90 lines
1.8 KiB
Rust
90 lines
1.8 KiB
Rust
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/*
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Module: either
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A type that represents one of two alternatives
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*/
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/*
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Tag: t
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The either type
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*/
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tag t<T, U> {
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/* Variant: left */
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left(T);
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/* Variant: right */
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right(U);
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}
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/* Section: Operations */
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/*
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Function: either
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Applies a function based on the given either value
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If `value` is left(T) then `f_left` is applied to its contents, if
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`value` is right(U) then `f_right` is applied to its contents, and
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the result is returned.
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*/
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fn either<T, U,
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V>(f_left: block(T) -> V, f_right: block(U) -> V, value: t<T, U>) ->
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V {
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alt value { left(l) { f_left(l) } right(r) { f_right(r) } }
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}
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/*
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Function: lefts
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Extracts from a vector of either all the left values.
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*/
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fn lefts<copy T, U>(eithers: [t<T, U>]) -> [T] {
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let result: [T] = [];
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for elt: t<T, U> in eithers {
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alt elt { left(l) { result += [l]; } _ {/* fallthrough */ } }
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}
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ret result;
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}
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/*
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Function: rights
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Extracts from a vector of either all the right values
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*/
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fn rights<T, copy U>(eithers: [t<T, U>]) -> [U] {
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let result: [U] = [];
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for elt: t<T, U> in eithers {
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alt elt { right(r) { result += [r]; } _ {/* fallthrough */ } }
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}
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ret result;
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}
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/*
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Function: partition
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Extracts from a vector of either all the left values and right values
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Returns a structure containing a vector of left values and a vector of
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right values.
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*/
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fn partition<copy T, copy U>(eithers: [t<T, U>])
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-> {lefts: [T], rights: [U]} {
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let lefts: [T] = [];
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let rights: [U] = [];
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for elt: t<T, U> in eithers {
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alt elt { left(l) { lefts += [l]; } right(r) { rights += [r]; } }
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}
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ret {lefts: lefts, rights: rights};
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}
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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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// End:
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//
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