member vs. memq

Aldo,

The best (and only correct) way to modify the second code is to use member instead. You should not use eq/memq with strings (the documentation says that you should only use it with symbols and lists). In general, eq compares the pointer to the object, so would only be successful if the object is exactly the same object. The problem is that if you use eq type checks on strings, it ought to work if you do:

a="aaa"
b=a
c="aaa"

eq(a b) => t

However, the outcome of eq(a c) is a little more uncertain - because there is some optimisation on string storage so that it (sometimes) will smartly avoid double creation of identical strings in memory - however, you are then at the mercy of when that optimisation does or doesn't work. I used to have an example article which showed a very strange case where using memq to compare cell names was dependent upon the presence of a variable assignment later in the code - however, we retired that article a few years after we improved the documentation to make it much more strongly say that you should only use eq/memq on symbols and lists.

Andrew.

BTW, you could use memq if you used concat to convert both strings to be symbols, but I wouldn't advise that as a good approach. For a start, it's unlikely to be any more efficient than using member, and secondly it would pollute the symbol table with arbitrary symbols (and symbols don't get garbage collected).

So don't do this:

mapcar('symbolToString memq(concat("qqq") mapcar('concat parseString("qqq" "www"))))

Andrew.