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scope.coffee

The Scope class regulates lexical scoping within CoffeeScript. As you generate code, you create a tree of scopes in the same shape as the nested function bodies. Each scope knows about the variables declared within it, and has a reference to its parent enclosing scope. In this way, we know which variables are new and need to be declared with var, and which are shared with the outside.

Import the helpers we plan to use.

{extend, last} = require './helpers'

exports.Scope = class Scope

The top-level Scope object.

  @root: null

Initialize a scope with its parent, for lookups up the chain, as well as a reference to the Expressions node is belongs to, which is where it should declare its variables, and a reference to the function that it wraps.

  constructor:(@parent, @expressions, @method) ->
    @variables = [{name: 'arguments', type: 'arguments'}]
    @positions = {}
    Scope.root = this unless @parent

Adds a new variable or overrides an existing one.

  add: (name, type) ->
    if typeof (pos = @positions[name]) is 'number'
      @variables[pos].type = type
    else
      @positions[name] = @variables.push({name, type}) - 1

Look up a variable name in lexical scope, and declare it if it does not already exist.

  find: (name, options) ->
    return yes if @check name, options
    @add name, 'var'
    no

Reserve a variable name as originating from a function parameter for this scope. No var required for internal references.

  parameter: (name) ->
    return if @shared and @check name, yes
    @add name, 'param'

Just check to see if a variable has already been declared, without reserving, walks up to the root scope.

  check: (name, immediate) ->
    found = !!@type(name)
    return found if found or immediate
    !!@parent?.check name

Generate a temporary variable name at the given index.

  temporary: (name, index) ->
    if name.length > 1
      '_' + name + if index > 1 then index else ''
    else
      '_' + (index + parseInt name, 36).toString(36).replace /\d/g, 'a'

Gets the type of a variable.

  type: (name) ->
    return v.type for v in @variables when v.name is name
    null

If we need to store an intermediate result, find an available name for a compiler-generated variable. _var, _var2, and so on...

  freeVariable: (type) ->
    index = 0
    index++ while @check((temp = @temporary type, index), true)
    @add temp, 'var'
    temp

Ensure that an assignment is made at the top of this scope (or at the top-level scope, if requested).

  assign: (name, value) ->
    @add name, value: value, assigned: true
    @hasAssignments = yes

Does this scope have any declared variables?

  hasDeclarations: ->
    !!@declaredVariables().length

Return the list of variables first declared in this scope.

  declaredVariables: ->
    realVars = []
    tempVars = []
    for v in @variables when v.type is 'var'
      (if v.name.charAt(0) is '_' then tempVars else realVars).push v.name
    realVars.sort().concat tempVars.sort()

Return the list of assignments that are supposed to be made at the top of this scope.

  assignedVariables: ->
    "#{v.name} = #{v.type.value}" for v in @variables when v.type.assigned