Created
October 6, 2022 17:25
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Small lambda-calculus parser using nom
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use nom::{ | |
branch::alt, | |
bytes::complete::{tag, take_while}, | |
character::complete::satisfy, | |
combinator::map, | |
IResult, | |
}; | |
#[derive(Debug)] | |
pub enum Term { | |
Var(char), | |
App(Box<Term>, Box<Term>), | |
Abs(char, Box<Term>), | |
} | |
fn whitespaces(input: &str) -> IResult<&str, &str> { | |
take_while(|c: char| c.is_whitespace())(input) | |
} | |
fn var(input: &str) -> IResult<&str, char> { | |
satisfy(|c| char::is_ascii_alphabetic(&c))(input) | |
} | |
fn var_term<'a>(input: &'a str) -> IResult<&'a str, Term> { | |
// println!("{}, var", input); | |
map(var, |c| Term::Var(c))(input) | |
} | |
fn abs<'a>(input: &'a str) -> IResult<&'a str, Term> { | |
// println!("{}, abs", input); | |
let (input, _) = tag(r"\")(input)?; | |
let (input, var_name) = var(input)?; | |
let (input, _) = whitespaces(input)?; | |
let (input, _) = tag(".")(input)?; | |
let (input, _) = whitespaces(input)?; | |
let (input, body) = term(input)?; | |
Ok((input, Term::Abs(var_name, Box::new(body)))) | |
} | |
fn app<'a>(input: &'a str) -> IResult<&'a str, Term> { | |
// println!("{}, app", input); | |
let (input, _) = tag("(")(input)?; | |
let (input, _) = whitespaces(input)?; | |
let (input, fun) = term(input)?; | |
let (input, _) = whitespaces(input)?; | |
let (input, param) = term(input)?; | |
let (input, _) = whitespaces(input)?; | |
let (input, _) = tag(")")(input)?; | |
Ok((input, Term::App(Box::new(fun), Box::new(param)))) | |
} | |
fn term<'a>(input: &'a str) -> IResult<&'a str, Term> { | |
let (input, _) = whitespaces(input)?; | |
alt((var_term, abs, app))(input) | |
} | |
fn main() { | |
println!("{:#?}", abs(r"\x . ( x y )")) | |
} |
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