Andrew Kesterson
737fdc760f
ER# held numbers nothing explained. The appendix lists the four error classes the interpreter prints, the eight codes it owns and what raises each, and the codes that reach ER# from errno, libakerror and libakgl underneath it. The table is not asserted. A program in the chapter trips seven of the eight and prints what it got, and docs_examples byte-compares the result -- so the numbers are checked rather than claimed. The eighth, 516, is not usefully trappable and the chapter says why: entering a handler takes a scope, and the pool being empty is what raised it. Two things worth a reader's attention came out of writing it. Two codes register the same ERR() text, so a program must compare the number and print the text. And VAL reports libakerror's Value Error rather than the interpreter's 517, which makes that number the platform's rather than ours -- filed as section 6 item 21, not fixed here, because deciding which libakstdlib failures to translate is a boundary question and ENOENT out of DOPEN is the counter-case. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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12. Function reference
Every function, alphabetically, generated from the interpreter's own dispatch table.
A function is called with parentheses and yields a value; it cannot stand alone as a statement. The arity column is how many arguments it takes — the interpreter checks it, so a call with the wrong number is a syntax error rather than a surprise.
| Function | Args | Form | What it gives |
|---|---|---|---|
ABS |
1 | ABS(n) |
The absolute value of an integer or float. |
ATN |
1 | ATN(n) |
Arctangent, in radians. |
BUMP |
1 | BUMP(1) |
Which sprites have collided, as a bitmask. Reading clears it. |
CHR |
1 | CHR(n) |
The character for a Unicode code point, as a string. |
COS |
1 | COS(n) |
Cosine, in radians. |
ERR |
1 | ERR(n) |
The message text for an error code. ERR(ER#) names the last one. |
HEX |
1 | HEX(n) |
An integer as hexadecimal text. |
INSTR |
2 | INSTR(A$, B$) |
Where B$ appears in A$, counting from zero, or -1. |
LEFT |
2 | LEFT(A$, n) |
The leftmost n characters. Clamped to the string's length. |
LEN |
1 | LEN(x) |
The length of a string, or the element count of an array. |
LOG |
1 | LOG(n) |
Natural logarithm. |
MID |
3 | MID(A$, start, len) |
A substring, counting from zero. |
MOD |
2 | MOD(a, b) |
The remainder of a / b. Integers only. |
PEEK |
1 | PEEK(addr) |
The byte at a real address. |
POINTER |
1 | POINTER(V) |
The address of a variable's value. |
POINTERVAR |
1 | POINTERVAR(V) |
The address of the variable structure itself, metadata included. |
RAD |
1 | RAD(n) |
Degrees converted to radians. |
RGR |
1 | RGR(f) |
The GRAPHIC mode (0), or the drawing surface's width (1) or height (2) in pixels. |
RIGHT |
2 | RIGHT(A$, n) |
The rightmost n characters. Clamped. |
RSPCOLOR |
1 | RSPCOLOR(n) |
One of SPRCOLOR's two shared registers, 1 or 2. |
RSPPOS |
2 | RSPPOS(n, f) |
A sprite's x (0), y (1) or speed (2). |
RSPRITE |
2 | RSPRITE(n, f) |
One of a sprite's SPRITE settings, in SPRITE's argument order. |
SGN |
1 | SGN(n) |
-1, 0 or 1 according to the sign. |
SHL |
2 | SHL(n, bits) |
Shift left. |
SHR |
2 | SHR(n, bits) |
Shift right. |
SIN |
1 | SIN(n) |
Sine, in radians. |
SPC |
1 | SPC(n) |
A string of n spaces. |
STR |
1 | STR(n) |
A number as a string. |
TAN |
1 | TAN(n) |
Tangent, in radians. |
VAL |
1 | VAL(A$) |
A string as a number. Refuses text that is not one. |
XOR |
2 | XOR(a, b) |
Bitwise exclusive or. |
Reserved variables
Two things a C128 exposes as bare names are ordinary global variables here, because this dialect has no variable name without a type suffix:
| Here | On a C128 | Holds |
|---|---|---|
ER# |
ER |
the code of the last trapped error |
EL# |
EL |
the line it happened on |
TI# |
TI |
jiffies — sixtieths of a second — since the host's clock started |
TI$ |
TI$ |
the same time as HHMMSS |
ER# carries this interpreter's error code, not a Commodore error number. There is no
correspondence to reproduce — the errors raised here are not the errors a 1985 ROM
raised — so print ERR(ER#) rather than the number. Chapter 15
lists every value it can hold.