Community documentation for Janet

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

(math/hypot 1 1)  # => 1.41421
(math/sqrt 2)     # => 1.41421

(var abc 123)
(= 356 (with-vars [abc 456] (- abc 100)))

(peg/find-all ':d "hi 1 bye 2") # => @[3 9]

# 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: 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 [now (os/clock :realtime)
        ms (math/floor (* 1000 (mod now 1)))
        {:year y :month mon :month-day d :hours h :minutes min :seconds s}
        (os/date (math/floor now))]
    (string/format "%d-%02d-%02dT%02d:%02d:%02d.%03dZ" y (inc mon) (inc d) h min s ms)))

(def [pipe-r pipe-w] (os/pipe))
(:write pipe-w "hello")
(:read pipe-r 5)
# => @"hello"

# send the string "hello" into the writable stream
# part and read it back from the readable one

# absolute value of negatives, ignore positives
(keep |(if (< $ 0) (- $) nil) [-1 2 -3 -4 -5 6]) # -> @[1 3 4 5]

# halves each even number, ignores odds
(keep |(when (even? $) (/ $ 2)) [1 2 8 7 -2])    # -> @[1 4 -1]

# Some tips for working with bytes and unicode:
(string/bytes "что-нибудь")                         #> (209 135 209 130 208 190 45 208 189 208 184 ...
(print (string/from-bytes 208 176 208 177))         #> аб
(map string/from-bytes (string/bytes "что-нибудь")) #> @["\xD1" "\x87" "\xD1" "\x82" "\xD0" "\xBE" ...

# Print renders "\xD1" "\x87" as ч, as unicode characters may have multiple bytes
# So use apply:
(apply print (map string/from-bytes 
                  (string/bytes "что-нибудь")))     #> что-нибудь

(/ 2)
# => 0.5

(def cc (ev/thread-chan 99))  # Sets up a message channel.
(def ww (filewatch/new cc))   # Creates the watcher.
(filewatch/add ww "ftest.janet" :all)     # Watch for all changes.
(filewatch/add ww "fadd.janet"  :modify)  # Only care if modified (Linux-specific flag).
(filewatch/listen ww)         # Start filewatcher listening for changes.

(pp (ev/take cc))             # Print info on first file to change.
(filewatch/unlisten ww)       # Stop caring about changes.

(for i 0 5 
     (print i))
 
# 0
# 1
# 2
# 3
# 4

# => nil

(tabseq [i :in (range 97 100)]
  i (string/from-bytes i))
# =>
@{97 "a"
  98 "b"
  99 "c"}

(last "hello")
# => 111

# based on: https://codeberg.org/veqq/janetdocs/src/commit/54a964d1a35920af2655c4932a9b51379e8b9380/seed.janet#L16 

(def core-api (all-bindings))
(def alldocs @[])

(loop [b :in core-api]
  (when (not= "allbindings" (string b))
    (do
      (def buf @"")
      (with-dyns [:out buf]
        (doc* b)
        (array/push alldocs {:name (string b) :docstring (string buf)})))))

(pp alldocs)

(def a @[1 2])
(array/concat a 3 [4 5] @[6 7] [] @[] 8)
a  # => @[1 2 3 4 5 6 7 8]

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

(map inc
     (fiber/new |(each x (range 3)
                   (yield x))))
# => @[1 2 3]

(defmacro- =dude
 "sets any symbolic expression to the atom :what?"
 [a]
 ~(var a :what?)) # => <function =dude>

(=dude 2) # => :what?

(=dude :2) # => :what?

(=dude 2) # => :what?

(=dude "2") # => :what?

(=dude @"2") # => :what?

(=dude @[2]) # => :what?

(=dude (2)) # => :what?

(=dude [2]) # => :what?

(=dude @{2 3}) # => :what?


(doc =dude)


# =>    macro
# =>    repl on line 59, column 1
# =>
# =>    (=dude a)


# => nil


# Macro expanding the =dude macro:

(macex (=dude 2)) # => :what?

(macex1 (=dude 2)) # => :what?

# Macros have to be quoted in order to expand

(macex ~(=dude 2)) # => (var a :what?)

(macex1 ~(=dude 2)) # => (var a :what?)

(macex ~(=dude @{2 3})) # => (var a :what?)

(interpose 0 [1])
# -> @[1]

(let [p @{:a 1}
      t @{:b 2}]
  (table/setproto t p)
  [(get t :a) (table/rawget t :a)])
# => '(1 nil)