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Unbreak the three example programs the RND merge left behind
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Adding native RND and ASC (ae2c702) made RND a function name, and a suffixed
identifier that collides with one is refused -- "SYNTAX ERROR Reserved word in
variable name". Three example programs held their PRNG output in a variable
called RND#, or a host field called RND%, and none of them had run since:

  - examples/galaga/ bound RND% as a host field on both ENEMY and GAME. The
    BASIC-visible name is ROLL% now; the C member stays `rnd`. This one was
    caught by example_galaga and example_galaga_interop, which have been
    failing.
  - examples/breakout/characters/breakout.bas and examples/megademo/
    megademo.bas both use RND# for their LCG output, renamed to ROLL#. Neither
    is in any test, so neither failure was visible.

examples/breakout/sprites/breakout.bas was broken a second way: seven REM lines
the reader refuses. Worth recording that the ceiling is not the one the message
names -- src/sink_stdio.c fails when the read filled the buffer without seeing
a terminator, so with AKBASIC_MAX_LINE_LENGTH at 80 the message says "79
character limit" and the real maximum is 78, because a 79-character line leaves
no room for the newline. The sweeps that fixed the corpus and the megademo for
this did not reach this file. The seven comments are reflowed.

The prose went stale with the code. Chapter 21 said "there is no RND verb in
this dialect; issue #16 tracks adding one", chapter 17's historical aside
offered an LCG that no longer parses, and four REM blocks across the two games
said the same thing. All of them now say RND exists, and say why these programs
keep their own generator anyway: the sequence has to be reproducible for a
headless run to be the same game on every machine, which is what lets
interop_test.c assert exact counts.

Chapter 21 also gains the rule that bit them, since a reader writing a host
type will hit it: a host field name is a bare word and shares a namespace with
every verb and function.

None of this came from the submodule bump -- all three were already broken on
main. It was found by running the tutorial games, which nothing else does;
that gap is akbasic issue #58.

Verified: all three run clean under the dummy drivers, and 114/114 default,
116/116 with akgl.

Co-Authored-By: Andrew Kesterson <andrew@aklabs.net>
Co-Authored-By: Claude Code (Claude Opus 5, claude-opus-5[1m]) <noreply@anthropic.com>
This commit is contained in:
Tachikoma
2026-08-05 23:26:33 -04:00
parent a15e172c2a
commit 13f1df03ef
10 changed files with 84 additions and 53 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
docs/17-tutorial-breakout.md
View File

@@ -1049,17 +1049,17 @@ every program. It remains a useful from-scratch PRNG example:
```basic norun
SEED# = 12345
RMAX# = 6
RND# = 0
ROLL# = 0
I# = 0
FOR I# = 1 TO 5
GOSUB RANDOM
PRINT "ROLL " + (RND# + 1)
PRINT "ROLL " + (ROLL# + 1)
NEXT I#
END
LABEL RANDOM
SEED# = MOD(((SEED# * 1103515245) + 12345), 2147483648)
RND# = MOD((SEED# / 65536), RMAX#)
ROLL# = MOD((SEED# / 65536), RMAX#)
RETURN
```

37
docs/21-tutorial-galaga-enemies.md
View File

@@ -20,7 +20,7 @@ whole development loop; the engine never rebuilds.
