Structured Control Flow (Brain Dump)

Note: This is a “brain dump” article, and subject to be cleaned up.

Categories of Structured Control Flow

• Procedure call
  • foo(123, true)
• Terminating
  • return
• Conditional
  • if, if-else, switch
• Looping
  • for - loop with initial statement, condition, post statement, and body
  • for-in - loop with a value to be iterated over
  • while - loop with condition then body
  • do-while - loop with body then condition
• Branching
  • break - go to end outside of the control statement
  • continue - skip to the end of a loop
  • fallthrough - merge two switch case bodies, to have multiple entry points to the merged body
  • Labels on other control flow statements
• Deferred
  • defer/scope(exit)

Pseudo/Partial Categories

• Structured Exception Handling (not specifically Microsoft’s SEH
  • try, catch
• Default (named) return values
  • foo :: proc(x: int) -> (val: int, err: Error) { ... }
• async/await
• yield/resume

Examples of Extensions

Examples in Odin

foo :: proc(x: int) -> (val: int, err: Error) {
	defer if err != nil {
		// handle clean up
	}

	if x > 0 {
		err = .Bad_Error;
	} else {
		val = -x*2 + 1;
	}

	// returns all the named return values without having the manual specify them
	return;
}

the_cases: switch x {
case 1:
	loop: for y > 0 {
		do_thing(&y);
		if y == 3 {
			break the_cases;
		} else if y == 2 {
			continue loop;
		}
		do_other_thing(&y);
	}
case 2, 3:
	do_thing(&y);
	fallthrough;
case 4:
	do_other_thing(&y);
}

Categories of Unstructured Control Flow

• Procedure call
  • x86: Call instruction
• Terminating
  • x86: Return instruction
• Comparison
  • x86: Comparison instructions
• Jump
  • x86: Unconditional jump instructions
  • x86: Conditional jump instructions
  • goto
• Indirect Jump (goto by value)
  • GNU C: Labels as values (jump tables)
• Stack Unwinding (exceptions)
  • longjmp/setjmp
  • Interrupts