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14:11:16
pjb
Some would say that (loop for line = (read-line stream nil nil) while line) is idiomatic. Personally, I don't have problem eliding the explicit test for NIL in lisp. However, in C I started to test explicitely for NULL when testing pointers, because 0 as a symbol representing the null pointer is true only in some context. Notably, and horribly, when as argument to a function, 0 is not interpreted as the null pointer, but as an in
14:13:27
pjb
For example, CL:AND and CL:OR are very explicitely defined to return the first or last values of the argument expressions. So using (or var :default) or (and (predicatep foo) foo) are perfectly readable, just as: (loop while line) is.
14:16:58
beach
pjb: That's one leap you just made. Essentially, you are saying that anything that is semantically well defined by the language is readable to the maintainer.
14:18:06
TMA
I even use '\0' in comparisons because of the intent is more apparent (and while '\0' is equivalent to 0 in C, it is not in C++); the same goes in lisp: make the intent apparent, preferably without needless reference to something external
15:43:37
beach
My guess is that the first C compiler was not terribly smart, so you had to write code like that to get the best performance. That changed with GCC.
15:49:12
madrik
Maybe it's just looking to the past, but I get a kick out of thinking that there used to be implementations of other languages besides Lisp on the Lisp machines.
15:50:41
dlowe
I've wondered if it'd be possible to do FFI in sbcl by providing a libc implementation that used underlying sbcl code, so that allocated memory would be gc'd as usual
15:51:45
dlowe
as far as I know, all the CL implementations keep non-CL code in its own little space
16:03:18
pjb
schweers: well, since char are upgraded to int when passed as parameter and in other places it's essentially the same.
16:04:37
pjb
The difference would be '\0'+'\1' = (char)1 instead of 0+'\1' = (int)1, but againm since (char)1 would be upgraded, I don't remember any circumstance where it would make a difference. (but there may still be one obscur case).
16:07:06
pjb
(let ((s #(1 2 3 4)) (d #(1 2 3 0)) (i 0) (j 0)) (loop :while (= (prog1 (aref s i) (incf i)) (prog1 (aref d j) (incf j)))) (list i j)) #| --> (4 4) |#
16:08:23
pjb
(let ((s #(1 2 3 0)) (d (vector 0 0 0 0)) (i 0)) (loop :while (prog1 (plusp (setf (aref d i) (aref s i))) (incf i))) d) #| --> #(1 2 3 0) |#
16:09:04
pjb
(let ((s #(1 2 3 0)) (d (vector 0 0 0 0)) (i 0) (j 0)) (loop :while (prog1 (plusp (setf (aref d i) (aref s j))) (incf i) (incf j))) d) #| --> #(1 2 3 0) |#
19:16:31
phoe
I have two trees of CLOS instances that form a cyclic graph. How can I compare them for equality? For slot values that are not standard instances, I'd like to use EQUAL; for slot values that are standard instances, I want to recurse while marking the instances I have already visited to avoid loops.
19:16:53
phoe
These instances are of different types; I also want to ensure that the respective instances are of the same type.
19:18:16
pjb
If you have associations that have a multiplicity more than 1, then there could be an abiguity, and you might need backtracking.
19:18:58
pjb
Otherwise, you will need a walk of the two graphs. You can keep the nodes that are already walked in a hash-table.
19:20:11
phoe
All instances have some sort of ID however, so I can sort them by that ID in each list and then assume that the order is the same.
19:20:48
phoe
Or, whenever I traverse one graph, I get the ID of the current instance, find the matching instance in the other graph, and use that instance for comparing the slot values.
19:20:51
pjb
Then you will have to backtrack. If you have a->nb and A->nB and a=A, then you will have to try n*(n-1) b=B.
19:21:27
phoe
Will I have to, if they are ordered? I can treat these collections as ordered, meaning that 1st element of one collection must be equal to 1st element of the other collection.
19:22:24
pjb
phoe: well, that depends if the two graph share the same nodes, or only nodes that are equal?
19:23:17
pjb
Ok. Then yes, you can have a subalgorithm to match the list of nodes in the same association.
19:24:55
pjb
There were a couple of math libraries developed in Japan. Perhaps they had something about graph, I'm not sure.