;; this gives an gentle introduction to hy for a quick trial head to
;; http://try-hy.appspot.com
;;
; Semicolon comments, like other LISPS
;; s-expression basics
; lisp programs are made of symbolic expressions or sexps which
; resemble
(some-function args)
; now the quintessential hello world
(print "hello world")
;; simple data types
; All simple data types are exactly similar to their python counterparts
; which
42 ; => 42
3.14 ; => 3.14
True ; => True
4+10j ; => (4+10j) a complex number
; lets start with some really simple arithmetic
(+ 4 1) ;=> 5
; the operator is applied to all arguments, like other lisps
(+ 4 1 2 3) ;=> 10
(- 2 1) ;=> 1
(* 4 2) ;=> 8
(/ 4 1) ;=> 4
(% 4 2) ;=> 0 the modulo operator
; power is represented by ** operator like python
(** 3 2) ;=> 9
; nesting forms will do the expected thing
(+ 2 (* 4 2)) ;=> 10
; also logical operators and or not and equal to etc. do as expected
(= 5 4) ;=> False
(not (= 5 4)) ;=> True
;; variables
; variables are set using setv, variable names can use utf-8 except
; for ()[]{}",'`;#|
(setv a 42)
(setv π 3.14159)
(def *foo* 42)
;; other container data types
; strings, lists, tuples & dicts
; these are exactly same as python's container types
"hello world" ;=> "hello world"
; string operations work similar to python
(+ "hello " "world") ;=> "hello world"
; lists are created using [], indexing starts at 0
(setv mylist [1 2 3 4])
; tuples are immutable data structures
(setv mytuple (, 1 2))
; dictionaries are key value pairs
(setv dict1 {"key1" 42 "key2" 21})
; :name can be used to define keywords in hy which can be used for keys
(setv dict2 {:key1 41 :key2 20})
; use `get' to get the element at an index/key
(get mylist 1) ;=> 2
(get dict1 "key1") ;=> 42
; Alternatively if keywords were used they can directly be called
(:key1 dict2) ;=> 41
;; functions and other program constructs
; functions are defined using defn, the last sexp is returned by default
(defn greet [name]
"A simple greeting" ; an optional docstring
(print "hello " name))
(greet "bilbo") ;=> "hello bilbo"
; functions can take optional arguments as well as keyword arguments
(defn foolists [arg1 &optional [arg2 2]]
[arg1 arg2])
(foolists 3) ;=> [3 2]
(foolists 10 3) ;=> [10 3]
; you can use rest arguments and kwargs too:
(defn something-fancy [wow &rest descriptions &kwargs props]
(print "Look at" wow)
(print "It's" descriptions)
(print "And it also has:" props))
(something-fancy "My horse" "amazing" :mane "spectacular")
; you use apply instead of the splat operators:
(apply something-fancy ["My horse" "amazing"] { "mane" "spectacular" })
; anonymous functions are created using `fn' or `lambda' constructs
; which are similar to `defn'
(map (fn [x] (* x x)) [1 2 3 4]) ;=> [1 4 9 16]
;; Sequence operations
; hy has some builtin utils for sequence operations etc.
; retrieve the first element using `first' or `car'
(setv mylist [1 2 3 4])
(setv mydict {"a" 1 "b" 2})
(first mylist) ;=> 1
; slice lists using slice
(slice mylist 1 3) ;=> [2 3]
; or, in hy 0.11, use cut instead:
(cut mylist 1 3) ;=> [2 3]
; get elements from a list or dict using `get'
(get mylist 1) ;=> 2
(get mydict "b") ;=> 2
; list indexing starts from 0 same as python
; assoc can set elements at keys/indexes
(assoc mylist 2 10) ; makes mylist [1 2 10 4]
(assoc mydict "c" 3) ; makes mydict {"a" 1 "b" 2 "c" 3}
; there are a whole lot of other core functions which makes working with
; sequences fun
;; Python interop
;; import works just like in python
(import datetime)
(import [functools [partial reduce]]) ; imports fun1 and fun2 from module1
(import [matplotlib.pyplot :as plt]) ; doing an import foo as bar
; all builtin python methods etc. are accessible from hy
; a.foo(arg) is called as (.foo a arg)
(.split (.strip "hello world ")) ;=> ["hello" "world"]
; there is a shortcut for executing multiple functions on a value called the
; "threading macro", denoted by an arrow:
(-> "hello world " (.strip) (.split)) ;=> ["hello" "world]
; the arrow passes the value along the calls as the first argument, for instance:
(-> 4 (* 3) (+ 2))
; is the same as:
(+ (* 4 3) 2)
; there is also a "threading tail macro", which instead passes the value as the
; second argument. compare:
(-> 4 (- 2) (+ 1)) ;=> 3
(+ (- 4 2) 1) ;=> 3
; to:
(->> 4 (- 2) (+ 1)) ;=> -1
(+ 1 (- 2 4)) ;=> -1
;; Conditionals
; (if condition (body-if-true) (body-if-false)
(if (= passcode "moria")
(print "welcome")
(print "Speak friend, and Enter!"))
; nest multiple if else if clauses with cond
(cond
[(= someval 42)
(print "Life, universe and everything else!")]
[(> someval 42)
(print "val too large")]
[(< someval 42)
(print "val too small")])
; group statements with do, these are executed sequentially
; forms like defn have an implicit do
(do
(setv someval 10)
(print "someval is set to " someval)) ;=> 10
; create lexical bindings with `let', all variables defined thusly
; have local scope
(let [[nemesis {"superman" "lex luther"
"sherlock" "moriarty"
"seinfeld" "newman"}]]
(for [(, h v) (.items nemesis)]
(print (.format "{0}'s nemesis was {1}" h v))))
;; classes
; classes are defined in the following way
(defclass Wizard [object]
[[--init-- (fn [self spell]
(setv self.spell spell) ; init the spell attr
None)]
[get-spell (fn [self]
self.spell)]])
; or, in hy 0.11:
(defclass Wizard [object]
(defn --init-- [self spell]
(setv self.spell spell))
(defn get-spell [self]
self.spell))
;; do checkout hylang.org
Last modified 06 April 2022