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121 lines
4.3 KiB
Plaintext
121 lines
4.3 KiB
Plaintext
(deftype (Result a b)
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(Success [a])
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(Error [b]))
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(defmodule Result
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(doc apply "takes a `Result` `a` and applies functions to them, one in the case that it is an `Error`, one in the case that it is a `Success`.")
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(defn apply [a success-f error-f]
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(match a
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(Success x) (Success (~success-f x))
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(Error x) (Error (~error-f x))))
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(doc map "takes a `Result` and applies a function `f` to it if it is a `Success` type, and wraps it back up. In the case that it is an `Error`, it is returned as is.")
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(defn map [a f]
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(match a
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(Success x) (Success (~f x))
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(Error x) (Error x)))
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(doc map-error "takes a `Result` and applies a function `f` to it if it is an `Error` type, and wraps it back up. In the case that it is a `Success`, it is returned as is.")
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(defn map-error [a f]
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(match a
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(Success x) (Success x)
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(Error x) (Error (~f x))))
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(doc and-then "takes a `Result` and applies a function `f` to it if it is a `Success` type. In the case that it is an `Error`, it is returned as is.
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It is thus quite similar to [`map`](#map), but it will unwrap the value.")
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(defn and-then [a f]
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(match a
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(Success x) (~f x)
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(Error x) (Error x)))
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(doc unwrap-or-zero "takes a `Result` and either unwraps it if it is a `Success`, or calls `zero`. `zero` must be defined on the `Success` type.")
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(defn unwrap-or-zero [a]
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(match a
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(Success x) x
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(Error _) (zero)))
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(doc or-else "takes a `Result` and applies a function `f` to it if it is an `Error` type. In the case that it is a `Success`, it is returned as is.
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It is the inverse of [`and-then`](#and-then).")
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(defn or-else [a f]
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(match a
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(Success x) (Success x)
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(Error x) (~f x)))
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(doc unwrap-or-else "takes a `Result` and either unwraps it if it is a `Success`, or calls a function `f` on the value contained in the `Error`.")
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(defn unwrap-or-else [a f]
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(match a
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(Success x) x
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(Error x) (~f x)))
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(doc unsafe-from-success "is an unsafe unwrapper that will get the value from a `Success`. If `a` is an `Error`, a runtime error will be generated.")
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(defn unsafe-from-success [a]
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(match a
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(Success x) x))
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(doc from-success "is an unwrapper that will get the value from a `Success`. If `a` is an `Error`, a default value will be returned.")
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(defn from-success [a dflt]
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(match a
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(Error _) dflt
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(Success x) x))
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(doc unsafe-from-error "is an unsafe unwrapper that will get the value from an `Error`. If `a` is a `Success`, a runtime error will be generated.")
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(defn unsafe-from-error [a]
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(match a
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(Error x) x))
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(doc from-error "is an unwrapper that will get the value from an `Error`. If `a` is a `Success`, a default value will be returned.")
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(defn from-error [a dflt]
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(match a
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(Success _) dflt
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(Error x) x))
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(doc to-maybe "is a function that will convert a `Result` to a `Maybe`, where a `Success` becomes a `Just` and an `Error` becomes a `Nothing`.
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The error value is thrown away.")
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(defn to-maybe [a]
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(match a
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(Success x) (Maybe.Just x)
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(Error _) (Maybe.Nothing)))
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(doc success? "checks whether the given value `a` is a `Success`.
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It is the inverse of [`error?`](#error?).")
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(defn success? [a]
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(match-ref a
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(Error _) false
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(Success _) true))
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(doc error? "checks whether the given value `a` is an `Error`.
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It is the inverse of [`success?`](#success?).")
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(defn error? [a]
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(match-ref a
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(Error _) true
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(Success _) false))
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(doc = "equality is defined as the equality of both the constructor and the contained value, i.e. `(Success 1)` and `(Success 1)` are the same, but `(Success 1)` and `(Success 2)` are not.")
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(defn = [a b]
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(match-ref a
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(Success x)
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(match-ref b
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(Error _) false
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(Success y) (= x y))
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(Error x)
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(match-ref b
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(Success _) false
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(Error y) (= x y))))
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(implements = Result.=)
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)
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(defmodule Maybe
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(doc to-result "is a function that will convert a `Maybe` to a `Result`, where a `Just` becomes a `Success` and a `Nothing` becomes an `Error`.
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You’ll also need to provide an error message `error` that is given to the `Error` constructor if necessary.")
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(defn to-result [a error]
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(match a
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(Nothing) (Result.Error error)
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(Just x) (Result.Success x)))
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)
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