- **[Step 2](#step-2-bind-the-engines-own-actor)** — bind the engine's own
actor as the second type, which is the point of the whole exercise
- **[Step 3](#step-3-share-the-frame-and-the-dice)** — share the frame state,
and give the script randomness it cannot make itself
and hand the script dice the engine controls
- **[Step 4](#step-4-why-bindings-and-not-arguments)** — see why the structures
are bindings rather than function arguments
- **[Step 5](#step-5-the-shape-of-the-script)** — learn the three language
@@ -75,7 +75,7 @@ typedef struct galaga_Enemy
float t; /* parametric clock for the current maneuver */
int32_t hp;
int32_t fire; /* outbox: script sets 1, engine consumes */
float rnd; /* inbox: engine writes fresh 0..1 each call */
float rnd; /* inbox: fresh 0..1 each call; ROLL% in BASIC */
} galaga_Enemy;
```
@@ -107,7 +107,7 @@ static const akbasic_HostField ENEMY_FIELDS[] = {
AKBASIC_HOST_FIELD( galaga_Enemy, t, "T%", AKBASIC_HOSTFIELD_FLOAT ),
AKBASIC_HOST_FIELD( galaga_Enemy, hp, "HP#", AKBASIC_HOSTFIELD_INT32 ),
AKBASIC_HOST_FIELD( galaga_Enemy, fire, "FIRE#", AKBASIC_HOSTFIELD_INT32 ),
AKBASIC_HOST_FIELD( galaga_Enemy, rnd, "RND%", AKBASIC_HOSTFIELD_FLOAT )
AKBASIC_HOST_FIELD( galaga_Enemy, rnd, "ROLL%", AKBASIC_HOSTFIELD_FLOAT )
};
static const akbasic_HostType ENEMY_TYPE = {
"ENEMY", sizeof(galaga_Enemy), ENEMY_FIELDS, 8
@@ -194,7 +194,7 @@ typedef struct galaga_Shared
float playerx; /* the player actor's position, this frame */
float playery;
int32_t wave;
float rnd; /* fresh 0..1 each frame; the issue #16 route */
float rnd; /* fresh 0..1 each frame; ROLL% to the script */
} galaga_Shared;
```
@@ -203,13 +203,24 @@ the engine refreshes it at the top of every frame. The boss reads
`GAME@.PLAYERX%` to lead its dive; the fire decision reads it to know whether
anything is worth shooting at.
The `rnd` fields — one here per frame, one on each enemy per call — exist
because the engine's PRNG is the script's **only** source of randomness: write
`SELF@.RND% < DT% * 1.5` and an enemy's trigger finger is a dice roll. There
is no `RND` verb in this dialect; issue #16 tracks adding one, and Chapter
17's breakout hand-rolls a linear congruential generator in BASIC as the other
route. Here the engine fills the field, which also keeps a headless run the
same game on every machine — the PRNG is the example's own, not libc's.
The `rnd` fields — one here per frame, one on each enemy per call — carry the
engine's PRNG into the script: write `SELF@.ROLL% < DT% * 1.5` and an enemy's
trigger finger is a dice roll.
The dialect does now have a native `RND` function — issue #16 closed, and
[Chapter 12](12-function-reference.md) documents it — so this is no longer the
*only* route; Chapter 17's breakout hand-rolls a linear congruential generator
in BASIC as a third. The engine keeps filling the field here on purpose,
because it buys something `RND` cannot: the numbers come from the example's own
PRNG rather than libc's, so a headless run is the same game on every machine,
which is what makes `example_galaga` a test and not just a demo.
**The BASIC name is `ROLL%`, not `RND%`.** A host field is a bare word and
shares a namespace with every verb and function, so once `RND` became a
function name a field could no longer be called that — the scanner refuses it
with *"Reserved word in variable name"*. The C member stays `rnd`; only the
name the script sees had to move. [Chapter 16](16-structures.md) has the same
rule for `TYPE` declarations.
