[Maxima-bugs] [maxima:bugs] #4567 gnuplot gives obscure Lisp error when gnuplot_command is not a string

[Raymond T. <rt...@us...>]

- **status**: open --> closed
- **assigned_to**: Raymond Toy
- **Comment**:

Fixed by commit [c2af73] which forces `$gnuplot_command` t o be a string.



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**[bugs:#4567] gnuplot gives obscure Lisp error when gnuplot_command is not a string**

**Status:** closed
**Group:** None
**Labels:** gnuplot 
**Created:** Sat Jun 14, 2025 11:35 AM UTC by Wolfgang Dautermann
**Last Updated:** Tue Jun 17, 2025 02:00 PM UTC
**Owner:** Raymond Toy


Dear all,
When one outputs a variable, there is no 'type' printed - is there a (native) function to query the type? Yes, e.g `numberp()`, for numbers, but in general?

E.g. I query `gnuplot_command`,  then I set it to the same value:

~~~
(%i1) gnuplot_command;
(%o1)                               gnuplot
(%i2) gnuplot_command:gnuplot;
(%o2)                               gnuplot
(%i3) plot2d(x,[x,1,2]);

Maxima encountered a Lisp error:

 The value
   $GNUPLOT
 is not of type
   (OR STRING PATHNAME SYNONYM-STREAM FILE-STREAM)
 when binding PATHNAME

Automatically continuing.
To enable the Lisp debugger set *debugger-hook* to nil.
~~~
That did not work, the variable is now of type symbol, not longer a string. But if I output the variable, I get not idea, if it is a string or symbol. It must be set enclosed in quotation marks, then it works.
~~~
(%i4) gnuplot_command:"gnuplot";
(%o4)                               gnuplot
(%i5) plot2d(x,[x,1,2]); /* works ok */
~~~

Is there any (native) function or output (`typeof()` or something else?) where one can get an idea, whats wrong?
Because the OUTPUT of `gnuplot_command` is the same in both cases. (Maybe it should be `"gnuplot"` in the string case)?

I found `:lisp (type-of $a)` but there is no Maxima equivalent?
Best regards, Wolfgang


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