The BBC and Master Computer Public Domain Library
9B52 Check for '=', get expression result & check end of statement
Submitted by Steve Fewell
Description:
If called from 9B46, then copy BASIC Text Pointer A to BASIC Text Pointer B.
Increment BASIC Text pointer B offset, load the next non-space character pointed to
by BASIC Text pointer B. If the next character is not '=' then issue a Mistake error, as
the current statement is not correct BASIC.
Otherwise, all is well, so jump to &9B8E, which does the following:
Evaluate the expression after the '='.
Then set A = X (this is the next non-space charater after the expression).
Next, load Y wth the BASIC Text pointer B offset (so that routine &9BB0 can update
the BASIC Text pointer A position correctly).
Finally, jump to &9BB0 to check for the end of statement (issuing a Syntax error if the
statement is not terminated correctly), and update BASIC Text Pointer A to point to the location
after the end of the current statement, and exit.
Disassembly for the Check for '=', get expression result & check end of statement routine
| 9B46 | 165 011 | A5 0B | LDA &0B | |
| 9B48 | 133 025 | 85 19 | STA &19 | |
| 9B4A | 165 012 | A5 0C | LDA &0C | |
| 9B4C | 133 026 | 85 1A | STA &1A | |
| 9B4E | 165 010 | A5 0A | LDA &0A | |
| 9B50 | 133 027 | 85 1B | STA &1B | |
| 9B52 | 164 027 | A4 1B | LDY &1B | |
| 9B54 | 230 027 | E6 1B | INC &1B | |
| 9B56 | 177 025 | B1 19 | LDA (&19),Y | |
| 9B58 | 201 032 | C9 20 | CMP#&20 | |
| 9B5A | 240 246 | F0 F6 | BEQ -10 --> &9B52 | |
| 9B5C | = | 201 061 | C9 3D | CMP#&3D |
| 9B5E | . | 240 046 | F0 2E | BEQ 46 --> &9B8E Evaluate expression & check end of statement |
| 9B60 | ... Mistake error |
Evaluate expression and check for end of statement
| 9B8E | ; | 032 059 157 | 20 3B 9D | JSR &9D3B Evaluate expression |
| 9B91 | 138 | 8A | TXA | |
| 9B92 | 164 027 | A4 1B | LDY &1B | |
| 9B94 | 128 026 | 80 1A | BRA 26 --> &9BB0 Check for end of Statement |
