Read the keyboard: implement GET, GETKEY and SCNCLR

The poll_key half of group E, against the akbasic_InputBackend record. The
libakgl implementation behind it is akgl_controller_poll_key(), which drains a
ring the library fills from SDL events the host pumps -- so the interpreter can
answer "is there a key waiting" without owning an event loop, which is what goal
3 requires.

GET and GETKEY differ in one way and it is the interesting one. GET takes
whatever is there including nothing, and an empty buffer is success with the
empty string rather than an error -- that is what happens on most iterations of
every GET loop ever written, and upstream is explicit that its poll reports it
the same way. GETKEY waits, and since the library may not block, waiting is
spelled as holding the step loop: the verb sets a flag and akbasic_runtime_step()
declines to advance until a key arrives. Every step still returns and a bounded
run() still comes back, so a host keeps its frame rate; the program simply does
not move past the GETKEY.

The PLAY queue is serviced before that check on purpose -- music should keep
playing while a program waits for a keypress. Withdrawing the input device while
a GETKEY is holding releases it rather than wedging the script on a device that
no longer exists.

Both verbs accept an integer variable as well as a string one and give it the raw
key code, which is what a program testing for cursor or function keys needs. No
key is code zero, matching what a C128 reports. A float variable is refused: it
is neither a character nor a code.

SCNCLR goes through the text sink rather than a device, because the sink is where
PRINT already goes and is the only thing that knows what a screen means for this
host. The stdio sink treats it as a no-op; clearing a pipe means nothing.

One thing worth knowing before writing any bounded-run test, and now commented in
tests/input_verbs.c: source lines are stored indexed by line number and the
cursor starts at zero, so a step is spent on each empty slot along the way. A
program at line 10 needs eleven steps before it has run anything.

70/70 ctest, clean under -Wall -Wextra, doxygen clean.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

This commit is contained in:

Andrew Kesterson

2026-07-31 08:35:05 -04:00

parent e24926d429

commit 83185bafa8

11 changed files with 508 additions and 4 deletions

									
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CMakeLists.txt
									
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				@@ -111,6 +111,7 @@ set(AKBASIC_SOURCES

				  src/runtime_commands.c

				  src/runtime_functions.c

				  src/runtime_graphics.c

				  src/runtime_input.c

				  src/scanner.c

				  src/sink_stdio.c

				  src/symtab.c

				@@ -197,6 +198,7 @@ set(AKBASIC_TESTS

				  error_codes

				  grammar_leaves

				  graphics_verbs

				  input_verbs

				  parser_commands

				  parser_expressions

				  runtime_evaluate

Read the keyboard: implement GET, GETKEY and SCNCLR

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CMakeLists.txt

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