From: James Edward Gray II <james@...>
Date: 2004-10-01T07:23:57+09:00
Subject: RPN Fun

Perl's Quiz of the Week this time around was to make an RPN calculator. 
  If you're one of those people who has fond memories of HP's RPN 
calculators, you might want to play with this code a little.  Just 
thought I would share.

It understand postfix notation.  You can do:

3 <enter>
5 <enter>
+ <enter>

or

3 <space> 5 <space> + <enter>

It'll break it down term by term.  It understands Ruby numbers like -3 
and 0b101_010 and even allows commas in them.  It supports most of 
Ruby's math routines and even better, lets you define your own with:

def <space> OPERATOR <space> PROC_CODE <enter>

Those must be on their own line.  Example:

def avg { |left, right| (left + right) / 2.0 }

It'll know that's a binary operator because it takes two args.  
Anything else is considered unary.

If anyone has any use for this, just tell me and I'll throw it on the 
RAA.  I was just having a little flashback fun.

Enjoy.

James Edward Gray II

  #!/usr/bin/env ruby

# class for generating RPN Calculator objects
class RPNCalc
	attr_accessor :mode		# defines methods mode() and mode = ...
	
	# handles setup after constructor
	def initialize( mode = "dec", stack = [ ] )
		@mode = mode
		@stack = stack
		
		@ops = { }
	end
	
	### Stack manipulation methods ###
	
	# primary input method, adds something to stack if it's numerical
	def push( number )
		if number.kind_of? Numeric	# don't touch non-numbers
			# the following if converts floats to ints, when it doesn't matter
			if number.kind_of?(Float) and number == number.to_i
				@stack.unshift( number.to_i )
			else
				@stack.unshift( number )
			end
			return top	# return top value, what we just added
		else
			return nil
		end
	end
	# pop from stack
	def drop( ) return unary { nil } end
	# swap top two elements from stack
	def swap( )
		return binary do |l, r|
			push( r )
			l
		end
	end
	# empty stack
	def clear( ) return @stack = [ ] end
	def dup( )
		return unary do |num|
			push( num )
			num
		end
	end
	# arbitrary stack position swap (up)
	def roll( )
		if @stack.size < top
			raise "Insufficient elements on stack for operation."
		end

		return unary { |num| @stack.delete_at(num) }
	end
	# arbitrary stack position swap (down)
	def rolld( )
		if @stack.size < top
			raise "Insufficient elements on stack for operation."
		end

		return binary do |num, n|
			@stack.insert(n, num)
			nil
		end
	end
	
	### Basis math methods ###
	
	def add( ) return binary { |l, r| l + r } end
	def sub( ) return binary { |l, r| l - r } end
	def mul( ) return binary { |l, r| l * r } end
	def mod( ) return binary { |l, r| l % r } end
	def pow( ) return binary { |l, r| l ** r } end
	def div( )
		return binary do |l, r|
			# defeat Ruby's integer division
			if l.integer? and r.integer? and l % r != 0
				l / r.to_f
			else
				l / r
			end
		end
	end

	### To int methods ###
	
	def floor( ) return unary { |num| num.floor } end
	def ceil( ) return unary { |num| num.ceil } end
	def round( ) return unary { |num| num.round } end
	
	### Higher math methods ###
	
	def abs( ) return unary { |num| num.abs } end
	def sqrt( ) return unary { |num| Math.sqrt( num ) } end
	def exp( ) return unary { |num| Math.exp( num ) } end
	def log( ) return unary { |num| Math.log( num ) } end
	def log10( ) return unary { |num| Math.log10( num ) } end
	def sin( ) return unary { |num| Math.sin( num ) } end
	def cos( ) return unary { |num| Math.cos( num ) } end
	def tan( ) return unary { |num| Math.tan( num ) } end
	def sinh( ) return unary { |num| Math.sinh( num ) } end
	def cosh( ) return unary { |num| Math.cosh( num ) } end
	def tanh( ) return unary { |num| Math.tanh( num ) } end
	def asin( ) return unary { |num| Math.asin( num ) } end
	def acos( ) return unary { |num| Math.acos( num ) } end
	def atan( ) return unary { |num| Math.atan( num ) } end
	def asinh( ) return unary { |num| Math.asinh( num ) } end
	def acosh( ) return unary { |num| Math.acosh( num ) } end
	def atanh( ) return unary { |num| Math.atanh( num ) } end
	def atan2( ) return binary { |l, r| Math.atan2( l, r ) } end

