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// An "interner" is a data structure that associates values with uint tags and
// allows bidirectional lookup; i.e. given a value, one can easily find the
// type, and vice versa.
import std::map;
import std::map::{hashmap, hashfn, eqfn};
import dvec::{dvec, extensions};
type interner<T: const> =
{map: hashmap<T, uint>,
vect: dvec<T>,
hasher: hashfn<T>,
eqer: eqfn<T>};
fn mk<T: const copy>(hasher: hashfn<T>, eqer: eqfn<T>) -> interner<T> {
let m = map::hashmap::<T, uint>(hasher, eqer);
ret {map: m, vect: dvec(), hasher: hasher, eqer: eqer};
}
fn intern<T: const copy>(itr: interner<T>, val: T) -> uint {
alt itr.map.find(val) {
some(idx) { ret idx; }
none {
let new_idx = itr.vect.len();
itr.map.insert(val, new_idx);
itr.vect.push(val);
ret new_idx;
}
}
}
// |get| isn't "pure" in the traditional sense, because it can go from
// failing to returning a value as items are interned. But for typestate,
// where we first check a pred and then rely on it, ceasing to fail is ok.
pure fn get<T: const copy>(itr: interner<T>, idx: uint) -> T {
unchecked {
itr.vect.get_elt(idx)
}
}
fn len<T: const>(itr: interner<T>) -> uint { ret itr.vect.len(); }
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