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DEV: Make list slices faster for larger lists.

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This commit is contained in:
Jeremy Wall 2019-11-27 22:17:35 -06:00
parent b8a063fdb8
commit b4c23abbfa
1 changed files with 7 additions and 11 deletions
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18
std/lists.ucg
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@ -82,25 +82,21 @@ let slice = module {
let list_len = list.len(mod.list); let list_len = list.len(mod.list);
let end = select (mod.end is "null", mod.end) => { let end = select (mod.end is "null", mod.end) => {
true = list_len, true = list_len - 1,
}; };
let start = mod.start;
// ensure some invariants // ensure some invariants
(mod.start >= 0) || fail "Slice must be positive"; (start >= 0) || fail "Slice must be positive";
(mod.start <= list_len) || fail "Slice start cannot be larger than the list len of @" % (list_len); (start <= list_len) || fail "Slice start cannot be larger than the list len of @" % (list_len);
(end <= list_len) || fail "Slice end cannot be larger than list len of @" % (list_len); (end <= list_len) || fail "Slice end cannot be larger than list len of @" % (list_len);
let reducer = func(acc, item) => acc{ let reducer = func(acc, item) => acc + [mod.list.(item)];
count = acc.count + 1,
list = select ((acc.count >= mod.start) && (acc.count <= end), acc.list) => {
true = acc.list + [item],
},
};
let result = reduce( let result = reduce(
reducer, reducer,
{count=mod.start, list=[]}, [],
mod.list).list; start:end);
}; };
// zips two lists together. // zips two lists together.