janet/src/core/core.janet

# The core janet library
# Copyright 2018 (C) Calvin Rose

###
###
### Macros and Basic Functions
###
###

(var *env*
  "The current environment."
  _env)

(def defn :macro
  "(def name & more)\n\nDefine a function. Equivalent to (def name (fn name [args] ...))."
  (fn defn [name & more]
    (def len (length more))
    (def modifiers @[])
    (var docstr "")
    (def fstart
      (fn recur [i]
        (def {i ith} more)
        (def t (type ith))
        (if (= t :tuple)
          i
          (do
            (if (= t :string)
              (:= docstr ith)
              (array.push modifiers ith))
            (if (< i len) (recur (+ i 1)))))))
    (def start (fstart 0))
    (def args more@start)
    # Add function signature to docstring
    (var index 0)
    (def arglen (length args))
    (def buf (buffer "(" name))
    (while (< index arglen)
      (buffer.push-string buf " ")
      (string.pretty args@index 4 buf)
      (:= index (+ index 1)))
    (array.push modifiers (string buf ")\n\n" docstr))
    # Build return value
    (def fnbody (tuple.prepend (tuple.prepend (tuple.slice more start) name) 'fn))
    (def formargs (array.concat @['def name] modifiers @[fnbody]))
    (tuple.slice formargs 0)))

(defn defmacro :macro
  "Define a macro."
  [name & more]
  (apply defn name :macro more))

(defmacro defmacro-
  "Define a private macro that will not be exported."
  [name & more]
  (apply defn name :macro :private more))

(defmacro defn-
  "Define a private function that will not be exported."
  [name & more]
  (apply defn name :private more))

(defmacro def-
  "Define a private value that will not be exported."
  [name & more]
  (tuple.slice (array.concat @['def name :private] more)))

(defn defglobal
  "Dynamically create a global def."
  [name value]
  (def name* (symbol name))
  (put *env* name* @{:value value})
  nil)

(defn varglobal
  "Dynamically create a global var."
  [name init]
  (def name* (symbol name))
  (put *env* name* @{:ref @[init]})
  nil)

# Basic predicates
(defn even? "Check if x is even." [x] (== 0 (% x 2)))
(defn odd? "Check if x is odd." [x] (not= 0 (% x 2)))
(defn zero? "Check if x is zero." [x] (== x 0))
(defn pos? "Check if x is greater than 0." [x] (> x 0))
(defn neg? "Check if x is less than 0." [x] (< x 0))
(defn one? "Check if x is equal to 1." [x] (== x 1))
(defn integer? "Check if x is an integer." [x] (= (type x) :integer))
(defn real? [x] "Check if x is a real number." (= (type x) :real))
(defn number? "Check if x is a number." [x]
  (def t (type x))
  (if (= t :integer) true (= t :real)))
(defn fiber? "Check if x is a fiber." [x] (= (type x) :fiber))
(defn string? "Check if x is a string." [x] (= (type x) :string))
(defn symbol? "Check if x is a symbol." [x] (= (type x) :symbol))
(defn keyword? "Check if x is a keyword style symbol."
  [x]
  (if (not= (type x) :symbol) nil (= 58 x@0)))
(defn buffer? "Check if x is a buffer." [x] (= (type x) :buffer))
(defn function? "Check if x is a function (not a cfunction)."
  [x] (= (type x) :function))
(defn cfunction? "Check if x a cfunction." [x] (= (type x) :cfunction))
(defn table? [x] "Check if x a table." (= (type x) :table ))
(defn struct? [x] "Check if x a struct." (= (type x) :struct))
(defn array? [x] "Check if x is an array." (= (type x) :array))
(defn tuple? [x] "Check if x is a tuple." (= (type x) :tuple))
(defn boolean? [x] "Check if x is a boolean." (= (type x) :boolean))
(defn bytes? "Check if x is a string, symbol, or buffer." [x]
  (def t (type x))
  (if (= t :string) true (if (= t :symbol) true (= t :buffer))))
(defn dictionary? "Check if x a table or struct." [x]
  (def t (type x))
  (if (= t :table) true (= t :struct)))
(defn indexed? "Check if x is an array or tuple." [x]
  (def t (type x))
  (if (= t :array) true (= t :tuple)))
(defn callable? "Check if x is a function or cfunction." [x]
  (def t (type x))
  (if (= t :function) true (= t :cfunction)))
(defn true? "Check if x is true." [x] (= x true))
(defn false? "Check if x is false." [x] (= x false))
(defn nil? "Check if x is nil." [x] (= x nil))
(defn empty? "Check if xs is empty." [xs] (= 0 (length xs)))
(def atomic?
  "(atomic? x)\n\nCheck if x is a value that evaluates to itself when compiled."
  (do
    (def non-atomic-types
      {:array true
       :tuple true
       :table true
       :buffer true
       :struct true})
    (fn atomic? [x] (not (get non-atomic-types (type x))))))

