akbasic/src/main.c

/**
 * @file main.c
 * @brief The standalone driver.
 *
 * Everything that belongs to a program rather than to a library lives here: argv
 * handling, sink selection, the unbounded run loop, and a FINISH_NORETURN --
 * which belongs only in a main(). The interpreter library itself never
 * terminates the process.
 *
 * The runtime is static rather than automatic because it carries every pool the
 * interpreter owns -- several megabytes -- and that will not fit on a default
 * stack. An embedding game would place it in its own state for the same reason.
 */

/* clock_gettime and CLOCK_MONOTONIC. C99 alone does not declare either. */
#define _POSIX_C_SOURCE 199309L

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#include <akerror.h>
#include <akstdlib.h>

#include <akbasic/error.h>
#include <akbasic/runtime.h>
#include <akbasic/sink.h>

static akbasic_Runtime RUNTIME;
static akbasic_TextSink SINK;
static akbasic_StdioSink SINKSTATE;

/**
 * @brief Milliseconds off a monotonic clock, for akbasic_runtime_settime().
 *
 * The library reads no clock of its own -- it owns no loop and must not block --
 * so somebody has to tell it what time it is, and for a standalone program that
 * is this. A game does the same thing once a frame off whatever clock it already
 * keeps.
 *
 * Monotonic rather than wall-clock: the interpreter only ever compares these
 * values, and an NTP step backwards in the middle of a tune would hold a note
 * for however long the correction was.
 */
static int64_t monotonic_ms(void)
{
    struct timespec now;

    if ( clock_gettime(CLOCK_MONOTONIC, &now) != 0 ) {
	/*
	 * A clock that cannot be read leaves time frozen, which expires every
	 * duration immediately: the program still runs and the music simply
	 * rushes. Better than refusing to start over a note length.
	 */
	return 0;
    }
    return ((int64_t)now.tv_sec * 1000) + (now.tv_nsec / 1000000);
}

/**
 * @brief Step the interpreter to completion, refreshing the clock as it goes.
 *
 * One step at a time rather than a single unbounded run(), because the driver is
 * the thing that owns the clock: a PLAY string whose notes all measured
 * themselves against a frozen zero would rush the whole tune out at once.
 *
 * A function of its own rather than a loop inside main()'s ATTEMPT, for two
 * reasons that both come from the error protocol. CATCH expands to a `break`, so
 * inside a loop it would escape only the loop and leave the rest of the ATTEMPT
 * running with an error pending. And PASS expands to a `return` of the context,
 * which main() cannot do -- it returns an int. Wrapping the loop is what the
 * protocol prescribes for exactly this shape.
 */
static akerr_ErrorContext AKERR_NOIGNORE *drive(akbasic_Runtime *obj)
{
    PREPARE_ERROR(errctx);

    while ( obj->mode != AKBASIC_MODE_QUIT ) {
	PASS(errctx, akbasic_runtime_settime(obj, monotonic_ms()));
	PASS(errctx, akbasic_runtime_run(obj, 1));
    }
    SUCCEED_RETURN(errctx);
}

int main(int argc, char **argv)
{
    PREPARE_ERROR(errctx);
    FILE *program = NULL;
    int rc = EXIT_SUCCESS;

    ATTEMPT {
	if ( argc > 1 ) {
	    /*
	     * A file argument: read the program from it in RUNSTREAM mode, which
	     * files each line under its line number and then switches to RUN.
	     */
	    CATCH(errctx, aksl_fopen(argv[1], "r", &program));
	    CATCH(errctx, akbasic_sink_init_stdio(&SINK, &SINKSTATE, stdout, program));
	    CATCH(errctx, akbasic_runtime_init(&RUNTIME, &SINK));
	    CATCH(errctx, akbasic_runtime_start(&RUNTIME, AKBASIC_MODE_RUNSTREAM));
	} else {
	    CATCH(errctx, akbasic_sink_init_stdio(&SINK, &SINKSTATE, stdout, stdin));
	    CATCH(errctx, akbasic_runtime_init(&RUNTIME, &SINK));
	    CATCH(errctx, akbasic_runtime_start(&RUNTIME, AKBASIC_MODE_REPL));
	}
	CATCH(errctx, drive(&RUNTIME));
    } CLEANUP {
	if ( program != NULL ) {
	    IGNORE(aksl_fclose(program));
	}
    } PROCESS(errctx) {
    } HANDLE_DEFAULT(errctx) {
	LOG_ERROR_WITH_MESSAGE(errctx, "akbasic terminated on an unhandled error");
	rc = EXIT_FAILURE;
    } FINISH_NORETURN(errctx);

    return rc;
}