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74 lines
2.2 KiB
Plaintext
74 lines
2.2 KiB
Plaintext
(deftype (Maybe a)
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(Just [a])
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(Nothing []))
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(defmodule Maybe
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(doc apply "applies a function to the value inside `a` if it is a `Just`, and wraps it up again. If it is `Nothing`, it is just returned.")
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(defn apply [a f]
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(match a
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(Nothing) (Nothing)
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(Just x) (Just (~f x))))
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(doc unsafe-from "is an unsafe unwrapper that will get the value from a `Just`. If `a` is `Nothing`, a runtime error will be generated.")
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(defn unsafe-from [a]
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(match a
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(Just x) x))
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(doc from "is an unwrapper that will get the value from a `Just`, or a default value if a `Nothing` is passed.")
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(defn from [a dflt]
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(match a
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(Nothing) dflt
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(Just x) x))
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(doc or-zero "is an unwrapper that will get the value from a `Just`, or build
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a value using `zero` if a `Nothing` is passed.")
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(defn or-zero [a]
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(match a
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(Nothing) (zero)
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(Just x) x))
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(doc just? "checks whether the given value `a` is a `Just`.
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It is the inverse of [`nothing?`](#nothing?).")
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(defn just? [a]
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(match-ref a
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(Nothing) false
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(Just x) true))
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(doc nothing? "checks whether the given value `a` is a `Nothing`.
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It is the inverse of [`just?`](#just?).")
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(defn nothing? [a]
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(match-ref a
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(Nothing) true
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(Just x) false))
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(doc = "equality is defined as the equality of both the constructor and the contained value, i.e. `(Just 1)` and `(Just 1)` are the same, but `(Just 1)` and `(Just 2)` are not.")
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(defn = [a b]
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(match-ref a
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(Nothing) (nothing? b)
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(Just x)
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(match-ref b
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(Nothing) false
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(Just y) (= x y))))
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(implements = Maybe.=)
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(doc unsafe-ptr "Creates a `(Ptr a)` from a `(Maybe a)`. If the `Maybe` was
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`Nothing`, this function will return a `NULL` value.")
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(defn unsafe-ptr [a]
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(match-ref a
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(Nothing) NULL
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(Just _) ((the (Fn [(Ref (Maybe a))] (Ptr a)) Unsafe.coerce) a)))
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(doc from-ptr "Creates a `(Maybe a)` from a `(Ptr a)`. If the `Ptr` was
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`NULL`, this function will return `Nothing`.")
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(defn from-ptr [a]
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(if (null? a)
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(Nothing)
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(Just @(Pointer.to-ref a))))
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(doc zero "returns `Nothing`.")
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(defn zero [] (Nothing))
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(implements zero Maybe.zero)
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)
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