## Step 4: Why bindings, and not arguments
@@ -351,7 +362,7 @@ DEF DECIDEFIRE(DT%)
DX% = GAME@.PLAYERX% - ACTOR@.X%
IF ABS(DX%) > 140 THEN RETURN 0
IF ACTOR@.Y% > GAME@.PLAYERY% THEN RETURN 0
IF SELF@.RND% < DT% * 1.5 THEN SELF@.FIRE# = 1
IF SELF@.ROLL% < DT% * 1.5 THEN SELF@.FIRE# = 1
RETURN 0
END
```
@@ -386,7 +397,7 @@ DEF UPDATEBEE(DT%)
IF (S# AND 2) > 0 THEN BEGIN
ACTOR@.X% = SELF@.HOMEX% + SIN(SELF@.T% * 1.7) * 16
ACTOR@.Y% = SELF@.HOMEY%
IF SELF@.RND% < DT% * 0.04 THEN SELF@.STATE# = 4 : SELF@.T% = 0
IF SELF@.ROLL% < DT% * 0.04 THEN SELF@.STATE# = 4 : SELF@.T% = 0
BEND
IF (S# AND 4) > 0 THEN BEGIN
R# = DIVESTEP(DT%, 130, 0.2)

16
examples/breakout/characters/breakout.bas
View File

@@ -145,7 +145,7 @@ RX# = 0
N# = 0
MROW# = 0
RMAX# = 2
RND# = 0
ROLL# = 0
SND# = 0
P$ = ""
H$ = ""
@@ -172,7 +172,8 @@ BSG$(4) = "[--]"
BSG$(5) = "[--]"
REM --- the seed -------------------------------------------------------
REM There is no RND in this dialect. TI# is jiffies off the host's clock
REM RND exists now, but this program keeps its own LCG so a headless run
REM is the same game every time. TI# is jiffies off the host's clock
REM and is host uptime rather than zero-based, which makes it a fine seed.
SEED# = TI#
@@ -389,17 +390,18 @@ BY# = PY# - 10
RMAX# = 2
GOSUB RANDOM
BVX# = BSPD#
IF RND# = 0 THEN BVX# = 0 - BSPD#
IF ROLL# = 0 THEN BVX# = 0 - BSPD#
BVY# = 0 - BSPD#
PDEC# = 0
GOSUB SHOWSPR
RETURN
REM A linear congruential generator, because this dialect has no RND.
REM A linear congruential generator. RND(n) would do this in one token
REM now; the LCG stays because its sequence is reproducible.
REM The multiply stays inside int64 for any seed under 2^31.
LABEL RANDOM
SEED# = MOD(((SEED# * 1103515245) + 12345), 2147483648)
RND# = MOD((SEED# / 65536), RMAX#)
ROLL# = MOD((SEED# / 65536), RMAX#)
RETURN
REM ####################################################################
@@ -632,7 +634,7 @@ NUDGE# = 0
STALL# = 0
RMAX# = 4
GOSUB RANDOM
BVX# = (RND# * 3) - 6
BVX# = (ROLL# * 3) - 6
IF BVX# = 0 THEN BVX# = 3
RETURN
@@ -641,7 +643,7 @@ REM like something with a hand on the paddle rather than a mirror.
LABEL DEMOAIM
RMAX# = 81
GOSUB RANDOM
DOFF# = RND# - 40
DOFF# = ROLL# - 40
RETURN
REM ####################################################################

29
examples/breakout/sprites/breakout.bas
View File

@@ -241,7 +241,8 @@ SLX# = 0
SLY# = 0
SLI# = 0
REM The two eraser stamps. Declared here for exactly the same reason -- built
REM inside DRAWPROTOS and left undeclared, they were SHAPE:6 and SHAPE:7 inside
REM inside DRAWPROTOS and left undeclared, they were SHAPE:6 and SHAPE:7
REM inside
REM it and empty everywhere else.
BL$ = ""
HBL$ = ""
@@ -254,10 +255,13 @@ REM cursor through every DATA item in the program in the order they appear
REM in the file, so whichever loader runs first gets the DATA that is
REM written first. The tables are written first.
REM The text layer repaints every row it owns, opaque, so it has to be moved
REM out of the way before anything drawn can be seen. Two rows at the bottom is
REM out of the way before anything drawn can be seen. Two rows at the bottom
REM is
REM enough for the final score, and hands the other thirty-five to the drawing
REM verbs. Everything this game draws then simply stays there -- a drawing goes
REM into a layer the frame composites, so nothing here is captured into a sprite
REM verbs. Everything this game draws then simply stays there -- a drawing
REM goes
REM into a layer the frame composites, so nothing here is captured into a
REM sprite
REM and nothing is redrawn every frame.
