tests/language/input/no_device.bas

10 REM SCNCLR goes through the text sink, which every runtime has, so it works
20 REM with no input device attached. GET needs one and must name itself.
30 SCNCLR
40 PRINT "SCNCLR OK"
50 GET A$
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> 2026-07-31 08:35:05 -04:00			`10 REM SCNCLR goes through the text sink, which every runtime has, so it works`
			`20 REM with no input device attached. GET needs one and must name itself.`
			`30 SCNCLR`
			`40 PRINT "SCNCLR OK"`
			`50 GET A$`