.NH 1
Editing Functions
.PP
Function editing on
\*u \*a
differs from that on other
\*a systems.
The ``del'' character is not used.
Instead,
the \*u editor
is used.
There are two alternatives.
.PP
The ``)editf'' system command is
used to edit a function residing
in the internal workspace.
The command
.sp
	)editf fn
.sp
writes the function ``fn'' into
a temporary file and calls
the editor to process it.
When the editor is finished,
\*a reads it back in.
.PP
The command:
.sp
	)edit junk
.sp
invokes the editor to process
the \*u file ``junk''.
When the editor is terminated
via the ``q'' command,
control returns to \*a,
which will read ``junk'' into
the internal workspace.
Note that
this method involves files
external to \*a.
``)editf'' is generally a better choice
since it allows all information relating
to the workspace to be contained
within the workspace.
.PP
Because of the way in which editing
is performed,
there are two points which need
special attention.
First,
it is not possible to edit a suspended
function.
(For a description of suspended functions
and how to reset them,
see ``The State Indicator''.)
Second,
if the function header
(first line of the function)
contains a syntax error,
\*a will
.I not
read in the function.
In general,
this means that the function
is no longer defined in the
workspace,
and the only other copy
exists in a temporary file.
In order to save you a lot
of work retyping,
\*a will
automatically copy the temporary
file into a file called
``apl.badfn''
.PP
An example is probably called for at
this point
to clear the mud somewhat.
The following shows the creation
of the function ``fact''
which computes factorials
by multiplication.
.DS
	)editf fact
	[new fn]
XED
0 lines
>a
[ 0 ]	n { fact+i
[ 1 ]	  n { 1
[ 2 ]	loop: } (i = 0) / 0
[ 3 ]	  n { n X i
[ 4 ]	  i { i - 1
[ 5 ]	  } loop
[ 6 ]	.
>w
>q
n { fact+i
      ^
syntax error
Function saved in apl.badfn
.DE
The error in line 0
(``fact+i'')
caused \*a to stop reading
the function,
so it was automatically copied
to the file ``apl.badfn''.
To get it back,
you can say:
.DS
	)editf fact
	[new fn]
XED
0 lines
>r apl.badfn
5 lines
>0s/+/ /p
[ 0 ]	n { fact i
>w
>q
.DE
.PP
If you use ``)edit'' instead of ``)editf'',
\*a will not worry about saving
the function in ``apl.badfn''
because you were editing from a
\*u file rather than
the internal workspace,
and that file still exists.