KOS_OP_CHECK_EXCEPTION

• Style: LABEL. Arg = target pc (post-compile).

• Stack: Pop TOS (exception type or tuple of types). If current exception matches that value, leave PC unchanged; else set PC to arg (branch to next handler).

• Invariants: Jump locality for target. Used inside exception handling path.

• Compiler form: Pre-compile arg = string label (next handler or re-raise); post-compile arg = pc.

Example: In except block: type(s) on stack; pop and match; jump if no match.

index	opcode	arg	arg view	comment
3	CONST	0	0 (typ)	stack: […, typ]
4	CHECK_EXCEPTION	7	7 (-> 7)	pop typ; if exc not match → pc=7
5	POP	1	1	consume exc
6	RETURN	1	1	handle
7	LABEL	–	–	re-raise or next handler

9.1 Switch dispatch

Switch dispatch opcodes implement multi-way equality branching. A typical checks region runs comparisons in order: each comparison falls through when it does not match so the next check can run without re-pushing the scrutinee. A match jumps into a shared body (or the same body for several keys).

KOS_OP_SWITCH_EQ compares two stack operands, discriminant left below key right (TOS). On match, both are popped and the PC is set to arg (the body). On mismatch, only right is popped; left remains so the following code can push another key and use another SWITCH_EQ.

The single-slot variants (SWITCH_EQ_CONST, SWITCH_EQ_VAR, …) compare the scrutinee s at TOS to an RHS from the extra row. On match, s is popped and the PC jumps to a0. On mismatch, the stack is unchanged and execution falls through.

See compile/switch for the surface form and Switch dispatch (§9.1) for the opcode family.