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# Just like its CoffeeScript cousin, LiveScript uses hash symbols for
# single-line comments.

/*
 Multi-line comments are written C-style. Use them if you want comments
 to be preserved in the JavaScript output.
 */

# As far as syntax goes, LiveScript uses indentation to delimit blocks,
# rather than curly braces, and whitespace to apply functions, rather
# than parenthesis.


########################################################################
## 1. Basic values
########################################################################

# Lack of value is defined by the keyword `void` instead of `undefined`
void            # same as `undefined` but safer (can't be overridden)

# No valid value is represented by Null.
null


# The most basic actual value is the logical type:
true
false

# And it has a plethora of aliases that mean the same thing:
on; off
yes; no


# Then you get numbers. These are double-precision floats like in JS.
10
0.4     # Note that the leading `0` is required

# For readability, you may use underscores and letter suffixes in a
# number, and these will be ignored by the compiler.
12_344km


# Strings are immutable sequences of characters, like in JS:
"Christina"             # apostrophes are okay too!
"""Multi-line
   strings
   are
   okay
   too."""

# Sometimes you want to encode a keyword, the backslash notation makes
# this easy:
\keyword                # => 'keyword'


# Arrays are ordered collections of values.
fruits =
  * \apple
  * \orange
  * \pear

# They can be expressed more concisely with square brackets:
fruits = [ \apple, \orange, \pear ]

# You also get a convenient way to create a list of strings, using
# white space to delimit the items.
fruits = <[ apple orange pear ]>

# You can retrieve an item by their 0-based index:
fruits[0]       # => "apple"

# Objects are a collection of unordered key/value pairs, and a few other
# things (more on that later).
person =
  name: "Christina"
  likes:
    * "kittens"
    * "and other cute stuff"

# Again, you can express them concisely with curly brackets:
person = {name: "Christina", likes: ["kittens", "and other cute stuff"]}

# You can retrieve an item by their key:
person.name     # => "Christina"
person["name"]  # => "Christina"


# Regular expressions use the same syntax as JavaScript:
trailing-space = /\s$/          # dashed-words become dashedWords

# Except you can do multi-line expressions too!
# (comments and whitespace just gets ignored)
funRE = //
        function\s+(.+)         # name
        \s* \((.*)\) \s*        # arguments
        { (.*) }                # body
        //


########################################################################
## 2. Basic operations
########################################################################

# Arithmetic operators are the same as JavaScript's:
1 + 2   # => 3
2 - 1   # => 1
2 * 3   # => 6
4 / 2   # => 2
3 % 2   # => 1


# Comparisons are mostly the same too, except that `==` and `===` are
# inverted.
2 == 2          # => true
2 == "2"        # => false
2 === "2"       # => true

# Other relational operators include <, <=, > and >=

# Logical values can be combined through the logical operators `or`,
# `and` and `not`
true and false  # => false
false or true   # => true
not false       # => true


# Collections also get some nice additional operators
[1, 2] ++ [3, 4]                # => [1, 2, 3, 4]
'a' in <[ a b c ]>              # => true
'name' of { name: 'Chris' }     # => true


########################################################################
## 3. Functions
########################################################################        

# Since LiveScript is functional, you'd expect functions to get a nice
# treatment. In LiveScript it's even more apparent that functions are
# first class:
add = (left, right) -> left + right
add 1, 2        # => 3

# Functions which take no arguments are called with a bang!
two = -> 2
two!

# LiveScript uses function scope, just like JavaScript, and has proper
# closures too. Unlike JavaScript, the `=` works as a declaration
# operator, and will always declare the variable on the left hand side.

