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|
# A more complex parser that illustrates how a compiler might be constructed.
# The parser recognizes strings and integer literals and constructs almost a
# useful AST from the file contents.
require 'pp'
$:.unshift File.dirname(__FILE__) + "/../lib"
require 'parslet'
include Parslet
class LiteralsParser < Parslet::Parser
rule :space do
(match '[ ]').repeat(1)
end
rule :literals do
(literal >> eol).repeat
end
rule :literal do
(integer | string).as(:literal) >> space.maybe
end
rule :string do
str('"') >>
(
(str('\\') >> any) |
(str('"').absent? >> any)
).repeat.as(:string) >>
str('"')
end
rule :integer do
match('[0-9]').repeat(1).as(:integer)
end
rule :eol do
line_end.repeat(1)
end
rule :line_end do
crlf >> space.maybe
end
rule :crlf do
match('[\r\n]').repeat(1)
end
root :literals
end
input_name = File.join(File.dirname(__FILE__), 'simple.lit')
file = File.read(input_name)
parsetree = LiteralsParser.new.parse(file)
class Lit < Struct.new(:text)
def to_s
text.inspect
end
end
class StringLit < Lit
end
class IntLit < Lit
def to_s
text
end
end
transform = Parslet::Transform.new do
rule(:literal => {:integer => simple(:x)}) { IntLit.new(x) }
rule(:literal => {:string => simple(:s)}) { StringLit.new(s) }
end
ast = transform.apply(parsetree)
pp ast
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