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Sean Walker

Janet Basics

; # A pound sign (or hashtag) starts a one-line comment.
; # I'm using clojure's ; comments because chroma doesn't support janet
  Wrapping something in the
  comment form makes a multiline comment)

Variables and flow control

(def num 42) ; # All numbers are double precision floating point numbers

"A few more numbers"

(def num1 10_000) ; # you can use underscores as decimal places, like ruby

(def s "the good place") ; # Immutable strings
(def s `Backticks
        start/end multine strings`) ; # backticks for multiline strings
(def t nil) ; # nil is a thing

; # loops can be done with either map, loop or while
(while (< i 50)
  (++ i))

; # If clauses:
(if (> num 40)
  (print "over 40")
    (if (not= s "the good place")
      (print "not over 40")       ; # you don't need a second form necessarily
    (var this-is-local 5))))      ; # variables are lexically scoped by default

; # How to make a variable global (to a file)
; # outside of any do's or any loops or anything
(var x "im global")

; # String concatentation uses the (string) or (print) forms

(string "winter is coming " "quickly") ; # => "winter is coming quickly"
(print "winter is coming" "quickly") ; # => "winter is comingquickly"

; # Undefined variables throw errors.
; # This is an error:
(def x an-unknown-variable) ; # => compile error: unknown symbol an-unknown-variable while compiling repl

(def a-bool-value false)

; # nil and false are falsy, 0 and "" are not!
(when (not aBoolValue) (print "twas false"))

; # 'or' and 'and' are short-circuited.
(def ans (or (and a-bool-value "yes") "no")) ; # => "no"

(var a-sum 0)
(for i 1 100 ; # the range does NOT include both ends
  (+= a-sum i))

; # Another loop construct:
(var sum 0)
(loop [i :range [0 10] :when (even? i)] (+= sum i))
(print sum) ; # prints 20


Check out the official docs for more info, and be sure to check out the gitter channel if you have any questions or just want to say hi.

There’s also janet docs which is a very unofficial community docs site I put together with the joy web framework that I also put together.

I’ll update this post with more examples in the vein of eventually.