The BBC and Master Computer Public Domain Library

BA17 UNTIL

Submitted by Steve Fewell

Description:

Call routine &9D2F to set BASIC text Pointer B to the BASIC text pointer A value and get the result of the expression
pointed to by BASIC text pointer B.

Call routine &9B91 to check for the end of the Statement - if the end of statement (either a ':', '<cr>' or 'ELSE'
character) is not found after the expression then issue 'Syntax error', as the UNTIL statement does not finish correctly.

Call routine &96BC to check the result type of the expression (location &27), and convert the expression result
value to an Integer if it is a Floating-Point value, or issue 'Type mismatch' error if it is a String value.
The IWA now contains the value of the result of the expression.

Load X with the current REPEAT level (from location &24).
If X is zero, then no outstanding REPEAT statements are active, so issue 'No REPEAT' error.

Check the IWA result value - if the IWA contains zero, then the result of the UNTIL expression is false, so [&BA33]
load Y with the LSB of the REPEAT start address from the REPEAT start address stack (&04FF + X (current REPEAT
level)) and load A with the MSB of the REPEAT start address from the REPEAT start address stack (&0513 + X (current
REPEAT level)), and jump to &B732 to set the BASIC text pointer A to the REPEAT start address value (in Y and A) and
jump to &900B to continue executing the program from the REPEAT start address.

Otherwise, the UNTIL expression is true, and we have finished the REPEAT...UNTIL loop, so decrement the current
REPEAT level - so that it is now set to the level before the REPEAT loop began, and jump to &9005 to continue
executing the program, starting with the next program statement after the UNTIL statement.

Disassembly for the UNTIL routine