113 lines
1.7 KiB
Rust
113 lines
1.7 KiB
Rust
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/*
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Module: result
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A type representing either success or failure
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*/
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/* Section: Types */
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/*
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Tag: t
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The result type
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*/
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tag t<T, U> {
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/*
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Variant: ok
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Contains the result value
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*/
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ok(T);
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/*
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Variant: err
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Contains the error value
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*/
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err(U);
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}
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/* Section: Operations */
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/*
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Function: get
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Get the value out of a successful result
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Failure:
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If the result is an error
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*/
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fn get<T, U>(res: t<T, U>) -> T {
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alt res {
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ok(t) { t }
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err(_) {
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// FIXME: Serialize the error value
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// and include it in the fail message
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fail "get called on error result";
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}
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}
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}
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/*
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Function: get_err
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Get the value out of an error result
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Failure:
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If the result is not an error
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*/
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fn get_err<T, U>(res: t<T, U>) -> U {
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alt res {
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err(u) { u }
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ok(_) {
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fail "get_error called on ok result";
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}
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}
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}
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/*
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Function: success
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Returns true if the result is <ok>
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*/
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fn success<T, U>(res: t<T, U>) -> bool {
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alt res {
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ok(_) { true }
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err(_) { false }
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}
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}
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/*
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Function: failure
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Returns true if the result is <error>
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*/
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fn failure<T, U>(res: t<T, U>) -> bool {
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!success(res)
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}
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/*
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Function: chain
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Call a function based on a previous result
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If `res` is <ok> then the value is extracted and passed to `op` whereupon
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`op`s result is returned. if `res` is <err> then it is immediately returned.
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This function can be used to compose the results of two functions.
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Example:
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> let res = chain(read_file(file), { |buf|
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> ok(parse_buf(buf))
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> })
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*/
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fn chain<T, copy U, copy V>(res: t<T, V>, op: block(T) -> t<U, V>)
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-> t<U, V> {
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alt res {
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ok(t) { op(t) }
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err(e) { err(e) }
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}
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}
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