GRASS (programming language): Difference between revisions

Revision as of 18:45, 29 September 2017

Revision as of 19:05, 29 September 2017

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Programs in Zgrass were referred to as "macros", and stored as strings. Both of these oddities were deliberate, as Zgrass allowed any string to become a program. For instance, <code>MYBOX="BOX 0,0,100,100,2"</code> defines a string (no need for a $ as in BASIC) containing a snippet of Zgrass code. Simply typing <code>MYBOX</code> from that point on would run the command(s) inside. This feature can be used in place of the more traditional <code>[[GOSUB]]</code> command from BASIC, but has the added advantage of having a well defined name as opposed to an opaque line number. In addition the command remains a string, and can be manipulated at runtime with standard string operations.

Most BASIC [[interpreter (computer software)|interpreters]] of the era converted the input text into a "''[Lexical analysis|tokenized"]'' version in which each of the commands was replaced by a single number (typically one [[byte]] long). This made the program run faster because it didn't have to continually decode the commands from the strings every time. Zgrass's use of string-based macros made this difficult, so they didn't bother with tokenization. Instead they included a [[compiler]] which could be used on any particular macro, speeding it up many times. Programs would often consist of a mix of compiled and uncompiled macros.

Line numbers were optional in Zgrass, and typically only appeared on lines that were the target of a <code>GOTO</code>. Most BASIC interpreters required line numbers for every line of code, but this was due to their use in the "line editor"&ndash;if you needed to edit ''that'' line, the only way to refer to it was by number. Zgrass used a more advanced full-screen editor that eliminated this need.<ref group=notes>As was the case for [[True BASIC]] and most dialects after that time.</ref> Zgrass allowed any string to act as a "line number", <code>GOTO 10</code> and <code>GOTO MARKER</code> were both valid. Zgrass also included nameless branches, using the <code>SKIP</code> instruction, which would move forward or back a given number of lines.