GRASS (programming language): Difference between revisions

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===ZGRASS and UV-1===

In 1977, DeFanti was introduced to Jeff Frederiksen, a chip designer working at [[Dave Nutting Associates]]. Nutting had been contracted by Midway, the videogame division of Bally, to create a standardized [[videoVideo display unitcontroller|graphics driver chip]]. They intended to use it in most of their future arcade games, as well as a [[video game console]] they were working on which would later turn into the [[Astrocade]]. Midway was quite interested in seeing the GRASS language running on their system, and contracted DeFanti to port it to the platform. A number of people at the Habitat, as well as some from Nutting, worked on the project, which they referred to as the '''Z Box'''. GRASS3 running on it became '''ZGRASS'''.{{sfn|DeFanti|1980}}

The Z-Box was a [[raster graphics]] machine, unlike the original GRASS systems, so while most of the GRASS3 style was maintained in ZGRASS, it added a number of commands dedicated to raster images. This included an extensive set of [[bit blit|bit block transfer]] commands in order to simulate [[sprite (computer science)|sprite]]s, something the hardware didn't include.{{sfn|DeFanti|1980}} The work would never be released by Midway, but the Circle would produce machines based on it as the [[Datamax UV-1]].

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== Description ==

:''This description is based on the original Bally manuals as well as the ACM description.''{{sfn|DeFanti|Fenton|Donato|1978}}

Zgrass was based on a standard set of BASIC commands and used most of its syntax. Where Zgrass differed from BASIC was that all commands were in fact [[function (programming)|function]]s and returned values, similar to the [[C (programming language)|C programming language]]. If there was no obvious return value it was expected that a function would return 1 if it succeeded, and 0 if it failed. For instance, the command <code>PRINT PRINT 10</code> would be illegal in BASIC, but in Zgrass this would print <code>10 1</code>, the 1 being the value returned by second <code>PRINT</code>, meaning "I successfully output the string '10'".

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Zgrass also included a series of commands that "covered" CP/M, which allowed the disk to be accessed without exiting to the command prompt. You could easily save out macros to named files, and load them in the same way, allowing you to construct programs by loading up various macros from the disk into one large program. The commands also automatically made a backup copy of every save. Similar features were supported for [[Compact Cassette (data)|Compact Cassette]] storage, but oddly the syntax was not parallel: disk commands were D-something, like {{code|DPUT}}, but tape commands were not T-something, like {{code|TPUT}}, but rather something-TAPE, like {{code|PUTTAPE}}.

With programs constructed from randomlyarbitrarily selected modules, Zgrass needed to have better control over its variables than BASIC. In BASIC all variables are "global", so if two subroutines both use the variable {{code|I}}, which is very commonly used as a loop index variable, then they could set each other's values which leads to hard-to-debug problems. Under Zgrass a programmer loading up two modules could easily find that both used {{code|I}} as a loop counter, which could cause problems. To address this issue, Zgrass considered variables named with [[lowercase]] letters to be local only to that macro, so {{code|I}} and {{code|i}} were different variables, global and local respectively. Oddly, the examples provided with the language do not make widespread use of this feature, potentially confusing new programmers who might not be aware the feature exists.

==Example==