Erlang (programming language)/Tutorials/Command Line

Getting to know the erlang command line.

Erlang has a command line like lisp, python and prolog. In the erlang command line you may not reuse a variable, unless you force it to forget with f(). f() makes it forget all variables. Let us do some simple list manipulations at the command line with head, hd(), and tail, tl().

[reason7@localhost ~]$ erl
Eshell V5.5  (abort with ^G)

1> L = [b,c,d,5].
[b,c,d,5]

2> hd(L) = b

3> H = [f,t].
[f,t]

4> H++L.
[f,t,b,c,d,5]

5> Q = [[a,b],[a,b]].
[[a,b],[a,b]]

6> hd(Q).
[a,b]

7> tl(Q).
[ [a,b ] ]

Questions:

1) If Q=[[a,b],[a,b]] is the head of Q equal to the tail of Q? why?

2) Is the length of A++B always longer the either A or B?

3) Is the lenght of A--B always shorter than A?