So I've been bugfixing and merging the code from the simplified operators branch. I just fixed so that UNDEFINED is always ignored when adding arrays, mappins and multisets, and not just as first argument.

Previously:

Pike v8.1 release 6 running Hilfe v3.5 (Incremental Pike Frontend)

`+( UNDEFINED, ({1}), ({2}) );

(1) Result: ({ /* 2 elements */ 1, 2 })

`+( ({1}), UNDEFINED, ({2}) );

Bad argument 2 to `+(). Expected array. Unknown program: `+(({1}),UNDEFINED,({2})) HilfeInput:1: HilfeInput()->___HilfeWrapper()

The remaining issue I have is what to do when an addition LFUN returns UNDEFINED. I interpret Pers commit message as he was leaning towards having an object return UNDEFINED mean to not involve the object, though there was no code to back that up. I lean towards having returning UNDEFINED be an error, since the object can just as well return the value it was given. In any event, the current behaviour is wrong:

Pike v8.1 release 6 running Hilfe v3.5 (Incremental Pike Frontend)

class A { mixed ``+(mixed x) { return UNDEFINED; } } `+( ({1}), A(), ({2}) );

(1) Result: ({ /* 1 element */ 2 })