Class: Crapshoot::Postfixer

Inherits:
Object
  • Object
show all
Defined in:
lib/crapshoot/postfixer.rb

Overview

Translate the infix-notation tokens into postfix notation to make evaluating them easier.

Instance Method Summary collapse

Instance Method Details

#postfixify(infix_tokens) ⇒ Object

Postfixify turns the infix list of tokens from Scanner into a postfix list by repeatedly calling “step”



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# File 'lib/crapshoot/postfixer.rb', line 7

def postfixify(infix_tokens)
  @infix_orig = infix_tokens
  @infix = @infix_orig.dup
  @postfix = []
  @operator_stack = []
  until @infix.empty?
    step
  end

  until @operator_stack.empty?
    @postfix.push @operator_stack.pop
  end

  return @postfix
end

#process_independent(candidate) ⇒ Object 



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# File 'lib/crapshoot/postfixer.rb', line 32

def process_independent(candidate)
  return unless candidate.independent
  @postfix.push candidate
end

#process_operator(candidate) ⇒ Object 



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# File 'lib/crapshoot/postfixer.rb', line 37

def process_operator(candidate)
  return if candidate.independent

  if @operator_stack.empty? || candidate.precedent(@operator_stack.last)
    @operator_stack.push candidate
  else
    @postfix.push @operator_stack.pop
    @operator_stack.push candidate
  end
end

#step ⇒ Object

step shifts an independent (Constant or Series) token to the postfix list, or loads a dependent (Arithmetic) token into the operator_stack for future postfixing.



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# File 'lib/crapshoot/postfixer.rb', line 26

def step
  candidate = @infix.shift
  process_independent candidate
  process_operator candidate
end