LiveScript

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For the primary web scripting language initially known as LiveScript, see JavaScript.
LiveScript
Paradigm multi-paradigm, functional, object-oriented
Designed by Jeremy Ashkenas, Satoshi Murakami, George Zahariev
Developer Jeremy Ashkenas, Satoshi Murakami, George Zahariev
Appeared in 2011; 4 years ago (2011)
LiveScript 1.3.1 / 22 October 2014; 4 months ago (2014-10-22)
dynamic, weak, strong
OS Cross-platform
License MIT
.ls
Website livescript.net

LiveScript is a functional language that compiles to JavaScript.

Syntax[edit]

LiveScript is an indirect descendant of and is partly compatible with Coffeescript.[1] The following is a fully Coffeescript-compatible hello-world example of LiveScript syntax.

hello = ->
  console.log 'hello, world!'

While calling a function can be done with empty parens, hello(), LiveScript treats the exclamation mark as a single-character shorthand for function calls with zero arguments: hello!

LiveScript introduces a number of other incompatible idioms:

Name mangling[edit]

At compile time, the LiveScript parser implicitly converts dashed variable- and function names to camelcase.

hello-world = ->
  console.log 'Hello, World!'

With this definition, both the following calls are valid. However, calling using the same dashed syntax is recommended.

hello-world!
helloWorld!

This does not preclude developers from using camelcase explicitly or using snakecase. Dashed naming is however, common in idiomatic LiveScript[2]

Pipes[edit]

Like a number of other functional programming languages such as F# and Elixir, LiveScript supports the pipe operator, |> which passes the result of the expression on the left of the operator as the first argument to the expression on the right of it.

hello! |> capitalize |> console.log
# > Hello, World!

Operators as functions[edit]

When parenthesized, operators such as not or + can be included in pipelines or called as if they were functions.

111 |> (+) 222
# > 333
 
(+) 1 2
# > 3

Typing[edit]

By default, LiveScript shares the weak, dynamic typing of Coffee- and JavaScript. However, the LiveScript compiler provides optional strong typing through the --const flag.

num = 1
fun = (non-string) ->
  non-string = non-string.to-string!
fun num

While perfectly permissible by default, when the --const flag is used, the above will cause a compiler error of: [SyntaxError: redeclaration of constant "num" on line 4]. This happens because the --const option simply treats all values as if they were declared as constants, at compile time, without using the not widely supported const keyword in the output JavaScript.

References[edit]

External links[edit]