| C000
to C22B |
All this is data for the interpreter.
The interpreter looks in this area for a match for the
first letter of the word it is looking at. It then jumps
in the table to an area containing all the words
beginning with that first letter, and looks at the second
letter. It thus performs a tree search of the BASIC words
stored in this area. |
| C22C
to C278 |
A subroutine, the Function Interpreter.
This area evaluates the value of any arbitrarily complex
function pointed to by (5),Y, finds its value, then
stores the results on the workspace stack (see C3C8). |
| C279
to C2AC |
Looks up the "meaning" of
commands. If there is no match in the tree table at C000
it hands over to those kept at F000, if not there then
D000, if not there then A000, if not there then error.
The tree search is very quick and it seems that this is
the original Acorn interpreter. The later additions at
F000 and elsewhere are total linear searches and slower. |
| C2AD |
Executes the command NEW. This is
available to you, but exits back to direct mode. Enter
routine at C2B2. |
| C2B2
to C31A |
Execution of the <BREAK> key comes
to here from about FF94. It puts 0D FF into 2900,2901,
sets @=8, then hands over to the CD0F keyboard-input
routines. This routine is entered at C2CF after a command
execution, and at the end of a BASIC program. It carries
on thus:
C2D5 - set vector at (5) to 100
C2DC - set line number to 0
C2E0 - set BRK vector to C9D8
C2EA - set error pointer to C9E7
C2F2 - set stack pointer to FF
C2F5 - zero the temporary X and Y stores
C2FB - set nesting level of all GOSUB, FOR, DO loops to 0
C301 - sets all labels to 0
C309 asks "is this a line number"; C313 - YES;
C316 - NO.
This area can be entered anywhere if there is a command
in the input buffer. |
| C31B
to C333 |
Executes the command THEN |
| C325
to C333 |
Executes the command LET |
| C334
to C33E |
Executes the command PRINT |
| C33F
to C3B1 |
PRINT in hexadecimal. Entry at C349
prints the workspace stack in hex. See example, chapter
6. |
| C3B2
to C3C7 |
Executes the command LINK |
| C3C8
to C3E4 |
A subroutine to evaluate the value of an
arbitrarily complex function pointed to by (5),Y and
store the computed value on the workspace stack. On
return the current value of the workspace stack pointer
is where the answer is stored. The value is also copied
to 52,53,54,55. On return the (5),Y pointer has been
consolidated, i.e. (5),0 points to the last character in
the string interpreted. |
