Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

152 lines (130 sloc) 4.932 kb
# Base class for all parslets, handles orchestration of calls and implements
# a lot of the operator and chaining methods.
#
# Also see Parslet::Atoms::DSL chaining parslet atoms together.
#
class Parslet::Atoms::Base
include Parslet::Atoms::Precedence
include Parslet::Atoms::DSL
include Parslet::Atoms::CanFlatten
# Given a string or an IO object, this will attempt a parse of its contents
# and return a result. If the parse fails, a Parslet::ParseFailed exception
# will be thrown.
#
# @param io [String, Source] input for the parse process
# @option options [Parslet::ErrorReporter] :reporter error reporter to use,
# defaults to Parslet::ErrorReporter::Tree
# @option options [Boolean] :prefix Should a prefix match be accepted?
# (default: false)
# @return [Hash, Array, Parslet::Slice] PORO (Plain old Ruby object) result
# tree
#
def parse(io, options={})
source = io.respond_to?(:line_and_column) ?
io :
Parslet::Source.new(io)
# Try to cheat. Assuming that we'll be able to parse the input, don't
# run error reporting code.
success, value = setup_and_apply(source, nil, !options[:prefix])
# If we didn't succeed the parse, raise an exception for the user.
# Stack trace will be off, but the error tree should explain the reason
# it failed.
unless success
# Cheating has not paid off. Now pay the cost: Rerun the parse,
# gathering error information in the process.
reporter = options[:reporter] || Parslet::ErrorReporter::Tree.new
source.pos = 0
success, value = setup_and_apply(source, reporter, !options[:prefix])
fail "Assertion failed: success was true when parsing with reporter" \
if success
# Value is a Parslet::Cause, which can be turned into an exception:
value.raise
fail "NEVER REACHED"
end
# assert: success is true
# Extra input is now handled inline with the rest of the parsing. If
# really we have success == true, prefix: false and still some input
# is left dangling, that is a BUG.
if !options[:prefix] && source.chars_left > 0
fail "BUG: New error strategy should not reach this point."
end
return flatten(value)
end
# Creates a context for parsing and applies the current atom to the input.
# Returns the parse result.
#
# @return [<Boolean, Object>] Result of the parse. If the first member is
# true, the parse has succeeded.
def setup_and_apply(source, error_reporter, consume_all)
context = Parslet::Atoms::Context.new(error_reporter)
apply(source, context, consume_all)
end
# Calls the #try method of this parslet. Success consumes input, error will
# rewind the input.
#
# @param source [Parslet::Source] source to read input from
# @param context [Parslet::Atoms::Context] context to use for the parsing
# @param consume_all [Boolean] true if the current parse must consume
# all input by itself.
def apply(source, context, consume_all=false)
old_pos = source.pos
success, value = result = context.try_with_cache(self, source, consume_all)
if success
# If a consume_all parse was made and doesn't result in the consumption
# of all the input, that is considered an error.
if consume_all && source.chars_left>0
# Read 10 characters ahead. Why ten? I don't know.
offending_pos = source.pos
offending_input = source.consume(10)
# Rewind input (as happens always in error case)
source.pos = old_pos
return context.err_at(
self,
source,
"Don't know what to do with #{offending_input.to_s.inspect}",
offending_pos
)
end
# Looks like the parse was successful after all. Don't rewind the input.
return result
end
# We only reach this point if the parse has failed. Rewind the input.
source.pos = old_pos
return result
end
# Override this in your Atoms::Base subclasses to implement parsing
# behaviour.
#
def try(source, context, consume_all)
raise NotImplementedError, \
"Atoms::Base doesn't have behaviour, please implement #try(source, context)."
end
# Returns true if this atom can be cached in the packrat cache. Most parslet
# atoms are cached, so this always returns true, unless overridden.
#
def cached?
true
end
# Debug printing - in Treetop syntax.
#
def self.precedence(prec)
define_method(:precedence) { prec }
end
precedence BASE
def to_s(outer_prec=OUTER)
if outer_prec < precedence
"("+to_s_inner(precedence)+")"
else
to_s_inner(precedence)
end
end
def inspect
to_s(OUTER)
end
private
# Produces an instance of Success and returns it.
#
def succ(result)
[true, result]
end
end
Jump to Line
Something went wrong with that request. Please try again.