Hi Folks,
Thank you for your responses. They are surprising.
In the functional language Haskell, there is a clear disadvantage of appending
an item onto the end of a list, and developers are strongly encouraged to build
lists by prepending an item onto a list. For example, this prepending approach
is strongly _preferred_:
[3]
2:[3]
1:[2,3]
This results in creating the list: [1,2,3]
This appending approach is strongly _discouraged_:
[1]
[1] ++ [2]
[1,2] ++ [3]
This results in creating the same list: [1,2,3]
Here is what one Haskell book says:
Watch out when repeatedly using the ++ operator on long strings. When you put
together two lists (even if you append a singleton list to a list, for
instance: [1,2,3] ++ [4]), internally, Haskell has to walk through the whole
list on the left side of ++. That's not a problem when dealing with lists that
aren't too big. But putting something at the end of a list that's fifty million
entries long is going to take a while. However, putting something at the
beginning of a list using the : operator (also called the cons operator) is
instantaneous.
'A':" SMALL CAT"
"A SMALL CAT"
5:[1,2,3,4,5]
[5,1,2,3,4,5]
Notice how : takes a number and a list of numbers or a character and a list of
characters, whereas ++ takes two lists. Even if you're adding an element to the
end of a list with ++, you have to surround it with square brackets so it
becomes a list.
I vaguely recall that Lisp behaving the same way (as Haskell) and with the same
recommendation to build lists from the left not the right.
Why is XSLT different from these other functional languages?
/Roger
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