Editing BASIC09 (section)

===Editing===
Line numbers were used in most BASIC dialects primarily as a way to support the editor. Users would edit particular lines of code by typing a number, with the text following either adding to or replacing the lines already in memory. As every line of code had a number, this also made them suitable for indicating the target of a <code>GOTO</code> or <code>GOSUB</code>, compared to other languages like [[FORTRAN]] where a separate "line label" was used for this purpose.

BASIC09 did not normally use line numbers, so its editor had to be modified to allow the user to edit lines without referring to them by number. However, BASIC09 did not assume any sort of full-screen capability, so using [[cursor keys]] was not an option. Instead, the system had a separate editor prompt and allowed the user to move about using the {{tt|+}} and {{tt|-}} keys, moving forward or backward one line at a time. To insert a new line of code without a line number, the user left a blank at the start of the statement.{{sfn|Manual|1984|p=2.3}}

Note that the language is [[case sensitive]] for user-provided values like procedure and variable names, but not for keywords. Keywords typed into the editor in lower case will be shown in upper case when the program is <code>LIST</code>ed.{{sfn|Manual|1984|p=2.5}} BASIC09 allowed multiple statements on a single line of code, but used the {{tt|\}} as a separator instead of the {{tt|:}} used in most dialects.{{sfn|Manual|1984|p=9.1}}{{efn|The colon was being used for the data type in the <code>DIM</code> statements.}} This is because it used the colon in the <code>:=</code> assignment operator, which was in addition to the normal <code>=</code>. <code>:=</code> was identical in effect to <code>=</code>, but made the difference between assignments and comparisons more obvious.{{sfn|Manual|1984|p=9.2}}