Editing BASIC09 (section)

==Significant features==
* reasonably structured control flow provisions (e.g., line numbers were mainly needed for computed <code>[[GOTO]]</code>, as BASIC09 did not have a switch/case statement, or computed <code>[[GOSUB]]</code>)
* structure declaration (rare in any BASIC variant then; more common in later BASIC implementations)
* intrinsic integer and [[Boolean data type]]s
* more than two significant characters in variable names (some BASICs of the time allowed only one, many [[Microsoft BASIC]] variants allowed only two)
* procedures with local variables (indeed, ''all'' variables in BASIC09 are local to procedures) and parameter passing by reference
* a reasonable [[debug]]ger (its only significant drawback was that one could not examine the contents of fields in structures)
* a way to interface to [[machine language]] code, which could be passed parameters using the BASIC09 calling sequence
* automatic [[prettyprint]]ing of source, which enforced a standard layout and avoided the ghastly mess that was the usual appearance of a program of any size in the interpreted BASICs of the time. Programmers normally would cram as many lines together as possible to avoid line number memory overhead—not a problem in BASIC09<ref>[https://archive.org/stream/68micro-vol-09-num-04/V09N04_Apr1987#page/n15/mode/1up Basically OS-9], By Ron Voigts, 68 Micro Journal, Volume 09 Number 04, April 1984, Page 14, ''One of its strong features is its handling of formatted output. Other languages vary in how well they can handle the formatted output. But BASIC09 can do a very nice job of putting your lines into a form that you want''</ref>