Fairy long, I'm afraid, but probably worth reading if you do a lot
of scripting, particularly with lists or matrices.
In working on some scripts lately I've been building lists using
the syntax
list foo = null
loop <something>
...
list foo += varname
...
endloop
This works OK, but I kept forgetting to say "list foo += .."
rather than just "foo += ...". The result was an "unknown
variable in command" error message, which I found confusing at
first, then annoying. (Appearing on the left-hand side of a
genr-type expression, "foo" was not recognized as the name of
anything, unless you prompted gretl to look for lists with the
"list" keyword.)
So I've made a start on incorporating lists into the genr
mechanism more fully. You no longer have to repeat "list" in
front of listnames, as above. Once a list is created, you can add
to it, subtract from it, or redefine it, just using its name.
While working in this area I discovered a bug or two in genr.
For example, up till today, if you typed
scalar x = 3 4
you'd get a scalar x with value 3 and no error message, despite
the syntactically incorrect trailing " 4". No more. Now, one or
more spaces between variables or constants in a genr formula (with
no intervening operator or punctuation) has a specific meaning,
namely, concatenation of list elements. So, the following is OK:
list xlist = 1 2 3
xlist += 4 5 6
But "scalar x = 3 4" will produce an error: it's trying to assign
a list to a scalar.
One side effect is worth noting. According to the manual, the way
to create a matrix out of data series is, e.g.,
matrix m = { x1, x2, x3 }
with the names of the series separated by commas. Up till now,
however, this would also work:
matrix m = { x1 x2 x3 }
This was just sloppiness, and it won't work any more.
The other bug I found was the possible masking of lists by scalars
or series. E.g.
list X = x1 x2 x3
X = log(x1)
The second command would go through without flagging any error:
you'd get a variable named X, but the list named "X" would now be
inaccessible. This can't happen any more:
open data4-10
list X = 1 2 3
X = log(ENROLL)
> Data types not conformable for operation
However, if you replace the third line with
list X = log(ENROLL)
you get the effect you might expect, namely, replacing the
original list with a new one that has one element,
l_ENROLL.
There are no doubt some new issues introduced by this change
that will need to be hashed out. But the warning I gave earlier
about the state of CVS related to breakage of previously valid
uses of genr, and I believe that problem is now fixed.
Allin.