WINDOW 0, 35, 49, 36
@@ -293,7 +297,8 @@ ENVELOPE 0, 0, 6, 0, 4
TEMPO 12
COLLISION 2, BRICKHIT
REM The stamps, once. They used to be rebuilt whenever the SSHAPE pool ran dry,
REM The stamps, once. They used to be rebuilt whenever the SSHAPE pool ran
REM dry,
REM because every frame's capture spent another slot; nothing captures now, so
REM eight slots are spent here and never again.
GOSUB DRAWPROTOS
@@ -374,7 +379,8 @@ COLOR 1, 1
FOR K# = 0 TO 15
DRAW 1, 0, 130 + K# TO 67, 130 + K#
NEXT K#
REM And an eighth the width of the HUD strip, for the same reason: the strip is
REM And an eighth the width of the HUD strip, for the same reason: the strip
REM is
REM rewritten whenever a number in it changes, and the old digits have to go
REM somewhere first.
FOR K# = 0 TO 59
@@ -393,7 +399,8 @@ DPLAY# = 1
DHUD# = 1
RETURN
REM Take one brick off the screen: stamp the blank over it. Called when a brick
REM Take one brick off the screen: stamp the blank over it. Called when a
REM brick
REM breaks, so the field is never redrawn as a whole during play -- which is
REM what lets the whole live-list machinery go.
LABEL ERASEBRICK
@@ -444,7 +451,8 @@ WIDTH 1
COLOR 0, 1 : COLOR 1, 4 : COLOR 2, 8 : COLOR 3, 5
COLOR 4, 11 : COLOR 5, 16 : COLOR 6, 6
REM The old strip goes first. Nothing here clears the screen -- a drawing
REM stays, which is the whole point -- so the digits that were there have to be
REM stays, which is the whole point -- so the digits that were there have to
REM be
REM stamped over before the new ones are drawn.
Z$ = HBL$
GSHAPE Z$, 0, 0
@@ -495,7 +503,10 @@ IF SNDON# = 0 THEN VOL 0
RETURN
LABEL PRESSPAUSE
IF STATE# = 2 THEN STATE# = 6 : GMTYP# = 0 : BAN$ = "PAUSED" : GOSUB SETBANNER : RETURN
IF STATE# <> 2 THEN GOTO PRESSPAUSE2
STATE# = 6 : GMTYP# = 0 : BAN$ = "PAUSED" : GOSUB SETBANNER
RETURN
LABEL PRESSPAUSE2
IF STATE# = 6 THEN STATE# = 2 : BAN$ = "" : GOSUB SETBANNER
RETURN

13
examples/galaga/enemies.c
View File

@@ -71,10 +71,15 @@ static char *ENEMY_CHARACTER[GALAGA_ENEMY_KINDS] = {
/* --------------------------------------------------------------- random --- */
/*
* No RND verb exists (issue #16), so the engine is the script's only source
* of randomness: it refreshes GAME@.RND% each frame and SELF@.RND% each call
* from this PRNG. A hand-rolled LCG rather than rand() so a headless run is
* the same game on every libc.
* The engine is this script's source of randomness: it refreshes GAME@.ROLL%
* each frame and SELF@.ROLL% each call from this PRNG. A hand-rolled LCG
* rather than rand() so a headless run is the same game on every libc, which
* is what lets interop_test.c assert exact counts. The dialect gained a native
* RND (issue #16) after this example was written; the field stays because RND
* would reintroduce exactly the per-machine variation this avoids.
*
* The BASIC-visible name is ROLL%, not RND%: host field names share a
* namespace with verbs and functions, so RND stopped being available as one.
*/
static uint32_t PRNG_STATE = 0x12345678u;

8
examples/galaga/galaga.bas
View File

@@ -50,7 +50,7 @@ DEF DECIDEFIRE(DT%)
DX% = GAME@.PLAYERX% - ACTOR@.X%
IF ABS(DX%) > 140 THEN RETURN 0
IF ACTOR@.Y% > GAME@.PLAYERY% THEN RETURN 0
IF SELF@.RND% < DT% * 1.5 THEN SELF@.FIRE# = 1
IF SELF@.ROLL% < DT% * 1.5 THEN SELF@.FIRE# = 1
RETURN 0
REM Bee: enter, breathe in formation, occasionally dive nearly straight.
