## 39 Package alt-display ¶

### 39.1 Introduction to alt-display ¶

The alt-display package provides a means to change the way that Maxima displays its output. The *alt-display1d* and *alt-display2d* Lisp hooks were introduced to Maxima in 2002, but were not easily accessible from the Maxima REPL until the introduction of this package.

The package provides a general purpose function to define alternative display functions, and a separate function to set the display function. The package also provides customized display functions to produce output in TeX, Texinfo, XML and all three output formats within Texinfo.

Here is a sample session:

    (%i1) load("alt-display.mac")$
    (%i2) set_alt_display(2,tex_display)$

    (%i3) x/(x^2+y^2) = 1;
    \mbox{\tt\red({\it \%o_3}) \black}$${{x}\over{y^2+x^2}}=1$$

    (%i4) set_alt_display(2,mathml_display)$

    (%i5) x/(x^2+y^2) = 1;
    <math xmlns="http://www.w3.org/1998/Math/MathML"> <mi>mlabel</mi>
    <mfenced separators=""><msub><mi>%o</mi> <mn>5</mn></msub>
    <mo>,</mo><mfrac><mrow><mi>x</mi> </mrow> <mrow><msup><mrow>
    <mi>y</mi> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup><mrow>
    <mi>x</mi> </mrow> <mn>2</mn> </msup> </mrow></mfrac> <mo>=</mo>
    <mn>1</mn> </mfenced> </math>

    (%i6) set_alt_display(2,multi_display_for_texinfo)$

    (%i7) x/(x^2+y^2) = 1;

    @iftex
    @tex
    \mbox{\tt\red({\it \%o_7}) \black}$${{x}\over{y^2+x^2}}=1$$
    @end tex
    @end iftex
    @ifhtml
    @html

    <math xmlns="http://www.w3.org/1998/Math/MathML"> <mi>mlabel</mi>
    <mfenced separators=""><msub><mi>%o</mi> <mn>7</mn></msub>
    <mo>,</mo><mfrac><mrow><mi>x</mi> </mrow> <mrow><msup><mrow>
    <mi>y</mi> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup><mrow>
    <mi>x</mi> </mrow> <mn>2</mn> </msup> </mrow></mfrac> <mo>=</mo>
    <mn>1</mn> </mfenced> </math>
    @end html
    @end ifhtml
    @ifinfo
    @example
    (%o7) x/(y^2+x^2) = 1
    @end example
    @end ifinfo

If the alternative display function causes an error, the error is trapped and the display function is reset to the default display. In the following example, the `error` function is set to display the output. This throws an error, which is handled by resetting the 2d-display to the default.

    (%i8) set_alt_display(2,?error)$

    (%i9) x;

    Error in *alt-display2d*.
    Message: Condition designator ((MLABEL) $%O9 $X) is not of type
            (OR SYMBOL STRING FUNCTION).
    *alt-display2d* reset to nil.
     -- an error. To debug this try: debugmode(true);

    (%i10) x;
    (%o10)                                 x

### 39.2 Functions and Variables for alt-display ¶

Function: alt_display_output_type (form) ¶

  Determine the type of output to be printed. Form must be a lisp form suitable for printing via Maxima’s built-in `displa` function. At present, this function returns one of three values: text, label or unknown.

  An example where `alt_display_output_type` is used. In `my_display`, a text form is printed between a pair of tags `TEXT;>>` and `<<TEXT;` while a label form is printed between a pair tags `OUT;>>` and `<<OUT;` in addition to the usual output label.

  The function `set_prompt` also ensures that input labels are printed between matching `PROMPT;>>` and `<<PROMPT;` tags.

  Thanks to Eric Stemmler.

      (%i1) (load("mactex-utilities"), load("alt-display.mac")) $

      (%i2) define_alt_display(my_display(form),
      block([type,txttmplt,labtmplt],
      txttmplt:"~%TEXT;>>~%~a~%<<TEXT;~%",
      labtmplt:"~%OUT;>>~%(~a) ~a~a~a~%<<OUT;~%",
      type:alt_display_output_type(form),
      if type='text then
         printf(true,txttmplt,first(form))
      else if type='label then
           printf(true,labtmplt,first(form),"$$",tex1(second(form)),"$$")
      else
           block([alt_display1d:false, alt_display2d:false], displa(form)))) $

      (%i3) (set_prompt('prefix, "PROMPT;>>",'suffix, "<<PROMPT;"),
            set_alt_display(1,my_display)) $

      PROMPT;>>(%i4) <<PROMPT;integrate(x^n,x);
      PROMPT;>>
      TEXT;>>
      Is n equal to -1?
      <<TEXT;
      <<PROMPT;
      n;

      OUT;>>
      (%o4) $$\frac{x^{n+1}}{n+1}$$
      <<OUT;
      PROMPT;>>(%i5) <<PROMPT;

  Categories: Package alt-display ·

Function: define_alt_display (function(input), expr) ¶

  This function is similar to `define`: it evaluates its arguments and expands into a function definition. The function is a function of a single input input. For convenience, a substitution is applied to expr after evaluation, to provide easy access to Lisp variable names.

