118 lines
3.8 KiB
Markdown
118 lines
3.8 KiB
Markdown
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The **Scope** class regulates lexical scoping within CoffeeScript. As you
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generate code, you create a tree of scopes in the same shape as the nested
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function bodies. Each scope knows about the variables declared within it,
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and has a reference to its parent enclosing scope. In this way, we know which
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variables are new and need to be declared with `var`, and which are shared
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with external scopes.
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Import the helpers we plan to use.
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{extend, last} = require './helpers'
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exports.Scope = class Scope
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The `root` is the top-level **Scope** object for a given file.
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@root: null
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Initialize a scope with its parent, for lookups up the chain,
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as well as a reference to the **Block** node it belongs to, which is
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where it should declare its variables, and a reference to the function that
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it belongs to.
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constructor: (@parent, @expressions, @method) ->
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@variables = [{name: 'arguments', type: 'arguments'}]
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@positions = {}
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Scope.root = this unless @parent
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Adds a new variable or overrides an existing one.
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add: (name, type, immediate) ->
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return @parent.add name, type, immediate if @shared and not immediate
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if Object::hasOwnProperty.call @positions, name
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@variables[@positions[name]].type = type
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else
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@positions[name] = @variables.push({name, type}) - 1
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When `super` is called, we need to find the name of the current method we're
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in, so that we know how to invoke the same method of the parent class. This
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can get complicated if super is being called from an inner function.
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`namedMethod` will walk up the scope tree until it either finds the first
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function object that has a name filled in, or bottoms out.
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namedMethod: ->
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return @method if @method.name or !@parent
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@parent.namedMethod()
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Look up a variable name in lexical scope, and declare it if it does not
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already exist.
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find: (name) ->
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return yes if @check name
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@add name, 'var'
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no
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Reserve a variable name as originating from a function parameter for this
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scope. No `var` required for internal references.
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parameter: (name) ->
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return if @shared and @parent.check name, yes
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@add name, 'param'
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Just check to see if a variable has already been declared, without reserving,
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walks up to the root scope.
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check: (name) ->
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!!(@type(name) or @parent?.check(name))
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Generate a temporary variable name at the given index.
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temporary: (name, index) ->
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if name.length > 1
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'_' + name + if index > 1 then index - 1 else ''
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else
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'_' + (index + parseInt name, 36).toString(36).replace /\d/g, 'a'
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Gets the type of a variable.
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type: (name) ->
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return v.type for v in @variables when v.name is name
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null
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If we need to store an intermediate result, find an available name for a
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compiler-generated variable. `_var`, `_var2`, and so on...
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freeVariable: (name, reserve=true) ->
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index = 0
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index++ while @check((temp = @temporary name, index))
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@add temp, 'var', yes if reserve
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temp
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Ensure that an assignment is made at the top of this scope
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(or at the top-level scope, if requested).
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assign: (name, value) ->
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@add name, {value, assigned: yes}, yes
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@hasAssignments = yes
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Does this scope have any declared variables?
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hasDeclarations: ->
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!!@declaredVariables().length
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Return the list of variables first declared in this scope.
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declaredVariables: ->
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realVars = []
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tempVars = []
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for v in @variables when v.type is 'var'
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(if v.name.charAt(0) is '_' then tempVars else realVars).push v.name
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realVars.sort().concat tempVars.sort()
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Return the list of assignments that are supposed to be made at the top
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of this scope.
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assignedVariables: ->
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"#{v.name} = #{v.type.value}" for v in @variables when v.type.assigned
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