Community documentation for Janet

(count even? [1 2 3 4 5])  # => 2

(count  (fn [x] (> x 3))  [1 2 3 4 5])  # => 2
(count         |(> $ 3)   [1 2 3 4 5])  # => 2

(count  (fn [x] (truthy? x))  [nil false true 42 :a "foo"])  # => 4
(count         |(truthy? $)   [nil false true 42 :a "foo"])  # => 4

(var f even?)
(count f [1 2 3 4 5])  # => 2
(set f odd?)
(count f [1 2 3 4 5])  # => 3

(map  (fn [f] (count f [1 2 3 4 5]))  [even? odd?])  # => @[2 3]
(map         |(count $ [1 2 3 4 5])   [even? odd?])  # => @[2 3]

(buffer/bit-set @"hahaha" 3) # => @"hahaha"

(buffer/bit-set @"what" 3) # => @"\x7Fhat"

(def f (generate [i :range [0 5]] (+ i i)))

(print (fiber/status f))
(print (resume f)) 
(print (resume f)) 
(print (resume f)) 
(print (resume f)) 
(print (resume f)) 
(print (fiber/status f)) # -> :pending
(print (resume f)) 
(print (fiber/status f)) # -> :dead


# :new
# 0
# 2
# 4
# 6
# 8
# :pending
#
# :dead

(in "yo" 0)
# => 121

(mean [1 10 100])  # => 37
(mean [])          # => nan

(pp (all-bindings))
# => prints @[% %= * ... yield zero? zipcoll]

(def a "A")
(pp (all-bindings (curenv) true))
# => prints @[_ a] - only local bindings are listed

# due to 0 indexing, you will often want to add 1 to things:
(defn short-date [d]
  (let [{:year y :month mon :month-day d} d]
    (string y "-" (+ 1 mon) "-" (+ 1 d))))

# Makes os/date like 2025-12-25
(short-date (os//date))


# From: https://codeberg.org/veqq/deforester/src/branch/master/deforester.janet
(defn- time-string 
  ``Gives current time as ISO 8601 string: 2025-10-12T11:43:14 https://en.wikipedia.org/wiki/ISO_8601
  This accounts for `os/date` 0-indexing month and days which are 1-indexed in ISO 8601.``
  []
  (let [{:year y :month mon :month-day d :hours h :minutes min :seconds s} (os/date)]
    (string y "-" (+ 1 mon) "-" (+ 1 d) "T" h ":" min ":" s)))

(def a @[1 2])
(def b @[1 2])
(= a b)  # => false

(def a @[1 2])
(def b (array/concat a 3))
a        # => @[1 2 3]
b        # => @[1 2 3]
(= a b)  # => true

(get default-peg-grammar :h)
# => '(range "09" "af" "AF")

(cmp [1 2] [1 2 3])
# => -1

(var x 1)
(loop [n :range-to [1 5]]
  (*= x n))
x # => 120

(import joy)

# given a handler
(defn handle-func [request]
  (joy/text/plain (string "Hi " ((request :params) :name))))

# joy/routes will make handlers
(def r (joy/routes [:get "/hi/:name" :handle-func]))
# which you can pass to joy/app
(joy/server (joy/app {:routes r}) 9002)
# visit at localhost:9002/hi/bob

(pairs {:a 1 :b 2 :c 3})
# =>
@[(:c 3) (:a 1) (:b 2)]

## Quadratic Formula

(defn qform
  "Use the quadratic formula to solve for x. Returns all real solutions."
  [a b c]
  (def det (- (* b b) (* 4 a c)))
  (def factor (/ 0.5 a))
  (cond
    (neg? det) []
    (zero? det) [(* factor (- b))]
    (let [root-det (math/sqrt det)]
        [(* factor (- (- b) root-det)) (* factor (+ (- b) root-det))])))

    (qform 1 4 3) # -> (-3 -1)

(<)        # -> true
(< 1)      # -> true
(< 1 2)    # -> true
(< 2 1)    # -> false
(< 1 2 3)  # -> true
(< 1 3 2)  # -> false