94 lines
1.7 KiB
Rust
94 lines
1.7 KiB
Rust
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/*
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Module: option
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Represents the presence or absence of a value.
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Every option<T> value can either be some(T) or none. Where in other languages
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you might use a nullable type, in Rust you would use an option type.
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*/
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/*
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Tag: t
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The option type
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*/
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tag t<T> {
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/* Variant: none */
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none;
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/* Variant: some */
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some(T);
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}
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/* Section: Operations */
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/*
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Function: get
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Gets the value out of an option
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Failure:
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Fails if the value equals `none`.
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*/
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fn get<copy T>(opt: t<T>) -> T {
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alt opt { some(x) { ret x; } none. { fail "option none"; } }
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}
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/*
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*/
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fn map<T, U>(f: block(T) -> U, opt: t<T>) -> t<U> {
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alt opt { some(x) { some(f(x)) } none. { none } }
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}
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/*
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Function: is_none
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Returns true if the option equals none
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*/
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pure fn is_none<T>(opt: t<T>) -> bool {
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alt opt { none. { true } some(_) { false } }
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}
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/*
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Function: is_some
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Returns true if the option contains some value
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*/
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pure fn is_some<T>(opt: t<T>) -> bool { !is_none(opt) }
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/*
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Function: from_maybe
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Returns the contained value or a default
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*/
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fn from_maybe<T>(def: T, opt: t<T>) -> T {
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alt opt { some(x) { x } none. { def } }
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}
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/*
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Function: maybe
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Applies a function to the contained value or returns a default
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*/
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fn maybe<T, U>(def: U, f: block(T) -> U, opt: t<T>) -> U {
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alt opt { none. { def } some(t) { f(t) } }
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}
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// FIXME: Can be defined in terms of the above when/if we have const bind.
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/*
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Function: may
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Performs an operation on the contained value or does nothing
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*/
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fn may<T>(f: block(T), opt: t<T>) {
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alt opt { none. {/* nothing */ } some(t) { f(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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// End:
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