67 lines
1.6 KiB
Rust
67 lines
1.6 KiB
Rust
import option.some;
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import option.none;
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// FIXME: It would probably be more appealing to define this as
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// type list[T] = rec(T hd, option[@list[T]] tl), but at the moment
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// our recursion rules do not permit that.
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tag list[T] {
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cons(T, @list[T]);
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nil;
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}
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fn foldl[T,U](&list[T] ls, &U u, fn(&T t, &U u) -> U f) -> U {
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alt(ls) {
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case (cons[T](?hd, ?tl)) {
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auto u_ = f(hd, u);
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// FIXME: should use 'be' here, not 'ret'. But parametric
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// tail calls currently don't work.
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ret foldl[T,U](*tl, u_, f);
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}
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case (nil[T]) {
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ret u;
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}
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}
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fail; // TODO: remove me when exhaustiveness checking works
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}
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fn find[T,U](&list[T] ls,
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(fn(&T) -> option.t[U]) f) -> option.t[U] {
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alt(ls) {
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case (cons[T](?hd, ?tl)) {
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alt (f(hd)) {
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case (none[U]) {
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// FIXME: should use 'be' here, not 'ret'. But parametric tail
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// calls currently don't work.
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ret find[T,U](*tl, f);
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}
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case (some[U](?res)) {
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ret some[U](res);
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}
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}
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}
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case (nil[T]) {
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ret none[U];
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}
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}
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fail; // TODO: remove me when exhaustiveness checking works
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}
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fn length[T](&list[T] ls) -> uint {
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fn count[T](&T t, &uint u) -> uint {
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ret u + 1u;
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}
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ret foldl[T,uint](ls, 0u, bind count[T](_, _));
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}
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// Local Variables:
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// mode: rust;
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// fill-column: 78;
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// indent-tabs-mode: nil
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// c-basic-offset: 4
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// buffer-file-coding-system: utf-8-unix
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// compile-command: "make -k -C .. 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
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// End:
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