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# frozen_string_literal: true
require_relative 'scanner'
require_relative 'grammar'
require_relative '../ast/ast_builder'
module Loxxy
module FrontEnd
# A Lox parser that produce concrete parse trees.
# Concrete parse trees are the default kind of parse tree
# generated by the Rley library.
# They consist of two node types only:
# - NonTerminalNode
# - TerminalNode
# A NonTerminalNode has zero or more child nodes (called subnodes)
# A TerminalNode is leaf node, that is, it has no child node.
# While concrete parse tree nodes can be generated out of the box,
# they have the following drawbacks:
# - Generic node classes that aren't always suited for the needs of
# the language being processing.
# - Concrete parse tree tend to be deeply nested, which may complicate
# further processing.
class Parser
# @return [Rley::Engine] A facade object for the Rley parsing library
attr_reader(:engine)
def initialize
# Create a Rley facade object
@engine = Rley::Engine.new do |cfg|
cfg.diagnose = true
cfg.repr_builder = Ast::ASTBuilder
end
# Step 1. Load Lox grammar
@engine.use_grammar(Loxxy::FrontEnd::Grammar)
end
# Parse the given Lox program into a parse tree.
# @param source [String] Lox program to parse
# @return [Rley::ParseTree] A parse tree equivalent to the Lox input.
def parse(source)
lexer = Scanner.new(source)
result = engine.parse(lexer.tokens)
unless result.success?
# Stop if the parse failed...
line1 = "Parsing failed\n"
line2 = "Reason: #{result.failure_reason.message}"
raise StandardError, line1 + line2
end
return engine.convert(result) # engine.to_ptree(result)
end
end # class
end # module
end # module
Version data entries
45 entries across 45 versions & 1 rubygems