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(;module:
lux
(lux (control functor
applicative
["M" monad #*])))
## [Types]
(type: #export (Result a)
(#Error Text)
(#Success a))
## [Structures]
(struct: #export _ (Functor Result)
(def: (map f ma)
(case ma
(#Error msg) (#Error msg)
(#Success datum) (#Success (f datum)))))
(struct: #export _ (Applicative Result)
(def: functor Functor<Result>)
(def: (wrap a)
(#Success a))
(def: (apply ff fa)
(case ff
(#Success f)
(case fa
(#Success a)
(#Success (f a))
(#Error msg)
(#Error msg))
(#Error msg)
(#Error msg))
))
(struct: #export _ (Monad Result)
(def: applicative Applicative<Result>)
(def: (join mma)
(case mma
(#Error msg) (#Error msg)
(#Success ma) ma)))
(struct: #export (ResultT Monad<M>)
(All [M] (-> (Monad M) (Monad (All [a] (M (Result a))))))
(def: applicative (compA (get@ #M;applicative Monad<M>) Applicative<Result>))
(def: (join MeMea)
(do Monad<M>
[eMea MeMea]
(case eMea
(#Error error)
(wrap (#Error error))
(#Success Mea)
Mea))))
(def: #export (lift Monad<M>)
(All [M a] (-> (Monad M) (-> (M a) (M (Result a)))))
(liftM Monad<M> (:: Monad<Result> wrap)))
(def: #export (succeed value)
(All [a] (-> a (Result a)))
(#Success value))
(def: #export (fail message)
(All [a] (-> Text (Result a)))
(#Error message))
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