Guards
A guard is a sequence of guard expressions, separated by the comma character (,). The whole guard is true if all guard expressions will evaluate to true. A guard can be placed in a function's head, but also in `case ... of` expressions. A guard sequence is a sequence of guards, separated by the semicolon character (;). The guard sequence is true if at least one of the guards is true.
-module(guards).
-compile([export_all]).
age(Age) when Age > 19 ->
adult;
age(Age) when Age >= 13, Age =< 19 ->
teen;
age(Age) when Age >= 3, Age < 13 ->
child;
age(Age) when Age >= 1, Age < 3 ->
toddler.
is_single_digit(N) when N > 0, N < 10;
N =< 0, N > -10 ->
io:format("~p is a single digit integer ~n", [N]);
is_single_digit(N) ->
io:format("Nope, ~p is not a single digit~n", [N]).
run() ->
io:format("A ~p year old is a ~p~n", [1, age(1)]),
io:format("A ~p year old is a ~p~n", [4, age(4)]),
io:format("A ~p year old is a ~p~n", [13, age(13)]),
io:format("A ~p year old is a ~p~n", [21, age(21)]),
is_single_digit(15),
is_single_digit(4),
is_single_digit(-5).
1> c(guards).
{ok,guards}
2> guards:run().
A 1 year old is a toddler
A 4 year old is a child
A 13 year old is a teen
A 21 year old is a adult
Nope, 15 is not a single digit
4 is a single digit integer
-5 is a single digit integer
ok
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