From: Jason Roelofs <jameskilton@...>
Date: 2007-06-05T04:45:42+09:00
Subject: Re: Help needed: Dynamically create a Proc from a String and evaluate it

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Can we see the code of your eval_formula?

Jason

On 6/4/07, Axel Etzold <AEtzold@gmx.de> wrote:
>
> Dear all,
>
> I need help in dynamically creating a Proc from  a String like, say,
>
>     a='f(x)=c*exp(x/k)',
>
> (I need to do this many times for many different formulas)
> which I want to use Ruby to calculate as a function of x, given
> constants c,k, i.e.,
> In this example, I want the following lines to produce,
>
> b=a.generate_formula  => "def f(x)\n\n return Proc.new{|c,x,k|
> c*exp(x/k) }\n end \n"
> c=a.eval_formula({'c',5.0,'k',2.0,'x',1.0}) => 5*exp(0.5)
>
> The first line is o.k., and I manage to change the string b
> to
>
> d="f(1.0).call(5.0,2.0)",
>
> but I can't eval it using
>
> eval(b) # (should make the function available as a Proc method)
> eval(d) # (should output the value at x=1.0)
>
> because the first variable,x ,  doesn't get its value assigned:
>
> t00.rb:102:in `eval_formula': (eval):6:in `/': nil can't be coerced into
> Float (TypeError)
>         from (eval):6:in `Ie'
>         from (eval):1:in `call'
>         from (eval):1:in `eval_formula'
>         from t00.rb:64:in `eval'
>         from t00.rb:102:in `eval_formula'
>         from t00.rb:64:in `each'
>         from t00.rb:64:in `eval_formula'
>         from t00.rb:131
>
> Is there a better way to do this ?
>
> Thank you!
>
> Best regards,
>
> Axel
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