How does foldl work?
With foldl , the function argument takes a default value, the first element of the list, and returns a new default value. When the list is empty, that default value will be the result of the fold.
Is foldl or foldr more efficient?
If you know that you’ll have to traverse the whole list no matter what (e.g., summing the numbers in a list), then foldl’ is more space- (and probably time-) efficient than foldr .
How do I find the length of a list in Erlang?
You can use length() to find the length of a list, and can use list comprehensions to filter your list. num(L) -> length([X || X <- L, X < 1]).
What are the two types of lists available in Erlang?
Erlang: tuples and lists
- tuples deal with heterogeneous values, while lists are homegeneous.
- Tuples and lists are pattern-matched differently (we’ll see more of this when writing pattern matching code, of course).
- Tuples have O(1) random access, while lists have O(N) random access, being built of cons cells.
What is the difference between foldl and foldr?
The only difference between foldl and foldr is the recursive case. foldl immediately invokes function f on the first list item x and the base value v . The result of this invocation ( f v x ) is passed as the new base value to foldl . The following two functions are used to debug foldl and foldr .
How do I split a List in Erlang?
You can use lists:split/2 for this: divide(L, N) -> divide(L, N, []). divide([], _, Acc) -> lists:reverse(Acc); divide(L, N, Acc) when length(L) < N -> lists:reverse([L|Acc]); divide(L, N, Acc) -> {H,T} = lists:split(N, L), divide(T, N, [H|Acc]).
Which functions are used to access the head and tail of the list in Erlang?
The first element of a list is named the Head, and the rest of the list is named the Tail. We will use two built-in functions (BIF) to get them.
How do I split a list in Erlang?
What is foldl and foldr in Haskell?
I like to call foldr as “fold from the right”, while foldl is “fold from the left”. As you can see, for foldl the position of the seed value is on the left hand side of the tree, while foldr seed value is on the right hand side of the tree. …
What Is a Racket foldr?
foldl and foldr both act as reducers on lists, using proc to “fold” each item of the list in turn into the initial value init .