Andrew Kesterson
342e4c07da
docs/ and README.md carry 85 fenced blocks. Every one was checked by hand exactly once, when it was written, which is not a standard that survives a changing interpreter -- and four were already wrong: two transcripts showing a leading space PRINT does not emit, akbasic_TextSink in README.md missing the two members it had grown hours earlier, and FILTER's refusal quoted with wording the code does not use. tests/docs_examples.sh reads a fence-tag vocabulary and runs what it finds. BASIC programs and transcripts run and are byte-compared against an `output` block; C snippets compile with -fsyntax-only against the real include path, which CMake writes out because it is transitive through akerror, akstdlib and akgl; shell blocks run in a sandbox. Anything that would reconfigure the build tree, hit the network or re-enter the suite is tagged norun with the reason in MAINTENANCE.md, and the two cmake blocks stay hand-maintained by decision. An untagged block is a failure rather than a default, and the pass line reports what it executed by kind. Both exist because the way a harness like this dies is by quietly matching nothing and passing -- which it duly did on the first CTest run, where a generator expression evaluating to nothing still contributed an empty argument that the script read as a filename. The count is what caught it. The excerpt check earns its own mention: a block tagged `c excerpt=include/akbasic/sink.h` must still appear in that header, comments and whitespace ignored. Compiling it would only redefine the type, so a compile check could not have found the stale struct, and did not. Registered as the CTest case docs_examples in both configurations. Fixing the four wrong examples turned up two interpreter defects, fixed in the previous commit and recorded in TODO.md section 8. MAINTENANCE.md is new: the fence-tag reference, what to do when the case fails, and the conventions that until now only existed inside source comments -- the three test lists and how two of them invert "passed", the sorted verb table, that a golden file is never edited to suit this interpreter, and that a fix gets mutation-checked with a file copy rather than git checkout. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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7. Sound
The sound verbs need the SDL build and an audio device. Without one they refuse by
name, and a machine with no sound card still runs the interpreter — only SOUND and
PLAY fail, and they say so.
SOUND
10 SOUND 1, 4000, 60
Voice, frequency, duration. Voices are numbered from 1. The duration is in jiffies — sixtieths of a second — as on a C128, so 60 is one second.
Further arguments give a frequency sweep: a step, a direction and a range, which is what makes a siren or a laser.
SOUND does not block. On a C128 the note starts and the program carries on; here
the same is true, and it has to be — an embedded interpreter that stopped the host's
frame loop for a second would freeze the game.
PLAY
PLAY takes a string of notes:
10 PLAY "C D E F G"
Within the string:
A to G |
a note |
# $ |
sharp, flat |
O n |
octave |
V n |
voice |
T n |
envelope preset |
U n |
volume |
W, H, Q, I, S |
whole, half, quarter, eighth, sixteenth notes |
R |
rest |
. |
dotted |
Notes are queued and released in time, paced by the host's clock. A program that
PLAYs and then carries on works the way you expect; a program that PLAYs and then
immediately QUITs may not hear all of it.
M — measure — is accepted and does nothing. There is no bar-line accounting to do.
TEMPO
10 TEMPO 8
How fast PLAY releases its queue. The number is the same range a C128 uses; the
constant that turns it into milliseconds is a calibration choice rather than a
transcription, so it may not match a real machine exactly.
ENVELOPE and VOL
10 ENVELOPE 0, 5, 9, 4, 6
20 VOL 8
ENVELOPE defines one of the ten presets PLAY's T selects: attack, decay, sustain
and release. VOL sets the overall volume, 0 to 15.
FILTER
FILTER parses and then refuses at execution:
10 FILTER 1000, 1, 0, 0, 8
? 10 : RUNTIME ERROR FILTER needs a filter stage this device does not have
It sets the SID's filter cutoff, band switches and resonance. The audio backend synthesises raw waveforms and mixes them; there is no filter stage to configure and SDL supplies no primitive to build one from. Refusing is deliberate — a program that asks for a low-pass and gets an unfiltered square wave has been lied to.
This is the one verb still waiting on a capability from the graphics library. It is filed there rather than worked around here.
The clock
Everything with a duration — SOUND, PLAY, TEMPO, and SLEEP from Chapter 2's
neighbourhood — is paced by a clock the host provides. The standalone interpreter
sets it from a monotonic timer every step, so it just works.
An embedded host that never sets the clock gets durations that expire immediately: audible, but never a hang. That is the intended failure direction.