Class: Smartdown::Parser::NodeTransform

Inherits:
Parslet::Transform
  • Object
show all
Defined in:
lib/smartdown/parser/node_transform.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(data_module = nil, &block) ⇒ NodeTransform

Returns a new instance of NodeTransform.



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# File 'lib/smartdown/parser/node_transform.rb', line 36

def initialize data_module=nil, &block
  super(&block)

  @data_module = data_module || {}
end

Instance Attribute Details

#data_module ⇒ Object (readonly)

Returns the value of attribute data_module.



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# File 'lib/smartdown/parser/node_transform.rb', line 34

def data_module
  @data_module
end

Instance Method Details

#call_on_match(bindings, block) ⇒ Object

!!ALERT!! MONKEY PATCHING !!ALERT!!

This call_on_match method is used for executing all the rule blocks you see below. The only variables that are in scope for these blocks are the contents of bindings - which consists of information about bits of the AST that the rule matched.

In the country rule: there is a need for accessing an external variable/method as the information required to create a country question object is defined in the data_module - so cannot be inferred purely from the syntax fed to parselet.

There are 2 options we could have chosen, the first would be to have another transformation layer. We would create intermediate elements that were lacking information and then recreate them outside of parselet.

A far simpler option is to manually modify the set of bindings available to rule blocks, so we can inject our information from the data_module. Unfortunately the only way to do this is to Monkey patch the call_on_match method to do the to injecting. The drawbacks of this are if the method changes its name or function in a newer parselet version; or possibly accidentally overriding some default bindings with methods from a data module.

Ideally we would like a way of injecting information into bindings without this patch so we have submitted a PR to parselet describing this problem:

github.com/kschiess/parslet/pull/119



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# File 'lib/smartdown/parser/node_transform.rb', line 69

def call_on_match(bindings, block)
  bindings.merge! data_module
  super(bindings, block)
end