From: Axel Etzold <AEtzold@...>
Date: 2007-06-05T05:44:46+09:00
Subject: Re: Help needed: Dynamically create a Proc from a String and evaluate it

Dear Brian,

thank you for responding.
However, I still haven't solved my problem.
So, following one of your suggestions, I get:

p 'function-text'
p f  => "eval('proc{|c,x,k| c*Math.exp(x/k) }')"
g=eval(f)=> #<Proc:0x00002b56c768ef68@(eval):1>

p g(1.0).call(2,5)  => undefined function or variable 'g'

I can't get to use the proc I just created.. Why not ?

Thank you, 
Axel 



-------- Original-Nachricht --------
Datum: Tue, 5 Jun 2007 04:55:57 +0900
Von: Brian Candler <B.Candler@pobox.com>
An: ruby-talk@ruby-lang.org
Betreff: 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.

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