(.module: {#.doc "Composable extensions to the piping macros (|> and <|) that enhance them with various abilities."}
  lux
  (lux (control [monad #+ do]
                ["p" parser])
       (data ["e" error]
             (coll [list #+ "list/" Fold<List> Monad<List>]))
       [macro #+ with-gensyms]
       (macro ["s" syntax #+ syntax: Syntax]
              [code])
       ))

## [Syntax]
(def: body^
  (Syntax (List Code))
  (s.tuple (p.some s.any)))

(syntax: #export (new> [tokens (p.at-least +2 s.any)])
  {#.doc (doc "Ignores the piped argument, and begins a new pipe."
              (|> 20
                  (i/* 3)
                  (i/+ 4)
                  (new> 0 i/inc)))}
  (case (list.reverse tokens)
    (^ (list& _ r-body))
    (wrap (list (` (|> (~+ (list.reverse r-body))))))

    _
    (undefined)))

(syntax: #export (let> binding body prev)
  {#.doc (doc "Gives a name to the piped-argument, within the given expression."
              (|> 5
                  (let> X (i/+ X X))))}
  (wrap (list (` (let [(~ binding) (~ prev)]
                   (~ body))))))

(def: _reverse_
  (Syntax Unit)
  (function [tokens]
    (#e.Success [(list.reverse tokens) []])))

(syntax: #export (cond> [_ _reverse_]
                        prev
                        [else body^]
                        [_ _reverse_]
                        [branches (p.many (p.seq body^ body^))])
  {#.doc (doc "Branching for pipes."
              "Both the tests and the bodies are piped-code, and must be given inside a tuple."
              (|> 5
                  (cond> [i/even?] [(i/* 2)]
                         [i/odd?] [(i/* 3)]
                         [(new> -1)])))}
  (with-gensyms [g!temp]
    (wrap (list (` (with-expansions
                     [(~ g!temp) (~ prev)]
                     (cond (~+ (do list.Monad<List>
                                 [[test then] branches]
                                 (list (` (|> (~ g!temp) (~+ test)))
                                       (` (|> (~ g!temp) (~+ then))))))
                           (|> (~ g!temp) (~+ else)))))))))

(syntax: #export (loop> [test body^] [then body^] prev)
  {#.doc (doc "Loops for pipes."
              "Both the testing and calculating steps are pipes and must be given inside tuples."
              (|> 1
                  (loop> [(i/< 10)]
                         [i/inc])))}
  (with-gensyms [g!temp]
    (wrap (list (` (loop [(~ g!temp) (~ prev)]
                     (if (|> (~ g!temp) (~+ test))
                       ((~' recur) (|> (~ g!temp) (~+ then)))
                       (~ g!temp))))))))

(syntax: #export (do> monad [steps (p.some body^)] prev)
  {#.doc (doc "Monadic pipes."
              "Each steps in the monadic computation is a pipe and must be given inside a tuple."
              (|> 5
                  (do> Monad<Identity>
                       [(i/* 3)]
                       [(i/+ 4)]
                       [i/inc])))}
  (with-gensyms [g!temp]
    (case (list.reverse steps)
      (^ (list& last-step prev-steps))
      (let [step-bindings (do list.Monad<List>
                            [step (list.reverse prev-steps)]
                            (list g!temp (` (|> (~ g!temp) (~+ step)))))]
        (wrap (list (` ((~! do) (~ monad)
                        [(~ g!temp) (~ prev)
                         (~+ step-bindings)]
                        (|> (~ g!temp) (~+ last-step)))))))

      _
      (wrap (list prev)))))

(syntax: #export (exec> [body body^] prev)
  {#.doc (doc "Non-updating pipes."
              "Will generate piped computations, but their results will not be used in the larger scope."
              (|> 5
                  (exec> [int-to-nat %n log!])
                  (i/* 10)))}
  (with-gensyms [g!temp]
    (wrap (list (` (let [(~ g!temp) (~ prev)]
                     (exec (|> (~ g!temp) (~+ body))
                       (~ g!temp))))))))

(syntax: #export (tuple> [paths (p.many body^)] prev)
  {#.doc (doc "Parallel branching for pipes."
              "Allows to run multiple pipelines for a value and gives you a tuple of the outputs."
              (|> 5
                  (tuple> [(i/* 10)]
                          [i/dec (i// 2)]
                          [Int/encode]))
              "Will become: [50 2 \"5\"]")}
  (with-gensyms [g!temp]
    (wrap (list (` (let [(~ g!temp) (~ prev)]
                     [(~+ (list/map (function [body] (` (|> (~ g!temp) (~+ body))))
                                    paths))]))))))

(syntax: #export (case> [branches (p.many (p.seq s.any s.any))] prev)
  {#.doc (doc "Pattern-matching for pipes."
              "The bodies of each branch are NOT pipes; just regular values."
              (|> 5
                  (case> 0 "zero"
                         1 "one"
                         2 "two"
                         3 "three"
                         4 "four"
                         5 "five"
                         6 "six"
                         7 "seven"
                         8 "eight"
                         9 "nine"
                         _ "???")))}
  (wrap (list (` (case (~ prev)
                   (~+ (list/join (list/map (function [[pattern body]] (list pattern body))
                                            branches))))))))