# C style macros and functions for imperative sugar
(defn inc "Returns x + 1." [x] (+ x 1))
(defn dec "Returns x - 1." [x] (- x 1))
(defmacro ++ "Increments the var x by 1." [x] (tuple ':= x (tuple + x 1)))
(defmacro -- "Decrements the var x by 1." [x] (tuple ':= x (tuple - x 1)))
(defmacro += "Increments the var x by n." [x n] (tuple ':= x (tuple + x n)))
(defmacro -= "Decrements the vat x by n." [x n] (tuple ':= x (tuple - x n)))
(defmacro *= "Shorthand for (:= x (* x n))." [x n] (tuple ':= x (tuple * x n)))
(defmacro /= "Shorthand for (:= x (/ x n))." [x n] (tuple ':= x (tuple / x n)))
(defmacro %= "Shorthand for (:= x (% x n))." [x n] (tuple ':= x (tuple % x n)))
(defmacro &= "Shorthand for (:= x (& x n))." [x n] (tuple ':= x (tuple & x n)))
(defmacro |= "Shorthand for (:= x (| x n))." [x n] (tuple ':= x (tuple | x n)))
(defmacro ^= "Shorthand for (:= x (^ x n))." [x n] (tuple ':= x (tuple ^ x n)))
(defmacro >>= "Shorthand for (:= x (>> x n))." [x n] (tuple ':= x (tuple >> x n)))
(defmacro <<= "Shorthand for (:= x (<< x n))." [x n] (tuple ':= x (tuple << x n)))
(defmacro >>>= "Shorthand for (:= x (>>> x n))." [x n] (tuple ':= x (tuple >>> x n)))

(defmacro default
  "Define a default value for an optional argument.
  Expands to (def sym (if (= nil sym) val sym))"
  [sym val]
  (tuple 'def sym (tuple 'if (tuple = nil sym) val sym)))

(defmacro comment
  "Ignores the body of the comment."
  [])

(defmacro if-not
  "Shorthand for (if (not ... "
  [condition exp-1 exp-2]
  (tuple 'if condition exp-2 exp-1))

(defmacro when
  "Evaluates the body when the condition is true. Otherwise returns nil."
  [condition & body]
  (tuple 'if condition (tuple.prepend body 'do)))

(defmacro unless
  "Shorthand for (when (not ... "
  [condition & body]
  (tuple 'if condition nil (tuple.prepend body 'do)))

(defmacro cond
  "Evaluates conditions sequentially until the first true condition
  is found, and then executes the corresponding body. If there are an
  odd number of forms, the last expression is executed if no forms
  are matched. If there are no matches, return nil."
  [& pairs]
  (defn aux [i]
    (def restlen (- (length pairs) i))
    (if (= restlen 0) nil
      (if (= restlen 1) pairs@i
        (tuple 'if pairs@i
               (get pairs (+ i 1))
               (aux (+ i 2))))))
  (aux 0))

(defmacro case
  "Select the body that equals the dispatch value. When pairs
  has an odd number of arguments, the last is the default expression.
  If no match is found, returns nil"
  [dispatch & pairs]
  (def atm (atomic? dispatch))
  (def sym (if atm dispatch (gensym)))
  (defn aux [i]
    (def restlen (- (length pairs) i))
    (if (= restlen 0) nil
      (if (= restlen 1) pairs@i
        (tuple 'if (tuple = sym pairs@i)
               (get pairs (+ i 1))
               (aux (+ i 2))))))
  (if atm
    (aux 0)
    (tuple 'do
           (tuple 'def sym dispatch)
           (aux 0))))

(defmacro let
  "Create a scope and bind values to symbols. Each pair in bindings is
  assigned as if with def, and the body of the let form returns the last
  value."
  [bindings & body]
  (if (odd? (length bindings)) (error "expected even number of bindings to let"))
  (def len (length bindings))
  (var i 0)
  (var accum @['do])
  (while (< i len)
    (def {i k (+ i 1) v} bindings)
    (array.push accum (tuple 'def k v))
    (+= i 2))
  (array.concat accum body)
  (tuple.slice accum 0))

(defmacro and
  "Evaluates to the last argument if all preceding elements are true, otherwise
  evaluates to false."
  [& forms]
  (def len (length forms))
  (if (= len 0)
    true
    ((fn aux [i]
       (cond
         (>= (+ 1 i) len) forms@i
         (tuple 'if forms@i (aux (+ 1 i)) false))) 0)))

(defmacro or
  "Evaluates to the last argument if all preceding elements are false, otherwise
  evaluates to true."
  [& forms]
  (def len (length forms))
  (if (= len 0)
    false
    ((fn aux [i]
       (def fi forms@i)
       (if
         (>= (+ 1 i) len) fi
         (do
           (if (atomic? fi)
             (tuple 'if fi fi (aux (+ 1 i)))
             (do
               (def $fi (gensym))
               (tuple 'do (tuple 'def $fi fi)
                      (tuple 'if $fi $fi (aux (+ 1 i))))))))) 0)))

