use std::fmt;
use std::str::FromStr;
use crate::*;
use fmt::{Debug, Display, Formatter};
use thiserror::Error;
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Var(Symbol);
#[derive(Debug, Error)]
pub enum VarParseError {
#[error("pattern variable {0:?} should have a leading question mark")]
MissingQuestionMark(String),
}
impl FromStr for Var {
type Err = VarParseError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
use VarParseError::*;
if s.starts_with('?') && s.len() > 1 {
Ok(Var(s.into()))
} else {
Err(MissingQuestionMark(s.to_owned()))
}
}
}
impl Display for Var {
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
Display::fmt(&self.0, f)
}
}
impl Debug for Var {
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
Debug::fmt(&self.0, f)
}
}
#[derive(Default, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Subst {
pub(crate) vec: smallvec::SmallVec<[(Var, Id); 3]>,
}
impl Subst {
pub fn with_capacity(capacity: usize) -> Self {
Self {
vec: smallvec::SmallVec::with_capacity(capacity),
}
}
pub fn insert(&mut self, var: Var, id: Id) -> Option<Id> {
for pair in &mut self.vec {
if pair.0 == var {
return Some(std::mem::replace(&mut pair.1, id));
}
}
self.vec.push((var, id));
None
}
#[inline(never)]
pub fn get(&self, var: Var) -> Option<&Id> {
self.vec
.iter()
.find_map(|(v, id)| if *v == var { Some(id) } else { None })
}
}
impl std::ops::Index<Var> for Subst {
type Output = Id;
fn index(&self, var: Var) -> &Self::Output {
match self.get(var) {
Some(id) => id,
None => panic!("Var '{}={}' not found in {:?}", var.0, var, self),
}
}
}
impl Debug for Subst {
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
let len = self.vec.len();
write!(f, "{{")?;
for i in 0..len {
let (var, id) = &self.vec[i];
write!(f, "{}: {}", var, id)?;
if i < len - 1 {
write!(f, ", ")?;
}
}
write!(f, "}}")
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn var_parse() {
assert_eq!(Var::from_str("?a").unwrap().to_string(), "?a");
assert_eq!(Var::from_str("?abc 123").unwrap().to_string(), "?abc 123");
assert!(Var::from_str("a").is_err());
assert!(Var::from_str("a?").is_err());
assert!(Var::from_str("?").is_err());
}
}