Because the world wasn't weird enough already I took the liberty to
implement goto in picolisp. This works by using a "trampoline" based on
'throw and 'catch, each goto makes the evaluation "bounce" and continue
from the point of the next label until it falls trough.
(de goto (L)
(throw 'goto L) )
(de prog+ "Prg"
(use ("Thunk" "Ret" "L")
(setq "Thunk" "Prg" "Ret" NIL)
(while
(catch 'goto
(setq "Ret" (run "Thunk")) )
(setq "L" @
"Thunk" (seek '[(X) (= (car X) "L")] "Prg") ) )
"Ret") )
(====)
Labels should be atoms (though they can be anything that can be
compared with = and would have no side effect when evaluated.)
A couple examples:
Nested loop:
(prog+
(zero I J)
loop:
(prinl I "," J)
(when (< (inc 'I) 4)
(goto 'loop:) )
(when (< (inc 'J) 4)
(zero I)
(goto 'loop:) ) )
Infinite loop:
(prog+
10 (prinl "cyborg_ar is a genius!")
20 (goto 10) )
"Computed" goto:
(prog+
(goto 'ask:)
err:
(prinl "^JSorry, i quite didn't get that...")
ask:
(prinl "Choose a number from 0-3:")
(goto (or (min (format (line)) 4) 'err:))
0 (prinl "You chose zero.") (goto 'end:)
1 (prinl "You chose one.") (goto 'end:)
2 # Fall trough
3 (prinl "You chose two or three.") (goto 'end:)
4 (goto 'err:)
end:
(prinl "Bye!") )
Cheers,
José
PS: I leave the implementation of COMEFROM as an exercise for the
reader.
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