(defmacro loop
  "A general purpose loop macro. This macro is similar to the Common Lisp
  loop macro, although intentionally much smaller in scope.
  The head of the loop should be a tuple that contains a sequence of
  either bindings or conditionals. A binding is a sequence of three values
  that define something to loop over. They are formatted like:\n\n
  \tbinding :verb object/expression\n\n
  Where binding is a binding as passed to def, :verb is one of a set of keywords,
  and object is any janet expression. The available verbs are:\n\n
  \t:iterate - repeatedly evaluate and bind to the expression while it is truthy.\n
  \t:range - loop over a range. The object should be two element tuple with a start
  and end value. The range is half open, [start, end).\n
  \t:keys - Iterate over the keys in a data structure.\n
  \t:in - Iterate over the values in an indexed data structure or byte sequence.\n
  \t:generate - Iterate over values yielded from a fiber. Can be paired with the generator
  function for the producer/consumer pattern.\n\n
  loop also accepts conditionals to refine the looping further. Conditionals are of
  the form:\n\n
  \t:modifier argument\n\n
  where :modifier is one of a set of keywords, and argument is keyword dependent.
  :modifier can be one of:\n\n
  \t:while expression - breaks from the loop if expression is falsey.\n
  \t:let bindings - defines bindings inside the loop as passed to the let macro.\n
  \t:before form - evaluates a form for a side effect before of the next inner loop.\n
  \t:after form - same as :before, but the side effect happens after the next inner loop.\n
  \t:repeat n - repeats the next inner loop n times.\n
  \t:when condition - only evaluates the loop body when condition is true.\n\n
  The loop macro always evaluates to nil."
  [head & body]
  (def len (length head))
  (if (not= :tuple (type head))
    (error "expected tuple for loop head"))
  (defn doone
    [i preds &]
    (default preds @['and])
    (if (>= i len)
      (tuple.prepend body 'do)
      (do
        (def {i bindings
              (+ i 1) verb
              (+ i 2) object} head)
        (if (keyword? bindings)
          (case bindings
            :while (do
                     (array.push preds verb)
                     (doone (+ i 2) preds))
            :let (tuple 'let verb (doone (+ i 2) preds))
            :when (tuple 'if verb (doone (+ i 2) preds))
            :before (tuple 'do verb (doone (+ i 2) preds))
            :after (tuple 'do (doone (+ i 2) preds) verb)
            :repeat (do
                      (def $iter (gensym))
                      (def $n (gensym))
                      (def spreds @['and (tuple < $iter $n)])
                      (def sub (doone (+ i 2) spreds))
                      (tuple 'do
                             (tuple 'def $n verb)
                             (tuple 'var $iter 0)
                             (tuple 'while
                                    (tuple.slice spreds)
                                    (tuple := $iter (tuple + 1 $iter))
                                    sub)))
            (error (string "unexpected loop predicate: " bindings)))
          (case verb
            :iterate (do
                       (def $iter (gensym))
                       (def preds @['and (tuple ':= $iter object)])
                       (def subloop (doone (+ i 3) preds))
                       (tuple 'do
                              (tuple 'var $iter nil)
                              (tuple 'while (tuple.slice preds 0)
                                     (tuple 'def bindings $iter)
                                     subloop)))
            :range (do
                     (def [start end _inc] object)
                     (def inc (if _inc _inc 1))
                     (def endsym (gensym))
                     (def $iter (gensym))
                     (def preds @['and (tuple < $iter endsym)])
                     (def subloop (doone (+ i 3) preds))
                     (tuple 'do
                            (tuple 'var $iter start)
                            (tuple 'def endsym end)
                            (tuple 'while (tuple.slice preds 0)
                                   (tuple 'def bindings $iter)
                                   subloop
                                   (tuple ':= $iter (tuple + $iter inc)))))
            :keys (do
                    (def $dict (gensym))
                    (def $iter (gensym))
                    (def preds @['and (tuple not= nil $iter)])
                    (def subloop (doone (+ i 3) preds))
                    (tuple 'do
                           (tuple 'def $dict object)
                           (tuple 'var $iter (tuple next $dict nil))
                           (tuple 'while (tuple.slice preds 0)
                                  (tuple 'def bindings $iter)
                                  subloop
                                  (tuple ':= $iter (tuple next $dict $iter)))))
            :in (do
                  (def $len (gensym))
                  (def $i (gensym))
                  (def $indexed (gensym))
                  (def preds @['and (tuple < $i $len)])
                  (def subloop (doone (+ i 3) preds))
                  (tuple 'do
                         (tuple 'def $indexed object)
                         (tuple 'def $len (tuple length $indexed))
                         (tuple 'var $i 0)
                         (tuple 'while (tuple.slice preds 0)
                                (tuple 'def bindings (tuple get $indexed $i))
                                subloop
                                (tuple ':= $i (tuple + 1 $i)))))
            :generate (do
                     (def $fiber (gensym))
                     (def $yieldval (gensym))
                     (def preds @['and
                                  (do
                                    (def s (gensym))
                                    (tuple 'do
                                           (tuple 'def s (tuple fiber.status $fiber))
                                           (tuple 'or (tuple = s :pending) (tuple = s :new))))])
                     (def subloop (doone (+ i 3) preds))
                     (tuple 'do
                            (tuple 'def $fiber object)
                            (tuple 'var $yieldval (tuple resume $fiber))
                            (tuple 'while (tuple.slice preds 0)
                                   (tuple 'def bindings $yieldval)
                                   subloop
                                   (tuple := $yieldval (tuple resume $fiber)))))
            (error (string "unexpected loop verb: " verb)))))))
  (tuple 'do (doone 0 nil) nil))

(defmacro seq
  "Similar to loop, but accumulates the loop body into an array and returns that.
  See loop for details."
  [head & body]
  (def $accum (gensym))
  (tuple 'do
         (tuple 'def $accum @[])
         (tuple 'loop head
                (tuple array.push $accum
                       (tuple.prepend body 'do)))
         $accum))

(defmacro generate
  "Create a generator expression using the loop syntax. Returns a fiber
  that yields all values inside the loop in order. See loop for details."
  [head & body]
  # `(fiber.new (fn [&] (loop ,head (yield (do ,@body)))))
  (tuple fiber.new
         (tuple 'fn '[&]
                (tuple 'loop head (tuple yield (tuple.prepend body 'do))))))

