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use crate::ast::*;
/// Parses a lambda-calculus-like language into an AST.
pub fn parse_lambda(input: &str) -> Result<Expression, peg::error::ParseError<peg::str::LineCol>> {
// this is kinda awful, i miss my simple nim pegs
peg::parser! {
grammar lambda() for str {
rule ident() -> String = i:['a'..='z' | 'A'..='Z' | '0'..='9']+ {
i.iter().collect::<String>()
}
rule bool() -> Expression = b:$("true" / "false") {
match b {
"true" => Expression::Constant { term: Term::Boolean(true) },
"false" => Expression::Constant { term: Term::Boolean(false) },
_ => Expression::Constant { term: Term::Unit() }
}
}
rule num() -> Expression = p:"-"? c:['0'..='9']+ {
let value = c.iter().collect::<String>().parse::<usize>().unwrap();
Expression::Constant {
term: if let Some(_) = p {
Term::Integer(-1 * isize::try_from(value).unwrap())
} else {
Term::Natural(value)
}
}
}
rule cons() -> Expression = c:(bool() / num())
rule primitive() -> Type
= k:$("empty" / "unit" / "bool" / "nat" / "int") {
match k {
"empty" => Type::Empty,
"unit" => Type::Unit,
"bool" => Type::Boolean,
"nat" => Type::Natural,
"int" => Type::Integer,
_ => Type::Empty
}
}
// fixme: brackets are necessary here
rule function() -> Type = "(" f:kind() " "* "->" " "* t:kind() ")" {
Type::Function { from: Box::new(f), to: Box::new(t) }
}
rule kind() -> Type
= k:(function() / primitive()) {
k
}
rule ann() -> Expression
= e:(bracketed() / (cond() / abs() / app() / cons() / var())) " "* ":" " "* k:kind() {
Expression::Annotation {
expr: Box::new(e),
kind: k
}
}
rule var() -> Expression
= v:ident() {
Expression::Variable {
id: v
}
}
rule abs() -> Expression
= ("λ" / "lambda ") " "* p:ident() " "* "." " "* f:expr() {
Expression::Abstraction {
param: p,
func: Box::new(f)
}
}
// fixme: more cases should parse, but how?
rule app() -> Expression
= "(" f:expr() ")" " "* a:expr() {
Expression::Application {
func: Box::new(f),
arg: Box::new(a)
}
}
rule cond() -> Expression
= "if" " "+ c:expr() " "+ "then" " "+ t:expr() " "+ "else" " "+ e:expr() {
Expression::Conditional {
if_cond: Box::new(c),
if_then: Box::new(t),
if_else: Box::new(e)
}
}
rule unbracketed() -> Expression
= e:(cond() / ann() / abs() / app() / cons() / var()) {
e
}
rule bracketed() -> Expression
= "(" " "* e:(cond() / ann() / abs() / app() / cons() / var()) " "* ")" {
e
}
pub rule expr() -> Expression
// what the fuck
// why doesn't = " "* e:(unbracketed() / bracketed()) " "* work
= e:(unbracketed() / bracketed()) {
e
}
}
}
return lambda::expr(input.trim());
}
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