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diff --git a/livescript.html.markdown b/livescript.html.markdown new file mode 100644 index 00000000..2c72df0a --- /dev/null +++ b/livescript.html.markdown @@ -0,0 +1,344 @@ +--- +language: LiveScript +filename: learnLivescript.ls +contributors: + - ["Christina Whyte", "http://github.com/kurisuwhyte/"] +--- + +LiveScript is a functional compile-to-JavaScript language which shares +most of the underlying semantics with its host language. Nice additions +comes with currying, function composition, pattern matching and lots of +other goodies heavily borrowed from languages like Haskell, F# and +Scala. + +LiveScript is a fork of [Coco][], which is itself a fork of +[CoffeeScript][]. The language is stable, and a new version is in active +development to bring a plethora of new niceties! + +[Coco]: http://satyr.github.io/coco/ +[CoffeeScript]: http://coffeescript.org/ + +Feedback is always welcome, so feel free to reach me over at +[@kurisuwhyte](https://twitter.com/kurisuwhyte) :) + + +```livescript +# 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*" +``` + +## Further reading + +There's just so much more to LiveScript, but this should be enough to +get you started writing little functional things in it. The +[official website](http://livescript.net/) has a lot of information on the +language, and a nice online compiler for you to try stuff out! + +You may also want to grab yourself some +[prelude.ls](http://gkz.github.io/prelude-ls/), and check out the `#livescript` +channel on the Freenode network. |