(defmacro for
  "Do a c style for loop for side effects. Returns nil."
  [binding start end & body]
  (apply loop [tuple binding :range [tuple start end]] body))

(defmacro each
  "Loop over each value in ind. Returns nil."
  [binding ind & body]
  (apply loop [tuple binding :in ind] body))

(defn sum [xs]
  (var accum 0)
  (loop [x :in xs] (+= accum x))
  accum)

(defn product [xs]
  (var accum 1)
  (loop [x :in xs] (*= accum x))
  accum)

(defmacro coro
  "A wrapper for making fibers. Same as (fiber.new (fn [&] ...body))."
  [& body]
  (tuple fiber.new (apply tuple 'fn '[&] body)))

(defmacro if-let
  "Takes the first one or two forms in a vector and if both are true binds
  all the forms with let and evaluates the first expression else
  evaluates the second"
  [bindings tru fal &]
  (def len (length bindings))
  (if (zero? len) (error "expected at least 1 binding"))
  (if (odd? len) (error "expected an even number of bindings"))
  (defn aux [i]
    (def bl bindings@i)
    (def br (get bindings (+ 1 i)))
    (if (>= i len)
      tru
      (do
        (def atm (atomic? bl))
        (def sym (if atm bl (gensym)))
        (if atm
          # Simple binding
          (tuple 'do
                 (tuple 'def sym br)
                 (tuple 'if sym (aux (+ 2 i)) fal))
          # Destructured binding
          (tuple 'do
                 (tuple 'def sym br)
                 (tuple 'if sym
                        (tuple 'do
                               (tuple 'def bl sym)
                               (aux (+ 2 i)))
                        fal))))))
  (aux 0))

(defmacro when-let
  "Takes the first one or two forms in vector and if true binds
  all the forms  with let and evaluates the body"
  [bindings & body]
  (tuple 'if-let bindings (tuple.prepend body 'do)))

(defn comp
  "Takes multiple functions and returns a function that is the composition
  of those functions."
  [& functions]
  (case (length functions)
    0 nil
    1 functions@0
    2 (let [[f g]       functions] (fn [x] (f (g x))))
    3 (let [[f g h]     functions] (fn [x] (f (g (h x)))))
    4 (let [[f g h i]   functions] (fn [x] (f (g (h (i x))))))
    (let [[f g h i j] functions]
      (apply comp (fn [x] (f (g (h (i (j x))))))
             (tuple.slice functions 5 -1)))))

(defn identity
  "A function that returns its first argument."
  [x]
  x)

(defn complement
  "Returns a function that is the complement to the argument."
  [f]
  (fn [x] (not (f x))))

(defn extreme
  "Returns the most extreme value in args based on the function order.
  order should take two values and return true or false (a comparison).
  Returns nil if args is empty."
  [order args]
  (def len (length args))
  (when (pos? len)
    (var ret args@0)
    (loop [i :range [0 len]]
      (def v args@i)
      (if (order v ret) (:= ret v)))
    ret))

(defn max [& args] (extreme > args))
(defn min [& args] (extreme < args))
(defn max-order [& args] (extreme order> args))
(defn min-order [& args] (extreme order< args))

(defn first
  "Get the first element from an indexed data structure."
  [xs]
  xs@0)

(defn last
  "Get the last element from an indexed data structure."
  [xs]
  (get xs (- (length xs) 1)))

###
###
### Indexed Combinators
###
###

(def sort
  "Sort an array in-place. Uses quicksort and is not a stable sort."
  (do

    (defn partition
      [a lo hi by]
      (def pivot a@hi)
      (var i lo)
      (loop [j :range [lo hi]]
        (def aj a@j)
        (when (by aj pivot)
          (def ai a@i)
          (:= a@i aj)
          (:= a@j ai)
          (++ i)))
      (:= a@hi a@i)
      (:= a@i pivot)
      i)

    (defn sort-help
      [a lo hi by]
      (when (> hi lo)
        (def piv (partition a lo hi by))
        (sort-help a lo (- piv 1) by)
        (sort-help a (+ piv 1) hi by))
      a)

    (fn [a by &]
      (sort-help a 0 (- (length a) 1) (or by order<)))))

(defn sorted
  "Returns a new sorted array without modifying the old one."
  [ind by]
  (sort (array.slice ind) by))

(defn reduce
  "Reduce, also know as fold-left in many languages, transforms
  an indexed type (array, tuple) with a function to produce a value."
  [f init ind]
  (var res init)
  (loop [x :in ind]
    (:= res (f res x)))
  res)

(defn map
  "Map a function over every element in an indexed data structure and
  return an array of the results."
  [f & inds]
  (def ninds (length inds))
  (if (= 0 ninds) (error "expected at least 1 indexed collection"))
  (var limit (length inds@0))
  (loop [i :range [0 ninds]]
    (def l (length inds@i))
    (if (< l limit) (:= limit l)))
  (def [i1 i2 i3 i4] inds)
  (def res (array.new limit))
  (case ninds
    1 (loop [i :range [0 limit]] (:= res@i (f i1@i)))
    2 (loop [i :range [0 limit]] (:= res@i (f i1@i i2@i)))
    3 (loop [i :range [0 limit]] (:= res@i (f i1@i i2@i i3@i)))
    4 (loop [i :range [0 limit]] (:= res@i (f i1@i i2@i i3@i i4@i)))
    (loop [i :range [0 limit]]
      (def args (array.new ninds))
      (loop [j :range [0 ninds]] (:= args@j inds@j@i))
      (:= res@i (apply f args))))
  res)

