Editing GRASS (programming language) (section)

==Example==
{{sxhl|2=basic|1=<nowiki/>
 SINCURVE=[PROMPT "WHAT IS THE OFFSET?"
 INPUT OFFSET
 x=-160
 angle=0
 POINT OFFSET+x,SIN(angle)*80,3
 angle=angle+2
 IF (x=x+1)<159,SKIP -2]
}}
This text creates a new macro called <code>SINCURVE</code> that can be called simply by typing <code>SINCURVE</code> into the command prompt, or from other macros or programs. SINCURVE uses two local variables, <var>x</var> and <var>angle</var>, as well as a global variable, <var>OFFSET</var>.

The <code>PROMPT</code>/<code>INPUT</code> is a modification of the original BASIC <code>INPUT</code> which will not ask for the input if the user types it into the command line when calling the macro. In this case, typing <code>SINCURVE</code> will result in the prompt appearing and the program waiting for input, whereas typing <code>SINCURVE 30</code> will skip the prompt and OFFSET will automatically be assigned 30. This allows a single macro to be used both interactively and within a program as a function.

<code>POINT</code> is an example of one of the many graphics commands included in the Zgrass language. <code>POINT</code> requires an X and Y location, as well as a color. In this example, the user supplied <code>OFFSET</code> moves the x position of the curve on the screen, while the Y position is supplied by the [[trigonometry|trig function]], suitably enlarged for display (in this case, 80 times). The color is supplied in the last input, and in this case is 3. The UV-1 used color registers, so 3 did not imply a particular color, but a color selected from the current palette.

The <code>IF</code> is likewise notable. It places an increment, <code>(x=x+1)</code>, in front of the test, a feature not normally available in BASIC. In this case the IF is told to call <code>SKIP -2</code> if true, which will move back two lines and can be used in place of a <code>GOTO</code>, as there is no line number target.