CS-SWAP

description:: CS-SWAP "c-s-swap" Interpretation: Interpretation semantics for this word are undefined. Execution: ( C: orig1|dest1 orig2|dest2 -- orig2|dest2 orig1|dest1 ) Swap two elements on top of the control-flow stack. An ambiguous condition exists if there are less than two items, each of which shall be an orig or dest, at the top of the control-flow stack before CS-SWAP is executed.
discussion:: This word was propposed for ANS standardization, but was rejected because it may be added to any standard program with a single line of code: : CS-SWAP 1 CS-ROLL ; On the other hand, the need to invoke CS-ROLL with an argument other than 1 happens very rarely. You do not really need to implement CS-ROLL to implement ELSE : : ELSE POSTPONE AHEAD CS-SWAP POSTPONE THEN ; IMMEDIATE because the implementation-dependent definition of CS-SWAP most likely will be: : CS-SWAP 2SWAP \ assuming double-cell orig's and dest's \ assuming that the control-flow stack is the data stack ;