(defn mapcat
  "Map a function over every element in an array or tuple and
  use array to concatenate the results."
  [f ind]
  (def res @[])
  (loop [x :in ind]
    (array.concat res (f x)))
  res)

(defn filter
  "Given a predicate, take only elements from an array or tuple for
  which (pred element) is truthy. Returns a new array."
  [pred ind t &]
  (def res @[])
  (loop [item :in ind]
    (if (pred item)
      (array.push res item)))
  res)

(defn range
  "Create an array of values [start, end) with a given step.
  With one argument returns a range [0, end). With two arguments, returns
  a range [start, end). With three, returns a range with optional step size."
  [& args]
  (case (length args)
    1 (do
        (def [n] args)
        (def arr (array.new n))
        (loop [i :range [0 n]] (put arr i i))
        arr)
    2 (do
        (def [n m] args)
        (def arr (array.new n))
        (loop [i :range [n m]] (put arr (- i n) i))
        arr)
    3 (do
        (def [n m s] args)
        (def arr (array.new n))
        (loop [i :range [n m s]] (put arr (- i n) i))
        arr)
    (error "expected 1 to 3 arguments to range")))

(defn find-index
  "Find the index of indexed type for which pred is true. Returns nil if not found."
  [pred ind]
  (def len (length ind))
  (var i 0)
  (var going true)
  (while (if (< i len) going)
    (def item ind@i)
    (if (pred item) (:= going false) (++ i)))
  (if going nil i))

(defn find
  "Find the first value in an indexed collection that satisfies a predicate. Returns
  nil if not found. Note their is no way to differentiate a nil from the indexed collection
  and a not found. Consider find-index if this is an issue."
  [pred ind]
  (get ind (find-index pred ind)))

(defn take-until
  "Given a predicate, take only elements from an indexed type that satisfy
  the predicate, and abort on first failure. Returns a new array."
  [pred ind]
  (def i (find-index pred ind))
  (if i
    (array.slice ind 0 i)
    ind))

(defn take-while
  "Same as (take-until (complement pred) ind)."
  [pred ind]
  (take-until (complement pred) ind))

(defn drop-until
  "Given a predicate, remove elements from an indexed type that satisfy
  the predicate, and abort on first failure. Returns a new tuple."
  [pred ind]
  (def i (find-index pred ind))
  (array.slice ind i))

(defn drop-while
  "Same as (drop-until (complement pred) ind)."
  [pred ind]
  (drop-until (complement pred) ind))

(defn juxt*
  "Returns the juxtaposition of functions. In other words,
  ((juxt* a b c) x) evaluates to ((a x) (b x) (c x))."
  [& funs]
  (fn [& args]
    (def ret @[])
    (loop [f :in funs]
      (array.push ret (apply f args)))
    (tuple.slice ret 0)))

(defmacro juxt
  "Macro form of juxt*. Same behavior but more efficient."
  [& funs]
  (def parts @['tuple])
  (def $args (gensym))
  (loop [f :in funs]
    (array.push parts (tuple apply f $args)))
  (tuple 'fn (tuple '& $args) (tuple.slice parts 0)))

(defmacro ->
  "Threading macro. Inserts x as the second value in the first form
  in form, and inserts the modified firsts form into the second form
  in the same manner, and so on. Useful for expressing pipelines of data."
  [x & forms]
  (defn fop [last n]
    (def [h t] (if (= :tuple (type n))
                 [tuple n@0 (array.slice n 1)]
                 [tuple n @[]]))
    (def parts (array.concat @[h last] t))
    (tuple.slice parts 0))
  (reduce fop x forms))

(defmacro ->>
  "Threading macro. Inserts x as the last value in the first form
  in form, and inserts the modified firsts form into the second form
  in the same manner, and so on. Useful for expressing pipelines of data."
  [x & forms]
  (defn fop [last n]
    (def [h t] (if (= :tuple (type n))
                 [tuple n@0 (array.slice n 1)]
                 [tuple n @[]]))
    (def parts (array.concat @[h] t @[last]))
    (tuple.slice parts 0))
  (reduce fop x forms))

(defn partial
  "Partial function application."
  [f & more]
  (if (zero? (length more)) f
    (fn [& r] (apply f (array.concat @[] more r)))))

(defn every? 
  "Returns true if the predicate pred is true for every
  value in ind, otherwise false."
  [pred ind]
  (var res true)
  (loop [x :in ind :while res]
    (if (pred x) (:= res false)))
  res)

(defn reverse
  "Reverses the order of the elements in a given array or tuple and returns a new array."
  [t]
  (def len (length t))
  (var n (dec len))
  (def reversed (array.new len))
  (while (>= n 0)
    (array.push reversed t@n)
    (-- n))
  reversed)

(defn invert
  "Returns a table of where the keys of an associative data structure
are the values, and the values of the keys. If multiple keys have the same
value, one key will be ignored."
  [ds]
  (def ret @{})
  (loop [k :keys ds]
    (put ret ds@k k))
  ret)

