`class Evaluator`

Represents a lazy evaluator that resolves and caches environment values on demand.

Definitions

`def initialize(environment)`

Initialize the evaluator with an environment.

Signature

parameter　environment　Environment: The environment whose values will be evaluated.

Implementation

def initialize(environment)
	@environment = environment
	@cache = {}
end

`def initialize_dup(other)`

Copy the environment reference and cache when duplicating.

Signature

parameter　other　Evaluator: The evaluator being duplicated.

Implementation

def initialize_dup(other)
	@environment = other.instance_variable_get(:@environment)
	@cache = other.instance_variable_get(:@cache).dup
	
	super
end

`def respond_to?(name, include_private = false)`

Check whether the evaluator responds to a given method name.

Signature

parameter　name　Symbol: The method name to check.
parameter　include_private　Boolean: Whether to include private methods.
returns　Boolean: true if the environment contains the key or the evaluator responds via super.

Implementation

def respond_to?(name, include_private = false)
	@environment.include?(name) || super
end

`def method_missing(name)`

Evaluate and cache the value for the named key.

Signature

parameter　name　Symbol: The key to resolve from the environment.
returns　Object: The resolved and cached value.

Implementation

def method_missing(name)
	@cache[name] ||= object_value(@environment[name])
end

`def object_value(value)`

Compute the literal object value for a given key:

Implementation

def object_value(value)
	case value
	when Array
		value.collect{|item| object_value(item)}.flatten
	when Symbol
		object_value(@environment[value])
	when Proc
		object_value(instance_exec(&value))
	when Default
		object_value(value.value)
	when Replace
		object_value(value.value)
	else
		value
	end
end