Class: Parslet::Atoms::Alternative

Inherits:
Base
  • Object
show all
Defined in:
lib/parslet/atoms/alternative.rb,
lib/parslet/atoms/visitor.rb

Overview

Alternative during matching. Contains a list of parslets that is tried each one in turn. Only fails if all alternatives fail.

Example: 

str('a') | str('b')   # matches either 'a' or 'b'

Constant Summary

Constants included from Precedence

Precedence::ALTERNATE, Precedence::BASE, Precedence::LOOKAHEAD, Precedence::OUTER, Precedence::REPETITION, Precedence::SEQUENCE

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods inherited from Base

#apply, #inspect, #parse, #parse_with_debug, precedence, #setup_and_apply, #to_s

Methods included from CanFlatten

#flatten, #flatten_repetition, #flatten_sequence, #foldl, #merge_fold, #warn_about_duplicate_keys

Methods included from DSL

#>>, #absent?, #as, #maybe, #present?, #repeat

Constructor Details

#initialize(*alternatives) ⇒ Alternative

Constructs an Alternative instance using all given parslets in the order given. This is what happens if you call ‘|’ on existing parslets, like this: 

str('a') | str('b')



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# File 'lib/parslet/atoms/alternative.rb', line 18

def initialize(*alternatives)
  super()
  
  @alternatives = alternatives
  @error_msg = "Expected one of #{alternatives.inspect}"
end

Instance Attribute Details

#alternatives ⇒ Object (readonly)

Returns the value of attribute alternatives.



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# File 'lib/parslet/atoms/alternative.rb', line 10

def alternatives
  @alternatives
end

Instance Method Details

#accept(visitor) ⇒ Object

Call back visitors #visit_alternative method. See parslet/export for an example.



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# File 'lib/parslet/atoms/visitor.rb', line 60

def accept(visitor)
  visitor.visit_alternative(alternatives)
end

#to_s_inner(prec) ⇒ Object 



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# File 'lib/parslet/atoms/alternative.rb', line 47

def to_s_inner(prec)
  alternatives.map { |a| a.to_s(prec) }.join(' / ')
end

#try(source, context) ⇒ Object 



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# File 'lib/parslet/atoms/alternative.rb', line 33

def try(source, context)
  errors = alternatives.map { |a|
    success, value = result = a.apply(source, context)
    return result if success
    
    # Aggregate all errors
    value
  }
  
  # If we reach this point, all alternatives have failed. 
  context.err(self, source, @error_msg, errors)
end

#|(parslet) ⇒ Object

Don’t construct a hanging tree of Alternative parslets, instead store them all here. This reduces the number of objects created. +++



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# File 'lib/parslet/atoms/alternative.rb', line 29

def |(parslet)
  self.class.new(*@alternatives + [parslet])
end