(defn zipcoll
  "Creates an table or tuple from two arrays/tuples. If a third argument of
  :struct is given result is struct else is table. Returns a new table."
  [keys vals]
  (def res @{})
  (def lk (length keys))
  (def lv (length vals))
  (def len (if (< lk lv) lk lv))
  (loop [i :range [0 len]]
    (put res keys@i vals@i))
  res)

(defn update
  "Accepts a key argument and passes its' associated value to a function.
  The key then, is associated to the function's return value"
  [coll a-key a-function & args]
  (def old-value coll@a-key)
  (:= coll@a-key (apply a-function old-value args)))

(defn merge-into
  "Merges multiple tables/structs into a table. If a key appears in more than one
  collection, then later values replace any previous ones.
  Returns the original table."
  [tab & colls]
  (loop [c :in colls
         key :keys c]
    (:= tab@key c@key))
  tab)

(defn merge
  "Merges multiple tables/structs to one. If a key appears in more than one
  collection, then later values replace any previous ones.
  Returns a new table."
  [& colls]
  (def container @{})
  (loop [c :in colls
         key :keys c]
    (:= container@key c@key))
  container)

(defn keys
  "Get the keys of an associative data structure."
  [x]
  (def arr (array.new (length x)))
  (var k (next x nil))
  (while (not= nil k)
    (array.push arr k)
    (:= k (next x k)))
  arr)

(defn values
  "Get the values of an associative data structure."
  [x]
  (def arr (array.new (length x)))
  (var k (next x nil))
  (while (not= nil k)
    (array.push arr x@k)
    (:= k (next x k)))
  arr)

(defn pairs
  "Get the values of an associative data structure."
  [x]
  (def arr (array.new (length x)))
  (var k (next x nil))
  (while (not= nil k)
    (array.push arr (tuple k x@k))
    (:= k (next x k)))
  arr)

(defn frequencies
  "Get the number of occurrences of each value in a indexed structure."
  [ind]
  (def freqs @{})
  (loop
    [x :in ind]
    (def n freqs@x)
    (:= freqs@x (if n (+ 1 n) 1)))
  freqs)

(defn interleave
  "Returns an array of the first elements of each col,
  then the second, etc."
  [& cols]
  (def res @[])
  (def ncol (length cols))
  (when (> ncol 0)
    (def len (apply min (map length cols)))
    (loop [i :range [0 len]
           ci :range [0 ncol]]
        (array.push res cols@ci@i)))
  res)

###
###
### Documentation
###
###

(var *doc-width*
  "Width in columns to print documentation."
  80)

(defn doc-format
  "Reformat text to wrap at a given line."
  [text]

  (def maxcol (- *doc-width* 8))
  (var buf @"    ")
  (var word @"")
  (var current 0)

  (defn pushword
    []
    (def oldcur current)
    (def spacer
      (if (<= maxcol (+ current (length word) 1))
        (do (:= current 0) "\n    ")
        (do (++ current) " ")))
    (+= current (length word))
    (if (> oldcur 0)
      (buffer.push-string buf spacer))
    (buffer.push-string buf word)
    (buffer.clear word))

  (loop [b :in text]
    (if (and (not= b 10) (not= b 32))
        (if (= b 9)
          (buffer.push-string word "  ")
          (buffer.push-byte word b))
        (do
          (if (> (length word) 0) (pushword))
          (when (= b 10)
            (buffer.push-string buf "\n    ")
            (:= current 0)))))

  # Last word
  (pushword)

  buf)

(defn doc*
  "Get the documentation for a symbol in a given environment."
  [env sym]
  (def x env@sym)
  (if (not x)
    (print "symbol " sym " not found.")
    (do
      (def d x:doc)
      (print "\n\n" (if d (doc-format d) "no documentation found.") "\n\n"))))

(defmacro doc
  "Shows documentation for the given symbol."
  [sym]
  (tuple doc* '_env (tuple 'quote sym)))

###
###
### Macro Expansion
###
###

(defn macroexpand-1
  "Expand macros in a form, but do not recursively expand macros."
  [x]

  (defn dotable [t on-value]
    (def newt @{})
    (var key (next t nil))
    (while (not= nil key)
      (put newt (macroexpand-1 key) (on-value t@key))
      (:= key (next t key)))
    newt)

  (defn expand-bindings [x]
    (case (type x)
      :array (map expand-bindings x)
      :tuple (tuple.slice (map expand-bindings x))
      :table (dotable x expand-bindings)
      :struct (table.to-struct (dotable x expand-bindings))
      (macroexpand-1 x)))

  (defn expanddef [t]
    (def last (get t (- (length t) 1)))
    (def bound t@1)
    (tuple.slice
      (array.concat
        @[t@0 (expand-bindings bound)]
        (tuple.slice t 2 -2)
        @[(macroexpand-1 last)])))

  (defn expandall [t]
    (def args (map macroexpand-1 (tuple.slice t 1)))
    (apply tuple t@0 args))

  (defn expandfn [t]
    (if (symbol? t@1)
      (do
        (def args (map macroexpand-1 (tuple.slice t 3)))
        (apply tuple 'fn t@1 t@2 args))
      (do
        (def args (map macroexpand-1 (tuple.slice t 2)))
        (apply tuple 'fn t@1 args))))

  (def specs
    {':= expanddef
     'def expanddef
     'do expandall
     'fn expandfn
     'if expandall
     'quote identity
     'var expanddef
     'while expandall})

