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use std::fmt::Formatter;
use std::str::FromStr;
use winnow::{
ascii::{alpha1, digit1, multispace0},
combinator::{alt, delimited, opt, preceded, separated, separated_pair},
prelude::*,
Parser,
};
use crate::{Name, Type, TypeScheme};
#[derive(Debug)]
pub struct ParseError(pub(crate) String);
impl std::fmt::Display for ParseError {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
self.0.fmt(f)
}
}
impl std::error::Error for ParseError {}
impl<N: Name> FromStr for TypeScheme<N> {
type Err = ParseError;
/// Parse a [`TypeScheme`] from a string. This round-trips with [`Display`].
/// This is a **leaky** operation and should be avoided wherever possible:
/// names of constructed types will remain until program termination.
///
/// The "for-all" `∀` is optional.
///
/// # Examples
///
/// ```
/// # use polytype::{ptp, tp, TypeScheme};
/// let t_par: TypeScheme = "∀t0. t0 -> t0".parse().expect("invalid type");
/// let t_lit = ptp!(0; @arrow[tp!(0), tp!(0)]);
/// assert_eq!(t_par, t_lit);
///
/// let s = "∀t0. ∀t1. (t1 → t0 → t1) → t1 → list(t0) → t1";
/// let t: TypeScheme<&'static str> = s.parse().expect("invalid type");
/// let round_trip = t.to_string();
/// assert_eq!(s, round_trip);
/// ```
///
/// [`Display`]: https://doc.rust-lang.org/std/fmt/trait.Display.html
/// [`TypeScheme`]: enum.TypeScheme.html
fn from_str(s: &str) -> Result<TypeScheme<N>, ParseError> {
parse_polytype
.parse(s)
.map_err(|e| ParseError(e.to_string()))
}
}
impl<N: Name> FromStr for Type<N> {
type Err = ParseError;
/// Parse a type from a string. This round-trips with [`Display`]. This is a
/// **leaky** operation and should be avoided wherever possible: names of
/// constructed types will remain until program termination.
///
/// # Examples
///
/// ```
/// # use polytype::{tp, Type};
/// let t_par: Type = "int -> hashmap(str, list(bool))".parse().expect("valid type");
/// let t_lit = tp!(@arrow[
/// tp!(int),
/// tp!(hashmap(
/// tp!(str),
/// tp!(list(tp!(bool))),
/// )),
/// ]);
/// assert_eq!(t_par, t_lit);
///
/// let s = "(t1 → t0 → t1) → t1 → list(t0) → t1";
/// let t: Type<&'static str> = s.parse().expect("valid type");
/// let round_trip = t.to_string();
/// assert_eq!(s, round_trip);
/// ```
///
/// [`Display`]: https://doc.rust-lang.org/std/fmt/trait.Display.html
fn from_str(s: &str) -> Result<Type<N>, ParseError> {
parse_monotype
.parse(s)
.map_err(|e| ParseError(e.to_string()))
}
}
fn parse_var<N: Name>(input: &mut &str) -> PResult<Type<N>> {
preceded('t', digit1)
.parse_to()
.map(Type::Variable)
.parse_next(input)
}
fn parse_constructed_simple<N: Name>(input: &mut &str) -> PResult<Type<N>> {
alpha1
.try_map(N::parse)
.map(|name| Type::Constructed(name, vec![]))
.parse_next(input)
}
fn parse_constructed_complex<N: Name>(input: &mut &str) -> PResult<Type<N>> {
let (name, args) = (
alpha1.try_map(N::parse),
delimited(
'(',
separated(
0..,
delimited(multispace0, parse_monotype, multispace0),
',',
),
')',
),
)
.parse_next(input)?;
Ok(Type::Constructed(name, args))
}
fn parse_arrow<N: Name>(input: &mut &str) -> PResult<Type<N>> {
let (alpha, beta) = delimited(
multispace0,
separated_pair(
alt((
parse_parenthetical,
parse_var,
parse_constructed_complex,
parse_constructed_simple,
)),
delimited(multispace0, alt(("→", "->")), multispace0),
parse_monotype,
),
multispace0,
)
.parse_next(input)?;
Ok(Type::arrow(alpha, beta))
}
fn parse_parenthetical<N: Name>(input: &mut &str) -> PResult<Type<N>> {
delimited('(', parse_arrow, ')').parse_next(input)
}
fn parse_binding<N: Name>(input: &mut &str) -> PResult<TypeScheme<N>> {
let (variable, body) = preceded(
opt('∀'),
separated_pair(
preceded('t', digit1).parse_to::<usize>(),
delimited(multispace0, '.', multispace0),
parse_polytype,
),
)
.parse_next(input)?;
let body = Box::new(body);
Ok(TypeScheme::Polytype { variable, body })
}
fn parse_monotype<N: Name>(input: &mut &str) -> PResult<Type<N>> {
alt((
parse_arrow,
parse_var,
parse_constructed_complex,
parse_constructed_simple,
))
.parse_next(input)
}
fn parse_polytype<N: Name>(input: &mut &str) -> PResult<TypeScheme<N>> {
alt((parse_binding, parse_monotype.map(TypeScheme::Monotype))).parse_next(input)
}