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