  (defn dotup [t]
    (def h t@0)
    (def s specs@h)
    (def entry (or *env*@h {}))
    (def m entry:value)
    (def m? entry:macro)
    (cond
      s (s t)
      m? (apply m (tuple.slice t 1))
      (tuple.slice (map macroexpand-1 t))))

  (def ret
    (case (type x)
      :tuple (dotup x)
      :array (map macroexpand-1 x)
      :struct (table.to-struct (dotable x macroexpand-1))
      :table (dotable x macroexpand-1)
      x))
  ret)

(defn all? [pred xs]
  (var good true)
  (loop [x :in xs :while good] (if (pred x) nil (:= good false)))
  good)

(defn some? [pred xs]
  (var bad true)
  (loop [x :in xs :while bad] (if (pred x) (:= bad false)))
  (not bad))

(defn deep-not= [x y]
  "Like not=, but mutable types (arrays, tables, buffers) are considered
  equal if they have identical structure. Much slower than not=."
  (def tx (type x))
  (or
    (not= tx (type y))
    (case tx
      :tuple (or (not= (length x) (length y)) (some? identity (map deep-not= x y)))
      :array (or (not= (length x) (length y)) (some? identity (map deep-not= x y)))
      :struct (deep-not= (pairs x) (pairs y))
      :table (deep-not= (table.to-struct x) (table.to-struct y))
      :buffer (not= (string x) (string y))
      (not= x y))))

(defn deep= [x y]
  "Like =, but mutable types (arrays, tables, buffers) are considered
  equal if they have identical structure. Much slower than =."
  (not (deep-not= x y)))

(defn macroexpand
  "Expand macros completely."
  [x]
  (var previous x)
  (var current (macroexpand-1 x))
  (var counter 0)
  (while (deep-not= current previous)
    (if (> (++ counter) 200)
      (error "macro expansion too nested"))
    (:= previous current)
    (:= current (macroexpand-1 current)))
  current)

###
###
### Evaluation and Compilation
###
###

(defn make-env
  [parent &]
  (def parent (if parent parent _env))
  (def newenv (table.setproto @{} parent))
  (put newenv '_env @{:value newenv :private true
                      :doc "The environment table for the current scope."})
  newenv)

(defn run-context
  "Run a context. This evaluates expressions of janet in an environment,
  and is encapsulates the parsing, compilation, and evaluation of janet.
  env is the environment to evaluate the code in, chunks is a function
  that returns strings or buffers of source code (from a repl, file,
  network connection, etc. onvalue and onerr are callbacks that are
  invoked when a result is returned and when an error is produced,
  respectively.

  This function can be used to implement a repl very easily, simply
  pass a function that reads line from stdin to chunks, and print to
  onvalue."
  [env chunks onvalue onerr where &]

  # Are we done yet?
  (var going true)

  # The parser object
  (def p (parser.new))

  # Evaluate 1 source form
  (defn eval1 [source]
    (var good true)
    (def f
      (fiber.new
        (fn []
          (def res (compile source env where))
          (if (= (type res) :function)
            (res)
            (do
              (:= good false)
              (def {:error err :line errl :column errc :fiber errf} res)
              (onerr
                where
                "compile"
                (if (< 0 errl)
                  (string err "\n  in a form at line " errl ", column " errc)
                  err)
                errf))))
        :a))
    (def res (resume f nil))
    (when good
      (def sig (fiber.status f))
      (if going
        (if (= sig :dead)
          (onvalue res)
          (onerr where "runtime" res f)))))

  (def oldenv *env*)
  (:= *env* env)

  # Run loop
  (def buf @"")
  (while going
    (buffer.clear buf)
    (chunks buf p)
    (var pindex 0)
    (def len (length buf))
    (if (= len 0) (:= going false))
    (while (> len pindex)
      (+= pindex (parser.consume p buf pindex))
      (case (parser.status p)
        :full (eval1 (parser.produce p))
        :error (do
                 (def (line col) (parser.where p))
                 (onerr where "parse"
                        (string (parser.error p)
                                " on line " line
                                ", column " col))))))

  (:= *env* oldenv)

  env)

(defn default-error-handler
  [source t x f &]
  (file.write stderr
              (string t " error in " source ": ")
              (if (bytes? x) x (string.pretty x))
              "\n")
  (when f
    (loop
      [nf :in (reverse (fiber.lineage f))
       :before (file.write stderr "  (fiber)\n")
       {:function func
        :tail tail
        :pc pc
        :c c
        :name name
        :source source
        :line source-line
        :column source-col} :in (fiber.stack nf)]
      (file.write stderr "    in")
      (when c (file.write stderr " cfunction"))
      (if name
        (file.write stderr " " name)
        (when func (file.write stderr " <anonymous>")))
      (if source
        (do
          (file.write stderr " [" source "]")
          (if source-line
            (file.write
              stderr
              " on line "
              (string source-line)
              ", column "
              (string source-col)))))
      (if (and (not source-line) pc)
        (file.write stderr " (pc=" (string pc) ")"))
      (when tail (file.write stderr " (tailcall)"))
      (file.write stderr "\n"))))

(defn eval
  "Evaluates a string in the current environment. If more control over the
  environment is needed, use run-context."
  [str]
  (var state (string str))
  (defn chunks [buf _]
    (def ret state)
    (:= state nil)
    (when ret
      (buffer.push-string buf str)
      (buffer.push-string buf "\n")))
  (var returnval nil)
  (run-context *env* chunks (fn [x] (:= returnval x)) default-error-handler "eval")
  returnval)