@@ -65,7 +65,7 @@ DEF UPDATEBEE(DT%)
IF (S# AND 2) > 0 THEN BEGIN
ACTOR@.X% = SELF@.HOMEX% + SIN(SELF@.T% * 1.7) * 16
ACTOR@.Y% = SELF@.HOMEY%
IF SELF@.RND% < DT% * 0.04 THEN SELF@.STATE# = 4 : SELF@.T% = 0
IF SELF@.ROLL% < DT% * 0.04 THEN SELF@.STATE# = 4 : SELF@.T% = 0
BEND
IF (S# AND 4) > 0 THEN BEGIN
R# = DIVESTEP(DT%, 130, 0.2)
@@ -85,7 +85,7 @@ DEF UPDATEBFLY(DT%)
IF (S# AND 2) > 0 THEN BEGIN
ACTOR@.X% = SELF@.HOMEX% + SIN(SELF@.T% * 2.1) * 24
ACTOR@.Y% = SELF@.HOMEY%
IF SELF@.RND% < DT% * 0.05 THEN SELF@.STATE# = 4 : SELF@.T% = 0
IF SELF@.ROLL% < DT% * 0.05 THEN SELF@.STATE# = 4 : SELF@.T% = 0
BEND
IF (S# AND 4) > 0 THEN BEGIN
R# = DIVESTEP(DT%, 260, 0.1)
@@ -108,7 +108,7 @@ DEF UPDATEBOSS(DT%)
IF (S# AND 2) > 0 THEN BEGIN
ACTOR@.X% = SELF@.HOMEX% + SIN(SELF@.T% * 1.1) * 10
ACTOR@.Y% = SELF@.HOMEY%
IF SELF@.RND% < DT% * 0.03 THEN SELF@.STATE# = 4 : SELF@.T% = 0
IF SELF@.ROLL% < DT% * 0.03 THEN SELF@.STATE# = 4 : SELF@.T% = 0
BEND
IF (S# AND 4) > 0 THEN BEGIN
R# = DIVESTEP(DT%, 60, 0.9)

4
examples/galaga/galaga.h
View File

@@ -77,7 +77,7 @@ typedef struct galaga_Enemy
float t; /* parametric clock for the current maneuver */
int32_t hp;
int32_t fire; /* outbox: script sets 1, engine consumes */
float rnd; /* inbox: engine writes fresh 0..1 each call */
float rnd; /* inbox: fresh 0..1 each call; ROLL% in BASIC */
} galaga_Enemy;
/** @brief Frame state every enemy may read. Bound once as GAME@. */
@@ -86,7 +86,7 @@ typedef struct galaga_Shared
float playerx; /* the player actor's position, this frame */
float playery;
int32_t wave;
float rnd; /* fresh 0..1 each frame; the issue #16 route */
float rnd; /* fresh 0..1 each frame; ROLL% to the script */
} galaga_Shared;
/* --------------------------------------------------------------- screens --- */

3
examples/galaga/main.c
View File

@@ -491,7 +491,8 @@ static akerr_ErrorContext *frame(bool *running)
}
/* The shared frame state, refreshed before any enemy thinks. The engine
* filling GAME@.RND% is the issue #16 route: no RND verb exists. */
* fills GAME@.ROLL% from its own PRNG rather than letting the script call
* the native RND, so a headless run is the same game on every machine. */
galaga_shared.playerx = galaga_game.player->x + 50.0f;
galaga_shared.playery = galaga_game.player->y;
galaga_shared.rnd = galaga_random();

4
examples/galaga/script.c
View File

@@ -62,7 +62,7 @@ static const akbasic_HostField ENEMY_FIELDS[] = {
AKBASIC_HOST_FIELD( galaga_Enemy, t, "T%", AKBASIC_HOSTFIELD_FLOAT ),
AKBASIC_HOST_FIELD( galaga_Enemy, hp, "HP#", AKBASIC_HOSTFIELD_INT32 ),
AKBASIC_HOST_FIELD( galaga_Enemy, fire, "FIRE#", AKBASIC_HOSTFIELD_INT32 ),
