From: "Luca (Email)" <luca.pagano@...>
Date: 2011-12-29T15:50:05+09:00
Subject: I: calculator program help



-----Messaggio originale-----
Da: Sylvester Keil [mailto:sylvester.keil@gmail.com] 
Inviato: marted́ 15 novembre 2011 11:05
A: ruby-talk ML
Oggetto: Re: calculator program help


On Nov 14, 2011, at 10:23 PM, Trevor Daniels wrote:

> I'm trying to make a simple RPN calculator that reads in regular 
> expressions from a file and evaluates them to execute code. Currently 
> I have these regular expressions stored in an array of class objects 
> that have 2 data objects (1. The regex itself and 2. The block of code 
> that should be executed when a match is found). An example of one of 
> the read in regex's is below:
> 
> [0-9]+
> lambda {|input| $myStack.push(input)}
> 
> Now, I get input from the user and compare that string to all the 
> regular expressions in my array. When a match is found, the code is 
> evaluated. So far it is working by entering in input one by one. Code 
> and an example are below.
> 
> while input = gets
>  for i in 0..$regexArray.length-1
>    if ( input =~ Regexp.new($regexArray[i].regex) )
>      eval($regexArray[i].code).call(input)
>    end
>  end
> end
> 
> Example:
> 5
> 4
> +
> print
> 
> will give "9" as it should. However, I want to make it so I can enter 
> input in one line like:
> 5 4 + print
> 
> I've tried matching the input string with the regex with: myMatch =
> regex.match(input)
> but when I enter a string such as "123 456" only the last part ("456") 
> is matched when I need to first match the ("123"). Any help would be 
> appreciated.

If your valid expressions contain no whitespace, you can split your input
into individual tokens with split(/\s+/). As a minimal example, this works
fine:


q = []
a = {
	/\d+/ => ->(input) { q << input.to_i },
	/\+|-/ => ->(op) { q.push(q.pop(2).reverse.reduce(op)) },
	/print/ => ->(match) { puts q.pop }
}

DATA.each_line do |input|
  input.split(/\s+/).each do |token|
    code = a[a.keys.detect { |k| token =~ k }]
    code.call(token) unless code.nil?
  end
end

__END__
5 4 + print
5 4 - print

Returns 9 and -1.

If you need to parse more complex input on each line, you should use
StringScanner available in the standard library (require 'strscan').



 
 
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