The language used here is FP.
I don't understand the difference between the use of <> and [].
For example:
2 : <3,4,5> -> 4
But
+ o [1,2] : <2,3> -> 5
Why is the first sequence written with [] instead of <> ?
Thanks!
The answer to your question is actually in the wiki link you provided. While <...> is used as notation for lists (e.g., <3,4,5> is a list with elements 3, 4, and 5), [...] is just syntax for a functional that is already provided by FP. It is called construction and defined by
[f1, ..., fn]:x = <f1:x, ..., fn:x>
If you are familiar with Haskell: it is similar to
map (\f -> f x) [f1, ..., fn] = [f1 x, ..., fn x]
that is to say, that [...] is some kind of map function, see also Higher order function to apply many functions to one argument.
In your specific examples
2:<3, 4, 5>
selects the second element of the given list, and + o [1, 2]:<2, 3> can be "evaluated" as
follows (where o is function composition):
+ o [1, 2]:<2, 3> => (definition of composition)
+:([1, 2]:<2, 3>) => (definition of construction)
+:<1:<2, 3>, 2:<2, 3>> => (select list elements)
+:<2, 3> => (addition)
5