AKBASIC_HOST_FIELD( galaga_Enemy, rnd, "RND%", AKBASIC_HOSTFIELD_FLOAT )
AKBASIC_HOST_FIELD( galaga_Enemy, rnd, "ROLL%", AKBASIC_HOSTFIELD_FLOAT )
};
static const akbasic_HostType ENEMY_TYPE = {
"ENEMY", sizeof(galaga_Enemy), ENEMY_FIELDS, 8
@@ -87,7 +87,7 @@ static const akbasic_HostField GAME_FIELDS[] = {
AKBASIC_HOST_FIELD( galaga_Shared, playerx, "PLAYERX%", AKBASIC_HOSTFIELD_FLOAT ),
AKBASIC_HOST_FIELD( galaga_Shared, playery, "PLAYERY%", AKBASIC_HOSTFIELD_FLOAT ),
AKBASIC_HOST_FIELD( galaga_Shared, wave, "WAVE#", AKBASIC_HOSTFIELD_INT32 ),
AKBASIC_HOST_FIELD( galaga_Shared, rnd, "RND%", AKBASIC_HOSTFIELD_FLOAT )
AKBASIC_HOST_FIELD( galaga_Shared, rnd, "ROLL%", AKBASIC_HOSTFIELD_FLOAT )
};
static const akbasic_HostType GAME_TYPE = {
"GAME", sizeof(galaga_Shared), GAME_FIELDS, 4

17
examples/megademo/megademo.bas
View File

@@ -10,7 +10,7 @@ REM A demoscene production for the akbasic interpreter, written as if
REM it were 1985 and this dialect were the machine under the tree.
REM It leans on every corner of the interpreter on purpose:
REM
REM - there is no RND, so it carries chapter 17's LCG and seeds it
REM - it carries chapter 17's LCG rather than the native RND, and seeds it
REM from the jiffy clock
REM - the palette cannot be rewritten, so every "colour cycle" is an
REM honest redraw of the same strokes in the next colour
@@ -81,7 +81,7 @@ REM machine and a predeclared scratch variable occupies one forever,
REM where a scoped one gives its slot back. The first cut of this
REM program predeclared everything and ran the pool dry.
RMAX# = 0
RND# = 0
ROLL# = 0
TX% = 0
TB# = 0
@@ -816,11 +816,12 @@ REM =====================================================================
REM Subroutines.
REM =====================================================================
REM Chapter 17's generator, verbatim: there is no RND in this dialect.
REM Answers 0 to RMAX#-1 in RND#, from the middle bits of the seed.
REM Chapter 17's historical generator, verbatim. RND(n) is built in now;
REM this stays so the demo runs identically on every machine.
REM Answers 0 to RMAX#-1 in ROLL#, from the middle bits of the seed.
LABEL RANDOM
SEED# = MOD(((SEED# * 1103515245) + 12345), 2147483648)
RND# = MOD((SEED# / 65536), RMAX#)
ROLL# = MOD((SEED# / 65536), RMAX#)
RETURN
REM NS# stars in four brightnesses. Two LCG pulls a star, and the
@@ -830,10 +831,10 @@ SI# = 0
DO WHILE SI# < NS#
RMAX# = W#
GOSUB RANDOM
X# = RND#
X# = ROLL#
RMAX# = H#
GOSUB RANDOM
Y# = RND#
Y# = ROLL#
B# = MOD(SEED#, 4)
COLOR 1, STC#(B#)
DRAW 1, X#, Y#
@@ -1291,7 +1292,7 @@ LABEL REHOME
MOVSPR L2#, 0.5 * W#, 0.5 * H#
RMAX# = 360
GOSUB RANDOM
SBG#(L2#) = RND#
SBG#(L2#) = ROLL#
MOVSPR L2#, SBG#(L2#) # 5
RETURN