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(), tail, tl(), list differnce, --, and list sum, ++.

[reason7@localhost ~]$ erl

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) Assume Q=[[a,b],[a,b]]. Is the head of Q equal to the tail of Q? Why/why not? Does there exist any list whose tail is equal to its head? Why/why not?

2) Is the length of A++B always longer than either A or B? Can you give a counter example?

3) Is the lenght of A--B always shorter than A? Can you give a counter example?