(do
  (def syspath (or (os.getenv "JANET_PATH") "/usr/local/lib/janet/"))
  (defglobal 'module.paths
    @["./?.janet"
      "./?/init.janet"
      "./janet_modules/?.janet"
      "./janet_modules/?/init.janet"
      (string syspath janet.version "/?.janet")
      (string syspath janet.version "/?/init.janet")
      (string syspath "/?.janet")
      (string syspath "/?/init.janet")])
  (defglobal 'module.native-paths
    @["./?.so"
      "./?/??.so"
      "./janet_modules/?.so"
      "./janet_modules/?/??.so"
      (string syspath janet.version "/?.so")
      (string syspath janet.version "/?/??.so")
      (string syspath "/?.so")
      (string syspath "/?/??.so")]))

(if (= :windows (os.which))
   (loop [i :range [0 (length module.native-paths)]]
     (def x (get module.native-paths i))
     (put
       module.native-paths
       i
       (string.replace ".so" ".dll" x))))

(defn module.find
  [path paths]
  (def parts (string.split "." path))
  (def last (get parts (- (length parts) 1)))
  (def normname (string.replace-all "." "/" path))
  (array.push
    (map (fn [x]
           (def y (string.replace "??" last x))
           (string.replace "?" normname y))
         paths)
    path))

(def require
  "Require a module with the given name. Will search all of the paths in
  module.paths, then the path as a raw file path. Returns the new environment
  returned from compiling and running the file."
  (do

    (defn check-mod
      [f testpath]
      (if f f (file.open testpath)))

    (defn find-mod [path]
      (def paths (module.find path module.paths))
      (reduce check-mod nil paths))

    (defn check-native
      [p testpath]
      (if p
        p
        (do
          (def f (file.open testpath))
          (if f (do (file.close f) testpath)))))

    (defn find-native [path]
      (def paths (module.find path module.native-paths))
      (reduce check-native nil paths))

    (def cache @{})
    (def loading @{})
    (fn require [path args &]
      (when loading@path
        (error (string "circular dependency: module " path " is loading")))
      (def {:exit exit-on-error} (or args {}))
      (def check cache@path)
      (if check
        check
        (do
          (def newenv (make-env))
          (:= cache@path newenv)
          (:= loading@path true)
          (def f (find-mod path))
          (if f
            (do
              # Normal janet module
              (defn chunks [buf _] (file.read f 1024 buf))
              (run-context newenv chunks identity
                           (if exit-on-error
                             (fn [a b c d &] (default-error-handler a b c d) (os.exit 1))
                             default-error-handler)
                           path)
              (file.close f))
            (do
              # Try native module
              (def n (find-native path))
              (if (not n)
                (error (string "could not open file for module " path)))
              ((native n) newenv)))
          (:= loading@path false)
          newenv)))))

(defn import* [env path & args]
  (def targs (apply table args))
  (def {:as as
        :prefix prefix} targs)
  (def newenv (require path targs))
  (var k (next newenv nil))
  (def {:meta meta} newenv)
  (def prefix (or (and as (string as ".")) prefix (string path ".")))
  (while k
    (def v newenv@k)
    (when (not v:private)
      (def newv (table.setproto @{:private true} v))
      (put env (symbol prefix k) newv))
    (:= k (next newenv k))))

(defmacro import
  "Import a module. First requires the module, and then merges its
  symbols into the current environment, prepending a given prefix as needed.
  (use the :as or :prefix option to set a prefix). If no prefix is provided,
  use the name of the module as a prefix."
  [path & args]
  (def argm (map (fn [x]
                   (if (keyword? x)
                     x
                     (string x)))
                 args))
  (apply tuple import* '_env (string path) argm))

(defn repl
  "Run a repl. The first parameter is an optional function to call to
  get a chunk of source code. Should return nil for end of file."
  [chunks onvalue onerr &]
  (def newenv (make-env))
  (default chunks (fn [&] (file.read stdin :line)))
  (default onvalue (fn [x]
                     (put newenv '_ @{:value x})
                     (print (string.pretty x 20))))
  (default onerr default-error-handler)
  (run-context newenv chunks onvalue onerr "repl"))

(defn all-symbols
  "Get all symbols available in the current environment."
  [env &]
  (default env *env*)
  (def envs @[])
  (do (var e env) (while e (array.push envs e) (:= e (table.getproto e))))
  (def symbol-set @{})
  (loop [envi :in envs
         k :keys envi]
    (:= symbol-set@k true))
  (sort (keys symbol-set)))

(defmacro qq
  "Quasiquote."
  [x]
  (defn- uqs? [x]
    (and (tuple? x) (= x@0 'uqs)))
  (defn- uqs [x]
    (if (uqs? x)
      (tuple apply array x@1)
      @[(qq x)]))
  (case (type x)
    :symbol (tuple 'quote x)
    :tuple (cond 
             (= x@0 'uq) x@1
             (some? uqs? x) (tuple  tuple.slice (tuple.prepend (map uqs x) array.concat))
             (apply tuple tuple (map qq x)))
    :array (apply array (map qq x))
    :struct (apply struct (interleave (map qq (keys x)) (map qq (values x))))
    :table (apply table (interleave (map qq (keys x)) (map qq (values x))))
    x))