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|
use crate::sexp::{SExp, SLeaf, SExp::*, SLeaf::*};
impl SExp {
/**
* Matches this expression against the given pattern,
* that may contain RestPats and variables.
* upon successful match, variable bindings are returned.
*
* Two equal values match:
* ```rust
* use myslip::sexp::{SExp::*, SLeaf::*, util::*};
* assert_eq!(scons(1, Nil).matches_pat(&scons(1, Nil)), Some(vec![]));
* ```
* A variable (wildcard) pattern matches the whole expression:
* ```rust
* use myslip::sexp::{SExp::*, SLeaf::*, util::*};
*
* assert_eq!(
* scons(1, scons(scons(2, scons(3, Nil)), Nil))
* .matches_pat(&var("x")),
* Some(vec![(
* Var("x".to_string()),
* scons(1, scons(scons(2, scons(3, Nil)), Nil))
* )])
* );
* ```
* If a variable has a similar place in structure, it matches
* the corresponding part:
* ```rust
* use myslip::sexp::{SExp::*, SLeaf::*, util::*};
*
* assert_eq!(
* scons(1, scons(scons(2, scons(3, Nil)), Nil))
* .matches_pat(&scons(var("x"), scons(var("y"), Nil))),
* Some(vec![
* (Var("x".to_string()), Atom(Int(1))),
* (Var("y".to_string()), scons(2, scons(3, Nil)))
* ])
* );
* ```
* Rest patterns:
* ```rust
* use myslip::sexp::{SExp::*, SLeaf::*, util::*};
*
* assert_eq!(
* scons(1, scons(2, scons(3, Nil)))
* .matches_pat(&scons(var("x"), scons(RestPat("y".to_string()), Nil))),
* Some(vec![
* (Var("x".to_string()), Atom(Int(1))),
* (RestPat("y".to_string()), scons(2, scons(3, Nil)))
* ])
* );
* ```
*
* Coproducts must be handled individually:
* ```rust
* use myslip::r#type::Type::*;
* use myslip::sexp::{SExp::*, SLeaf::*, util::*};
*
* assert_eq!(
* scons(Coprod, scons(Ty(Boolean), scons(2, Nil)))
* .matches_pat(&scons(Inr, scons(var("x"), Nil))),
* Some(vec![(Var("x".to_string()), Atom(Int(2)))])
* );
* ```
* But they shouldn't match the wrong hand:
* ```rust
* use myslip::r#type::Type::*;
* use myslip::sexp::{SExp::*, SLeaf::*, util::*};
*
* assert_eq!(
* scons(Coprod, scons(Ty(Boolean), scons(2, Nil)))
* .matches_pat(&scons(Inl, scons(var("x"), Nil))),
* None
* );
* ```
*/
pub fn matches_pat(&self, pat: &SExp) -> Option<Vec<(SLeaf, SExp)>> {
match (self, pat) {
(a, b) if a == b => Some(vec![]),
(a, Atom(Var(name))) => Some(vec![(Var(name.to_string()), a.clone())]),
(SCons(cp, ls), SCons(inx, var)) if **cp == Atom(Coprod) => {
let var = match (**var).clone() {
SCons(a, n) if *n == Atom(Nil) => *a,
t => t,
};
let mut ls = (**ls).clone().parts().into_iter();
match (ls.next(), ls.next(), (**inx).clone(), var) {
(Some(l), _, Atom(Inl), Atom(Var(name))) if !l.is_type_atom()
=> Some(vec![(Var(name), l)]),
(_, Some(r), Atom(Inr), Atom(Var(name))) if !r.is_type_atom()
=> Some(vec![(Var(name), r)]),
(Some(l), _, Atom(Inl), pat) if !l.is_type_atom()
=> l.matches_pat(&pat),
(_, Some(r), Atom(Inr), pat) if !r.is_type_atom()
=> r.matches_pat(&pat),
_ => None,
}
},
(SCons(a1, a2), SCons(b1, b2)) => {
let lefthand = a1.matches_pat(b1);
let checkres = (*b2).check_res_pat();
let righthand = match checkres {
Some(name) => Some(vec![(RestPat(name.clone()), *a2.clone())]),
None => a2.matches_pat(b2),
};
lefthand.zip(righthand)
.map(|vs| vs.0.into_iter().chain(vs.1).collect())
},
_ => None,
}
}
fn check_res_pat(&self) -> Option<String> {
match self {
SCons(a, b) => match (*a.clone(), *b.clone()) {
(Atom(RestPat(s)), Atom(Nil)) => Some(s),
_ => None
},
_ => None
}
}
}
|
