/* Module: either A type that represents one of two alternatives */ /* Tag: t The either type */ tag t { /* Variant: left */ left(T); /* Variant: right */ right(U); } /* Section: Operations */ /* Function: either Applies a function based on the given either value If `value` is left(T) then `f_left` is applied to its contents, if `value` is right(U) then `f_right` is applied to its contents, and the result is returned. */ fn either(f_left: block(T) -> V, f_right: block(U) -> V, value: t) -> V { alt value { left(l) { f_left(l) } right(r) { f_right(r) } } } /* Function: lefts Extracts from a vector of either all the left values. */ fn lefts(eithers: [t]) -> [T] { let result: [T] = []; for elt: t in eithers { alt elt { left(l) { result += [l]; } _ {/* fallthrough */ } } } ret result; } /* Function: rights Extracts from a vector of either all the right values */ fn rights(eithers: [t]) -> [U] { let result: [U] = []; for elt: t in eithers { alt elt { right(r) { result += [r]; } _ {/* fallthrough */ } } } ret result; } /* Function: partition Extracts from a vector of either all the left values and right values Returns a structure containing a vector of left values and a vector of right values. */ fn partition(eithers: [t]) -> {lefts: [T], rights: [U]} { let lefts: [T] = []; let rights: [U] = []; for elt: t in eithers { alt elt { left(l) { lefts += [l]; } right(r) { rights += [r]; } } } ret {lefts: lefts, rights: rights}; } /* Function: flip Flips between left and right of a given either */ pure fn flip(eith: t) -> t { alt eith { right(r) { left(r) } left(l) { right(l) } } } /* Function: to_result Converts either::t to a result::t, making the "right" choice an ok result, and the "left" choice a fail */ pure fn to_result(eith: t) -> result::t { alt eith { right(r) { result::ok(r) } left(l) { result::err(l) } } } /* Function: is_left Checks whether the given value is a left */ pure fn is_left(eith: t) -> bool { alt eith { left(_) { true } _ { false } } } /* Function: is_left Checks whether the given value is a right */ pure fn is_right(eith: t) -> bool { alt eith { right(_) { true } _ { false } } } // // Local Variables: // mode: rust // fill-column: 78; // indent-tabs-mode: nil // c-basic-offset: 4 // buffer-file-coding-system: utf-8-unix // End: //