs), | ||
| Rule::div => format!("({}/{})", lhs, rhs), | ||
| Rule::pow => format!("({}^{})", lhs, rhs), | ||
| _ => unreachable!(), | ||
| }) | ||
| .parse(pairs) | ||
| } | ||
|
|
||
| fn parse_to_i32(pairs: Pairs<Rule>, pratt: &PrattParser<Rule>) -> i128 { | ||
| pratt | ||
| .map_primary(|primary| match primary.as_rule() { | ||
| Rule::int => primary.as_str().parse().unwrap(), | ||
| Rule::expr => parse_to_i32(primary.into_inner(), pratt), | ||
| _ => unreachable!(), | ||
| }) | ||
| .map_prefix(|op, rhs| match op.as_rule() { | ||
| Rule::neg => -rhs, | ||
| _ => unreachable!(), | ||
| }) | ||
| .map_postfix(|lhs, op| match op.as_rule() { | ||
| Rule::fac => (1..lhs + 1).product(), | ||
| _ => unreachable!(), | ||
| }) | ||
| .map_infix(|lhs, op, rhs| match op.as_rule() { | ||
| Rule::add => lhs + rhs, | ||
| Rule::sub => lhs - rhs, | ||
| Rule::mul => lhs * rhs, | ||
| Rule::div => lhs / rhs, | ||
| Rule::pow => (1..rhs + 1).map(|_| lhs).product(), | ||
| _ => unreachable!(), | ||
| }) | ||
| .parse(pairs) | ||
| } | ||
|
|
||
| fn main() { | ||
| let pratt = PrattParser::new() | ||
| .op(Op::infix(Rule::add, Left) | Op::infix(Rule::sub, Left)) | ||
| .op(Op::infix(Rule::mul, Left) | Op::infix(Rule::div, Left)) | ||
| .op(Op::infix(Rule::pow, Right)) | ||
| .op(Op::postfix(Rule::fac)) | ||
| .op(Op::prefix(Rule::neg)); | ||
|
|
||
| let stdin = stdin(); | ||
| let mut stdout = stdout(); | ||
|
|
||
| loop { | ||
| let source = { | ||
| print!("> "); | ||
| let _ = stdout.flush(); | ||
| let mut input = String::new(); | ||
| let _ = stdin.read_line(&mut input); | ||
| input.trim().to_string() | ||
| }; | ||
|
|
||
| let pairs = match parser::Parser::parse(Rule::program, &source) { | ||
| Ok(mut parse_tree) => { | ||
| parse_tree | ||
| .next() | ||
| .unwrap() | ||
| .into_inner() // inner of program | ||
| .next() | ||
| .unwrap() | ||
| .into_inner() // inner of expr | ||
| } | ||
| Err(err) => { | ||
| println!("Failed parsing input: {:}", err); | ||
| continue; | ||
| } | ||
| }; | ||
|
|
||
| print!("{} => ", source); | ||
| print!("{} => ", parse_to_str(pairs.clone(), &pratt)); | ||
| println!("{}", parse_to_i32(pairs.clone(), &pratt)); | ||
| } | ||
| } |
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