Janet

Janet is a functional (and imperative) cross-platform interpreted (and compiled) lisp-inspired language with batteries-included api that makes a good system scripting language, or a language to embed in other programs.

The entire language (core library, interpreter, compiler, assembler, PEG) is less than 1MB.

Resources

Official Site

Notes

Very Basics

Starting off with minimum required to do anything

Data Types:

Comments start with a #

nil
booleans: true, false
symbols (conventionally small-letters with hypens)
keywords: :symbols starting with colon
numbers: like javascript number 1 -1.1 1e10 (unlike js, 4r100 = 16: rn = base n)

Data Structures:

strings: "strings are in double quotes" or in n`s like lua’s [[ ... ]]
buffer: mutable @strings
tuples: [1 2 3] list of values
arrays: mutable @tuples
structs: like elixir’s {:keyword "value"} pairs (or js objects, or clisp plists)
tables: mutable @structs

Bindings:

anything with paren tuple (...) is “called” (conventionally called “forms”)

Variable definition: ([def | var] <name> <expr>)
- immutable def or mutable var
- bind any value retured by <expr> to a symbol <name>
- works as variable assignment but can also destructure (pattern match) on lists and dicts
- use (let [<name> <expr> <name2> <expr2>] ...) for multiple def bindings sugar
Variable reassignment: (set <name> <expr>)
- only works on var
- name must exists and be an initialized value or a declared datastructure
Function definition: ([defn | fn] [<name>] <args> <body>)
- yes, name is optional in case of fn. functions form closure.
- arguments are literal tuples [...] but can be destructured from structs
- use & for variadic arguments: [a b c & rest]
- body is zero or more forms (...)
- last form is returned implicitly
- defn is short for binding fn to <name> using def

Conditionals:

If conditional: (if <expr> <true-form> [<false-form>])
- lazy eval (does not evaluate forms until needed)
- if no false-form but cond is false, then returns nil
Cond conditional: (cond <expr> (body) <expr2> (body2) <expr3> (body3))
- Can be used instead of multiple if-else-if-else nesting
Case conditional:
- think switch statements elsewhere
When conditional:
- like if without false-form; returns nil on false implicitly

Loops:

OPINION: Avoiding mutable loops and stick to functional paradigm

While loop: (while <cond> <body>)
- Usually works with mutable vars with side effects in body
For loop: (for <var> <start-expr> <end-expr> <body>)
loop loop: (loop [<var> <verb> <values> <modifiers> <cond>] <body>)
- Ex1: (loop [i :range [0 10] :when (even? i)] (print i))
  - i is a var, :range is a verb, :when is a modifier
- Ex2: (loop [name :in names] (print name))
  - name is a var, :in is a verb and names is a list
- Ex2 can be written using each and map resp as:
  - (each name names (print name))
  - (map print names)
- Ex3: (loop [[k v] :pairs some_struct] (print k " -> " v))
  - Above for looping across a dict

Arithmetic (<op> <expr> <expr2>) and Comparisons (<cmp> <expr> <expr2>) work as usual:

Use (not= <expr> <expr2>) for checking unequality
Use (deep= <mutable> <mutable>) for checking contents of mutable structures