9.3.6.10 Miscellaneous Instructions

Instruction: nop

Does nothing! Used for padding other instructions to certain alignments.

Instruction: halt

Exits the VM, returning a SCM value. Normally, this instruction is only part of the “bootstrap program”, a program run when a virtual machine is first entered; compiled Scheme procedures will not contain this instruction.

If multiple values have been returned, the SCM value will be a multiple-values object (see section Returning and Accepting Multiple Values).

Instruction: break

Does nothing, but invokes the break hook.

Instruction: drop

Pops off the top value from the stack, throwing it away.

Instruction: dup

Re-pushes the top value onto the stack.

Instruction: void

Pushes “the unspecified value” onto the stack.

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