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(.module:
[library
[lux #*
[abstract
[apply (#+ Apply)]
[equivalence (#+ Equivalence)]
["." functor (#+ Functor)]
["." monad (#+ Monad do)]]
[meta
["." location]]]])
(type: .public (Try a)
{#.doc (doc "A computation that can fail with an error message.")}
(#Failure Text)
(#Success a))
(implementation: .public functor
(Functor Try)
(def: (map f ma)
(case ma
(#Failure msg)
(#Failure msg)
(#Success datum)
(#Success (f datum)))))
(implementation: .public apply
(Apply Try)
(def: &functor ..functor)
(def: (apply ff fa)
(case ff
(#Success f)
(case fa
(#Success a)
(#Success (f a))
(#Failure msg)
(#Failure msg))
(#Failure msg)
(#Failure msg))))
(implementation: .public monad
(Monad Try)
(def: &functor ..functor)
(def: (in a)
(#Success a))
(def: (join mma)
(case mma
(#Failure msg)
(#Failure msg)
(#Success ma)
ma)))
(implementation: .public (with monad)
{#.doc (doc "Enhances a monad with error-handling functionality.")}
## TODO: Replace (All [a] (! (Try a))) with (functor.Then ! Try)
(All [!] (-> (Monad !) (Monad (All [a] (! (Try a))))))
(def: &functor
(functor.compose (get@ #monad.&functor monad) ..functor))
(def: in
(|>> (\ ..monad in)
(\ monad in)))
(def: (join MeMea)
(do monad
[eMea MeMea]
(case eMea
(#Failure try)
(in (#Failure try))
(#Success Mea)
Mea))))
(def: .public (lifted monad)
{#.doc (doc "Wraps a monadic value with error-handling machinery.")}
(All [! a] (-> (Monad !) (-> (! a) (! (Try a)))))
(\ monad map (\ ..monad in)))
(implementation: .public (equivalence (^open "_\."))
(All [a] (-> (Equivalence a) (Equivalence (Try a))))
(def: (= reference sample)
(case [reference sample]
[(#Success reference) (#Success sample)]
(_\= reference sample)
[(#Failure reference) (#Failure sample)]
("lux text =" reference sample)
_
false
)))
(def: .public (assumed try)
{#.doc (doc "Assumes a Try value succeeded, and yields its value."
"If it didn't, raises the error as a runtime error."
"WARNING: Use with caution.")}
(All [a] (-> (Try a) a))
(case try
(#Success value)
value
(#Failure message)
(error! message)))
(def: .public (maybe try)
(All [a] (-> (Try a) (Maybe a)))
(case try
(#Success value)
(#.Some value)
(#Failure message)
#.None))
(def: .public (of_maybe maybe)
(All [a] (-> (Maybe a) (Try a)))
(case maybe
(#.Some value)
(#Success value)
#.None
(#Failure (`` (("lux in-module" (~~ (static .prelude_module)) .name\encode)
(name_of ..of_maybe))))))
(macro: .public (else tokens compiler)
{#.doc (doc "Allows you to provide a default value that will be used"
"if a (Try x) value turns out to be #Failure."
"Note: the expression for the default value will not be computed if the base computation succeeds."
(= "bar"
(else "foo" (#..Success "bar")))
(= "foo"
(else "foo" (#..Failure "KABOOM!"))))}
(case tokens
(^ (list else try))
(#Success [compiler (list (` (case (~ try)
(#..Success (~' g!temp))
(~' g!temp)
(#..Failure (~ [location.dummy (#.Identifier ["" ""])]))
(~ else))))])
_
(#Failure "Wrong syntax for else")))
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