GNU APL:
∇tt
[1] 'aaa
[2] x←1
[3] x←2
[4] x←3
[5] ∇
DEFN ERROR+
∇tt
^
You loose lines 2 3 and 4 too!
IBM APL 2:
∇TT
[1] 'AAA
[2] X←1
[3] X←2
[4] X←3
[5] ∇
TT
SYNTAX ERROR
TT[1] 'AAA
^
In IBM you don't loose anything. It simply tells you where the error is, and you can fix it.
The problem with GNU APL is that it lets you type in a long function without telling you there is a missing quote. When you try to end the edit, the entire function is lost along with all of your typing. IBM lets you type in the error, along with any other error. It is discovered when you execute the function _without_ loosing everything you typed. You can simply fix the line it points to.
Thanks.
Blake