Exceptions and Context Managers

Abscom adds Python-style try/catch/end_try exception control flow plus a with context-manager macro, all on the var object model.

#include "abscom/abs.h"

How exceptions work

throw records a message and unwinds to the innermost active try. The global abs_last_error holds the thrown error object (an ABS_ERROR value) so the catch clause can inspect it. Each try/end_try pair is balanced: the macro pushes a jmp_buf on an internal stack (depth 10) and end_try pops it, so nested and sibling try blocks coexist. An uncaught throw prints the message and calls exit(1).

var divide(long a, long b) {
    if (b == 0) throw("Division by zero!");
    return v(a / b);
}

var result = None;
try {
    result = divide(10, 2);
    print(v("Success:"), result);            /* 5 */
}
catch (result) {
    print(v("Caught:"), result);             /* only on throw */
}
end_try;

The catch macro takes the variable name that receives the caught error. Because C++ reserves try/catch/throw as keywords, the exception API is C-only (#ifndef __cplusplus).

with — automatic resource cleanup

with(VAR, INIT) evaluates the initializer, runs the body exactly once, then calls close_resource(VAR). close_resource closes ABS_FILE objects and nulls the file pointer so a later close_file is a no-op — no double close.

Macro	Description
with(VAR, INIT)	Run INIT, execute the body once, then close_resource(VAR).
close_resource(var obj)	Free a var's resource (fcloses ABS_FILE objects).

with (f, fopen_safe("hello.txt", "w")) {
    if (is_err(f)) throw("Could not open file!");
    write_file(f, v("Hello with-macro!"));
}
/* f is closed automatically; the block ran exactly once */

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