Cincle

This is an old pet project. I keep it for the sake of it. I used it here globoplox/dice.

Cincle is a layer added to the Lingo parser generator. It aim to help to build meaningfull ast by altering the parser, generating a default visitor, and extensibles nodes for each rules.

Installation

dependencies:
  cincle:
    github: globoplox/cincle

Usage

require "./cincle"

module Expression

 include Cincle

 node :number {
   def val
     raw.to_i
   end
 }

 node :operator {
   def apply(operands)
     operands.reduce { |a,b| plus? ? a + b : a - b }
   end
 }

 node :expression {
   def result
     operator.apply(numbers.map &.val)
   end
 }

 rule :number { match(/\d+/) }
 rule :plus { str("+") }
 rule :minus { str("-") }
 rule :operator { plus | minus }
 rule :expression { number >> operator >> number }

 root :expression
end

puts Expression.parse(ARGV[0]).result

Cincle rules are following the same pattern as Lingo (in fact, they are Lingo rules).
The node macro allow to define a custom body that will be inserted into the classes generated by Cincle. The root macro must be called after all nodes and rules have been defined.

Onion

The onion macro can be used to define union:

module Exemple
  include Cincle
  node :plus {
    def apply(a,b)
      a + b
    end
  }

  node :minus {
    def apply(a,b)
      a - b
    end
  }

  rule :plus { str "+" }
  rule :minus { str "-" }

  onion :operator, [:plus, :minus] {
    asbtract def apply
  }

  root :operator
end

Exemple.parse("-").apply(6,7)

How it works

For each rules, a custom node class will be generated. Each node contain a @nodes attribute containing all subnodes that have been created during the parsing of the associated rule. E.G. the Expression node will contain two Numbers node and an Operator node. Subnodes can be accessed from the @nodes : Hash(Symbol,Array(Node)) attribute, or from the helpers method <node_name>(index=0), <node_name>?(index=0) and <plural_node_name>.

The code generated by Cincle can be visualized by adding the --define debug_cincle to the crystal command.

Todo

Add a way to make node more typesafe, by removing accessor for nodes that cannot be subnodes of the current node. (E.G. Number#minus will raise at compile time, while Operator#minus wont).
Add a true pluralizer, and/or allow defining customs pluralizers (trail: DIR constant)

Development

TODO Write development instructions here

Contributors

Globoplox Pierre Rousselle - creator, maintainer

CrystalDoc.info

cincle