	### Bitewise manipulation methods ###

	# Warning:  These methods convert their operands to ints before 
operation
	def bit_and( ) return binary { |l, r| l.to_i & r.to_i } end
	def bit_or( ) return binary { |l, r| l.to_i | r.to_i } end
	def bit_xor( ) return binary { |l, r| l.to_i ^ r.to_i } end
	def bit_neg( ) return unary { |num| ~num.to_i } end
	
	### Operator definition methods ###
	
	# adds Ruby code as new operator
	def define_op( op, &code )
		@ops[op] = code
	end
	
	### Input/Output methods ###
	
	# parses and executes expressions in postfix notation
	# also understands "def OP RUBY_PROC_CODE" on it's own line
	def calc( postfix_exp )
		if postfix_exp =~ /^\s*def\s+(\S+)\s+(\{.+\})\s*$/	# define new op
			define_op( $1.downcase, &eval( "proc #{$2}" ) )
		else	# ... or process terms
			terms = postfix_exp.downcase.split(" ")
			terms.each do |t|
				if @ops.include? t	# use custom op definition
					if @ops[t].arity == 2	# choose handler by proc args
						binary &@ops[t]
					else
						unary &@ops[t]
					end
					next
				end
				
				case t	# ... or hardcoded definition
					when "+" then add
					when "-" then sub
					when "*" then mul
					when "%" then mod
					when "**" then pow
					when "/" then div
	
					when "&" then bit_and
					when "|" then bit_or
					when "^" then bit_xor
					when "~" then bit_neg
	
					when /^-?(?:\d[,_\d]*|0[,_0-7]+|0x[,_0-9a-f]+|0b[,_01]+)$/,
						 /^-?\d[,_\d]*\.\d[,_\d]*(?:e-?[,_\d]+)?$/
						push( eval( t.tr(",", "") ) )
	
					when "drop", "swap", "clear", "dup", "roll", "rolld",
						 "floor", "ceil", "round",
						 "abs", "sqrt",
						 "exp", "log", "log10",
						 "sin", "cos", "tan", "sinh", "cosh", "tanh",
						 "asin", "acos", "atan", "asinh", "acosh", "atanh",
						 "atan2"
						send( t.to_sym )
	
					when "bin", "dec", "hex", "oct"
						@mode = t
	
					else
						raise "Invalid term: #{t}."
				end
			end
		end
		return top
	end
	# getter for top of stack
	def top( ) return @stack[0] end
	# primary output method, display stack with optional limit
	def to_s( limit = @stack.size )
		if @stack.size == 0
			return "Empty Stack\n"
		else
			case @mode
				when "bin"
					return (0...limit).to_a.reverse.inject("") do |str, i|
						str + "#{i}: #{'%b' % @stack[i]}\n"
					end
				when "dec"
					return (0...limit).to_a.reverse.inject("") do |str, i|
						str + "#{i}: #{@stack[i]}\n"
					end
				when "hex"
					return (0...limit).to_a.reverse.inject("") do |str, i|
						str + "#{i}: #{'%x' % @stack[i]}\n"
					end
				when "oct"
					return (0...limit).to_a.reverse.inject("") do |str, i|
						str + "#{i}: #{'%o' % @stack[i]}\n"
					end
			end
		end
	end
	
	private
	
	### Operator processing methods ###
	
	def unary( &op )
		if @stack.size < 1
			raise "Insufficient elements on stack for operation."
		end
		
		return push( op.call( @stack.shift ) )
	end
	def binary( &op )
		if @stack.size < 2
			raise "Insufficient elements on stack for operation."
		end
		
		right, left = @stack.slice!(0, 2)
		return push( op.call( left, right ) )
	end
end

# basic stand-alone interface, just process lines and show the stack...
if __FILE__ == $0
	rpn = RPNCalc.new

	print "\n" + rpn.to_s + "\n"
	print ">  " if STDIN.tty?
	while line = ARGF.gets
		line.chomp!
		if STDIN.tty? and line =~ /^q(?:uit)?|exit$/i
			break
		else
			begin
				rpn.calc line
			rescue
				puts "Error: " + $!
			end
			print "\n" + rpn.to_s + "\n"
			print ">  " if STDIN.tty?
		end
	end
end

__END__