# The `:=` operator is available to *reuse* a name from the parent
# scope.


# You can destructure arguments of a function to quickly get to
# interesting values inside a complex data structure:
tail = ([head, ...rest]) -> rest
tail [1, 2, 3]  # => [2, 3]

# You can also transform the arguments using binary or unary
# operators. Default arguments are also possible.
foo = (a = 1, b = 2) -> a + b
foo!    # => 3

# You could use it to clone a particular argument to avoid side-effects,
# for example:
copy = (^^target, source) ->
  for k,v of source => target[k] = v
  target
a = { a: 1 }
copy a, { b: 2 }        # => { a: 1, b: 2 }
a                       # => { a: 1 }


# A function may be curried by using a long arrow rather than a short
# one:
add = (left, right) --> left + right
add1 = add 1
add1 2          # => 3

# Functions get an implicit `it` argument, even if you don't declare
# any.
identity = -> it
identity 1      # => 1

# Operators are not functions in LiveScript, but you can easily turn
# them into one! Enter the operator sectioning:
divide-by-2 = (/ 2)
[2, 4, 8, 16].map(divide-by-2) .reduce (+)


# Not only of function application lives LiveScript, as in any good
# functional language you get facilities for composing them:
double-minus-one = (- 1) . (* 2)

# Other than the usual `f . g` mathematical formulae, you get the `>>`
# and `<<` operators, that describe how the flow of values through the
# functions. 
double-minus-one = (* 2) >> (- 1)
double-minus-one = (- 1) << (* 2)


# And talking about flow of value, LiveScript gets the `|>` and `<|`
# operators that apply a value to a function:
map = (f, xs) --> xs.map f
[1 2 3] |> map (* 2)            # => [2 4 6]

# You can also choose where you want the value to be placed, just mark
# the place with an underscore (_):
reduce = (f, xs, initial) --> xs.reduce f, initial
[1 2 3] |> reduce (+), _, 0     # => 6


# The underscore is also used in regular partial application, which you
# can use for any function:
div = (left, right) -> left / right
div-by-2 = div _, 2
div-by-2 4      # => 2


# Last, but not least, LiveScript has back-calls, which might help
# with some callback-based code (though you should try more functional
# approaches, like Promises):
readFile = (name, f) -> f name
a <- readFile 'foo'
b <- readFile 'bar'
console.log a + b

# Same as:
readFile 'foo', (a) -> readFile 'bar', (b) -> console.log a + b


########################################################################
## 4. Patterns, guards and control-flow
########################################################################

# You can branch computations with the `if...else` expression:
x = if n > 0 then \positive else \negative

# Instead of `then`, you can use `=>`
x = if n > 0 => \positive
    else        \negative

# Complex conditions are better-off expressed with the `switch`
# expression, though:
y = {}
x = switch
  | (typeof y) is \number => \number
  | (typeof y) is \string => \string
  | 'length' of y         => \array
  | otherwise             => \object      # `otherwise` and `_` always matches.

# Function bodies, declarations and assignments get a free `switch`, so
# you don't need to type it again:
take = (n, [x, ...xs]) -->
                        | n == 0 => []
                        | _      => [x] ++ take (n - 1), xs


########################################################################
## 5. Comprehensions
########################################################################

# While the functional helpers for dealing with lists and objects are
# right there in the JavaScript's standard library (and complemented on
# the prelude-ls, which is a "standard library" for LiveScript),
# comprehensions will usually allow you to do this stuff faster and with
# a nice syntax:
oneToTwenty = [1 to 20]
evens       = [x for x in oneToTwenty when x % 2 == 0]

# `when` and `unless` can be used as filters in the comprehension.

# Object comprehension works in the same way, except that it gives you
# back an object rather than an Array:
copy = { [k, v] for k, v of source }


########################################################################
## 4. OOP
########################################################################

# While LiveScript is a functional language in most aspects, it also has
# some niceties for imperative and object oriented programming. One of
# them is class syntax and some class sugar inherited from CoffeeScript:
class Animal
  (@name, kind) ->
    @kind = kind
  action: (what) -> "*#{@name} (a #{@kind}) #{what}*"

class Cat extends Animal
  (@name) -> super @name, 'cat'
  purr: -> @action 'purrs'

kitten = new Cat 'Mei'
kitten.purr!      # => "*Mei (a cat) purrs*"

# Besides the classical single-inheritance pattern, you can also provide
# as many mixins as you would like for a class. Mixins are just plain
# objects:
Huggable =
  hug: -> @action 'is hugged'

class SnugglyCat extends Cat implements Huggable

kitten = new SnugglyCat 'Purr'
kitten.hug!     # => "*Mei (a cat) is hugged*"