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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.
use std::map;
use std::map::HashMap;
use dvec::DVec;
use cmp::Eq;
use hash::Hash;
use to_bytes::IterBytes;
type hash_interner<T: Const> =
{map: HashMap<T, uint>,
vect: DVec<T>};
fn mk<T:Eq IterBytes Hash Const Copy>() -> interner<T> {
let m = map::HashMap::<T, uint>();
let hi: hash_interner<T> =
{map: m, vect: DVec()};
move (hi as interner::<T>)
}
fn mk_prefill<T:Eq IterBytes Hash Const Copy>(init: ~[T]) -> interner<T> {
let rv = mk();
for init.each() |v| { rv.intern(*v); }
return rv;
}
/* when traits can extend traits, we should extend index<uint,T> to get [] */
trait interner<T:Eq IterBytes Hash Const Copy> {
fn intern(T) -> uint;
fn gensym(T) -> uint;
pure fn get(uint) -> T;
fn len() -> uint;
}
impl <T:Eq IterBytes Hash Const Copy> hash_interner<T>: interner<T> {
fn intern(val: T) -> uint {
match self.map.find(val) {
Some(idx) => return idx,
None => {
let new_idx = self.vect.len();
self.map.insert(val, new_idx);
self.vect.push(val);
return new_idx;
}
}
}
fn gensym(val: T) -> uint {
let new_idx = self.vect.len();
// leave out of .map to avoid colliding
self.vect.push(val);
return new_idx;
}
// this 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(idx: uint) -> T { self.vect.get_elt(idx) }
fn len() -> uint { return self.vect.len(); }
}
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