Charles C wrote:

> All I can say is "why not." Calculators cost money but you can make one for
> free.  Actually I have my old HP48 but wanted to do this anyway.
> 
> Where I got stuck before (this is an old project which I recently came back
> to) was that I needed to be able to have a whole arbitrary expression as a
> string that I could display as well as evaluating it to a float that I
> could plot.  val() of course can convert a string literal to a float, but
> val("2+2") returns the number 2.
> 
> It seemed somewhat cumbersome to do so, but I finally gave in and outputted
> strings to a file, to be read back in as a macro holding an expression.
> Here's that macro to create the temp file:
> 
> #macro Make_Temporary_Expression_Macro_File(Eq)
>         #fopen  Calculator_Temp_Expression_File
> "Temporary_Expression_Macro_File.tmp"  write
>         #write (Calculator_Temp_Expression_File, "/* This is a temporary
> file generated and used by calculator.pov and can be deleted without harm.
> */n")
>         #write (Calculator_Temp_Expression_File, "#macro Evaluate_Eq_For_X
> (X)  n")
>         #write (Calculator_Temp_Expression_File, "      #declare Eq_Y = " )
>         #write (Calculator_Temp_Expression_File, Eq ) //the function
>         #write (Calculator_Temp_Expression_File, "; n#end n" )
>         #fclose Calculator_Temp_Expression_File
> #end // end  Make_Temporary_Expression_Macro_File
> 
> Any better ideas?  The little temp file gets written over once for each
> function and once for each expression.

I did something like this for an AmigaBasic program about a dozen years 
ago.  I had the program use RPN for the expressions, because they're 
much simpler to parse.

Regards,
John

Post a reply to this message