From: Brian Candler <B.Candler@...>
Date: 2007-06-05T04:55:57+09:00
Subject: Re: Help needed: Dynamically create a Proc from a String and evaluate it

On Tue, Jun 05, 2007 at 04:18:58AM +0900, Axel Etzold wrote:
> I need help in dynamically creating a Proc from  a String like, say,
> 
>     a='f(x)=c*exp(x/k)',

If you're passing in c and k each time, then

b = eval("proc{|c,x,k| c*Math.exp(x/k) }")
puts b.call(5.0, 2.0, 1.0)

This means you only call eval once, to create the proc object, then you can
call it as many times as you like.

If c and k really are constants then you can substitute them in to the proc
definition:

c = 5
k = 2
a = eval("proc { |x| #{c}*Math.exp(x/#{k}) }")
puts a.call(3)

or you can use the closure property to bind the local variables directly:

c = 5
k = 2
a = eval("proc { |x| c*Math.exp(x/k) }")
puts a.call(3)

Brian.