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(.module:
[library
[lux #*
[abstract
[functor (#+ Functor)]
[apply (#+ Apply)]
["." monad (#+ Monad do)]]
[control
["." try (#+ Try)]]
[data
["." text
["%" format (#+ format)]]
[collection
["." list ("#\." fold)]]]]]
[//
["." exception (#+ Exception exception:)]])
(type: (Cleaner r !)
(-> r (! (Try Any))))
(type: .public (Region r ! a)
{#.doc (example "A region where resources may be be claimed and where a side-effecting computation may be performed."
"Every resource is paired with a function that knows how to clean/reclaim it, to make sure there are no leaks.")}
(-> [r (List (Cleaner r !))]
(! [(List (Cleaner r !))
(Try a)])))
(def: separator
Text
(format text.new_line
"-----------------------------------------" text.new_line
"-----------------------------------------" text.new_line
"-----------------------------------------" text.new_line
text.new_line))
(exception: .public [a] (clean_up_error {error Text}
{output (Try a)})
(format error
(case output
(#try.Success _)
""
(#try.Failure error|output)
(format separator
error|output))))
(def: (clean clean_up output)
(All [a] (-> (Try Any) (Try a) (Try a)))
(case clean_up
(#try.Success _)
output
(#try.Failure error)
(exception.except ..clean_up_error [error output])))
(def: .public (run! monad computation)
{#.doc (example "Executes a region-based computation, with a side-effect determined by the monad.")}
(All [! a]
(-> (Monad !) (All [r] (Region r ! a))
(! (Try a))))
(do {! monad}
[[cleaners output] (computation [[] (list)])]
(|> cleaners
(monad.map ! (function (_ cleaner) (cleaner [])))
(\ ! map (list\fold clean output)))))
(def: .public (acquire! monad cleaner value)
{#.doc (example "Acquire a resource while pairing it a function that knows how to reclaim it.")}
(All [! a] (-> (Monad !) (-> a (! (Try Any))) a
(All [r] (Region r ! a))))
(function (_ [region cleaners])
(\ monad in [(#.Item (function (_ region) (cleaner value))
cleaners)
(#try.Success value)])))
(implementation: .public (functor super)
(All [!]
(-> (Functor !)
(All [r] (Functor (Region r !)))))
(def: (map f)
(function (_ fa)
(function (_ region+cleaners)
(\ super map
(function (_ [cleaners' temp])
[cleaners' (case temp
(#try.Success value)
(#try.Success (f value))
(#try.Failure error)
(#try.Failure error))])
(fa region+cleaners))))))
(implementation: .public (apply super)
(All [!]
(-> (Monad !)
(All [r] (Apply (Region r !)))))
(def: &functor
(..functor (get@ #monad.&functor super)))
(def: (apply ff fa)
(function (_ [region cleaners])
(do super
[[cleaners ef] (ff [region cleaners])
[cleaners ea] (fa [region cleaners])]
(case ef
(#try.Success f)
(case ea
(#try.Success a)
(in [cleaners (#try.Success (f a))])
(#try.Failure error)
(in [cleaners (#try.Failure error)]))
(#try.Failure error)
(in [cleaners (#try.Failure error)]))))))
(implementation: .public (monad super)
(All [!]
(-> (Monad !)
(All [r] (Monad (Region r !)))))
(def: &functor
(..functor (get@ #monad.&functor super)))
(def: (in value)
(function (_ [region cleaners])
(\ super in [cleaners (#try.Success value)])))
(def: (join ffa)
(function (_ [region cleaners])
(do super
[[cleaners efa] (ffa [region cleaners])]
(case efa
(#try.Success fa)
(fa [region cleaners])
(#try.Failure error)
(in [cleaners (#try.Failure error)]))))))
(def: .public (failure monad error)
{#.doc (example "Immediately fail with this 'message'.")}
(All [! a]
(-> (Monad !) Text
(All [r] (Region r ! a))))
(function (_ [region cleaners])
(\ monad in [cleaners (#try.Failure error)])))
(def: .public (except monad exception message)
{#.doc (example "Fail by throwing/raising an exception.")}
(All [! e a]
(-> (Monad !) (Exception e) e
(All [r] (Region r ! a))))
(failure monad (exception.error exception message)))
(def: .public (lifted monad operation)
{#.doc (example "Lift an effectful computation into a region-based computation.")}
(All [! a]
(-> (Monad !) (! a)
(All [r] (Region r ! a))))
(function (_ [region cleaners])
(\ monad map
(|>> #try.Success [cleaners])
operation)))
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