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use crate::ast::*;
// (λx:T.y): T z
pub fn parse(input: &str) -> Expression {
return parse_str(input).expect("invalid expression");
}
/// Parses a lambda-calculus-like language into an AST.
pub fn parse_str(input: &str) -> Result<Expression, peg::error::ParseError<peg::str::LineCol>> {
// this is kinda awful
// i miss my nim pegs
peg::parser!{
grammar lambda() for str {
rule identifier() -> String
= i:['a'..='z' | 'A'..='Z' | '0'..='9']+ {
i.iter().collect::<String>()
}
rule constant() -> Expression
= p:"-"? c:['0'..='9']+ {
let value = c.iter().collect::<String>().parse::<Value>().unwrap();
Expression::Constant {
term: Term {
val: if let Some(_) = p {
value.wrapping_neg()
} else {
value
},
kind: Type::Empty
}
}
}
rule kind() -> Type
= k:identifier() {
match k.as_str() {
"empty" => Type::Empty,
"unit" => Type::Unit,
"bool" => Type::Bool,
"nat" => Type::Natural,
"int" => Type::Integer,
_ => panic!("invalid type"), // fixme: raise an error
}
}
rule annotation() -> Expression
= e:(conditional() / abstraction() / application() / constant() / variable()) " "* ":" " "* k:kind() {
Expression::Annotation {
expr: Box::new(e),
kind: k
}
}
rule variable() -> Expression
= v:identifier() {
Expression::Variable {
id: v
}
}
rule abstraction() -> Expression
= ("λ" / "lambda ") " "* p:identifier() " "* "." " "* f:expression() {
Expression::Abstraction {
param: p,
func: Box::new(f)
}
}
// fixme: more cases should parse, but how?
rule application() -> Expression
= "(" f:(annotation() / abstraction()) ")" " "* a:expression() {
Expression::Application {
func: Box::new(f),
arg: Box::new(a)
}
}
rule conditional() -> Expression
= "if" " "+ c:expression() " "+ "then" " "+ t:expression() " "+ "else" " "+ e:expression() {
Expression::Conditional {
if_cond: Box::new(c),
if_then: Box::new(t),
if_else: Box::new(e)
}
}
pub rule expression() -> Expression
= e:(conditional() / annotation() / abstraction() / application() / constant() / variable()) {
e
}
pub rule ast() -> Vec<Expression>
= expression() ** ("\n"+)
}
}
// assert_eq!(lambda::expression("(λx:bool.x)").unwrap(), lambda::expression("(λx: bool . x)").unwrap());
return lambda::expression(input.trim());
}
/// Parses a Nim-like language into an AST.
pub fn parse_file(path: &str) -> Vec<Expression> {
todo!();
}
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