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Chapters:
  1: Introduction
  2: Simple example
  3: Invocation
  4: Finer Control
  5: X-Y Plots
  6: Contour Plots
  7: Image Plots
  8: Examples
  9: Gri Commands
  10: Programming
  11: Environment
  12: Emacs Mode
  13: History
  14: Installation
  15: Gri Bugs
  16: Test Suite
  17: Gri in Press
  18: Acknowledgments
  19: License

Indices:
  Concepts
  Commands
  Variables
 		index.html#Top NewCommands.html#AddingNewCommands Gri: creating a simple new command Gri: making a newcommand change its arguments index.html#Top Gri: making a newcommand change its arguments

10.11.4: Complicated example of a new command

The following example from the global `gri.cmd' file illustrates how to parse/check the commandline (see Local Synonyms), which is a good practice in any code you expect to re-use. The first `if' statement checks that the word `at' is in the right place (this would not have been checked by the syntax matcher, the word having followed a string). The presence of the keyword `cm' is checked for, and user units or cm units are used accordingly. Local variables are created (`new') and then destroyed (`delete') so that this new command cannot affect outside code. 


`draw label whiteunder "\string" at .xleft. .ybottom. [cm]'
Draw label for plot, located with lower-left corner
at indicated (x,y) position (specified in user
units or in cm on the page).  Whiteout is used
to clean up the area under the label.  BUGS:
Cannot handle angled text; doesn't check for
super/subscripts.
{
    if {rpn "\.word4." "at" !=}
      show "ERROR: 5th word must be `at', not `\.word4.'"
      show traceback
      quit
    end if 
    new .x. .y. .oldgray. .space.
    if {rpn \.words. 7 ==}
      .x. = {rpn \.word5. xusertocm}
      .y. = {rpn \.word6. yusertocm}
    else if {rpn \.words. 8 ==}
      if {rpn "\.word7." "cm" !=}
        show "ERROR: Require 8th word to be `cm'"
        show traceback
        quit
      end if
      .x. = \.word5.
      .y. = \.word6.
    else
      show "ERROR: Require 7 or 8 words, not \.words."
      show traceback
      quit
    end if
    # Coordinates now in cm.  Next, white out a box
    # under the text (and .space. centimetres
    # beyond text), then draw label.
    .space. = 0.1               # Space of 1mm
    .oldgray. = ..graylevel..
    set graylevel white
    draw box filled                          \
      {rpn .x. .space. -}                    \
      {rpn .y. .space. -}                    \
      {rpn .x. "\.word3." width + .space. +} \
      {rpn .y. "M" ascent + .space. + } cm
    set graylevel .oldgray.
    draw label "\.word3." at .x. .y. cm
    delete .x. .y. .oldgray. .space.
}

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