  Set a time-stamp on each prompt:

      (%i1) load("alt-display.mac")$

      (%i2) display2d: false$

      (%i3) define_alt_display(time_stamp(x),
                      block([alt_display1d:false,alt_display2d:false],
                            prompt_prefix:printf(false,"~a~%",timedate()),
                            displa(x)));

      (%o3) time_stamp(x):=block(
                       [\*alt\-display1d\*:false,
                        \*alt\-display2d\*:false],
                       \*prompt\-prefix\*
                        :printf(false,"~a~%",timedate()),displa(x))
      (%i4) set_alt_display(1,time_stamp);

      (%o4) done
      2017-11-27 16:15:58-06:00
      (%i5)

  The input line `%i3` defines `time_stamp` using `define_alt_display`. The output line `%o3` shows that the Maxima variable names `alt_display1d`, `alt_display2d` and `prompt_prefix` have been replaced by their Lisp translations, as has `displa` been replaced by `?displa` (the display function).

  The display variables `alt_display1d` and `alt_display2d` are both bound to `false` in the body of `time_stamp` to prevent an infinite recursion in `displa`.

  Categories: Package alt-display ·

Function: info_display (form) ¶

  This is an alias for the default 1-d display function. It may be used as an alternative 1-d or 2-d display function.

      (%i1) load("alt-display.mac")$

      (%i2) set_alt_display(2,info_display);

      (%o2) done
      (%i3) x/y;

      (%o3) x/y

  Categories: Package alt-display ·

Function: mathml_display (form) ¶

  Produces MathML output.

      (%i1) load("alt-display.mac")$

      (%i2) set_alt_display(2,mathml_display);
      <math xmlns="http://www.w3.org/1998/Math/MathML"> <mi>mlabel</mi>
       <mfenced separators=""><msub><mi>%o</mi> <mn>2</mn></msub>
       <mo>,</mo><mi>done</mi> </mfenced> </math>

  Categories: Package alt-display ·

Function: tex_display (form) ¶

  Produces TeX output.

      (%i2) set_alt_display(2,tex_display);
      \mbox{\tt\red({\it \%o_2}) \black}$$\mathbf{done}$$
      (%i3) x/(x^2+y^2);
      \mbox{\tt\red({\it \%o_3}) \black}$${{x}\over{y^2+x^2}}$$

  Categories: Package alt-display ·

Function: multi_display_for_texinfo (form) ¶

  Produces Texinfo output using all three display functions.

      (%i2) set_alt_display(2,multi_display_for_texinfo)$

      (%i3) x/(x^2+y^2);

      @iftex
      @tex
      \mbox{\tt\red({\it \%o_3}) \black}$${{x}\over{y^2+x^2}}$$
      @end tex
      @end iftex
      @ifhtml
      @html

         <math xmlns="http://www.w3.org/1998/Math/MathML"> <mi>mlabel</mi>
         <mfenced separators=""><msub><mi>%o</mi> <mn>3</mn></msub>
         <mo>,</mo><mfrac><mrow><mi>x</mi> </mrow> <mrow><msup><mrow>
         <mi>y</mi> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup><mrow>
         <mi>x</mi> </mrow> <mn>2</mn> </msup> </mrow></mfrac> </mfenced> </math>
      @end html
      @end ifhtml
      @ifinfo
      @example
      (%o3) x/(y^2+x^2)
      @end example
      @end ifinfo

  Categories: Package alt-display ·

Functions: reset_displays () ¶

  Resets the prompt prefix and suffix to the empty string, and sets both 1-d and 2-d display functions to the default.

  Categories: Package alt-display ·

Function: set_alt_display (num, display-function) ¶

  The input num is the display to set; it may be either 1 or 2. The second input display-function is the display function to use. The display function may be either a Maxima function or a `lambda` expression.

  Here is an example where the display function is a `lambda` expression; it just displays the result as TeX.

      (%i1) load("alt-display.mac")$

      (%i2) set_alt_display(2, lambda([form], tex(?caddr(form))))$

      (%i3) integrate(exp(-t^2),t,0,inf);
      $${{\sqrt{\pi}}\over{2}}$$

  A user-defined display function should take care that it prints its output. A display function that returns a string will appear to display nothing, nor cause any errors.

  Categories: Package alt-display ·

Function: set_prompt (fix, expr) ¶

  Set the prompt prefix or suffix to expr. The input fix must evaluate to one of `prefix`, `suffix`, `general`, `prolog` or `epilog`. The input expr must evaluate to either a string or `false`; if `false`, the fix is reset to the default value.

      (%i1) load("alt-display.mac")$
      (%i2) set_prompt('prefix,printf(false,"It is now: ~a~%",timedate()))$

      It is now: 2014-01-07 15:23:23-05:00
      (%i3)

  The following example shows the effect of each option, except `prolog`. Note that the `epilog` prompt is printed as Maxima closes down. The `general` is printed between the end of input and the output, unless the input line ends in `$`.

  Here is an example to show where the prompt strings are placed.

      (%i1) load("alt-display.mac")$

      (%i2) set_prompt(prefix, "<<prefix>> ", suffix, "<<suffix>> ",
                       general, printf(false,"<<general>>~%"),
                       epilog, printf(false,"<<epilog>>~%"));

      (%o2)                                done
      <<prefix>> (%i3) <<suffix>> x/y;
      <<general>>
                                             x
      (%o3)                                  -
                                             y
      <<prefix>> (%i4) <<suffix>> quit();
      <<general>>
      <<epilog>>

  Here is an example that shows how to colorize the input and output when Maxima is running in a terminal or terminal emulator like Emacs8.

  Each prompt string starts with the ASCII escape character (27) followed by an open square bracket (91); each string ends with a lower-case m (109). The webpages https://misc.flogisoft.com/bash/tip_colors_and_formatting and https://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/x329.html provide information on how to use control strings to set the terminal colors.

  Categories: Package alt-display ·

#### Footnotes

##### (8)

Readers using the `info` reader in `Emacs` will see the actual prompt strings; other readers will see the colorized output