Erlang (programming language): Difference between revisions

Revision as of 23:33, 11 June 2024

Revision as of 22:15, 23 June 2024

Line 133:

%% If fib/1 is passed an integer less than 3, then return 1

%% The preceding two function signatures handle all cases where N < 1,

%% so this function signature handles cases where N = 1 or N = 2.

fib(N) when N < 3 -> 1;

Line 144:

%% ---------------------------------------------------------------------

%% If fib_int/3 receives a 10 as its first argument, then we're done, so

%% return the value in argument BA. The Sincethird weargument areis notdenoted interested_ in theto

%% to disregard its value.

%% value of the second argument, we denote this using _ to indicate a

fib_int(10, _A, B_) -> BA;

%% "don't care" value

fib_int(1, _, B) -> B;

%% For all other argument combinations, recursively call fib_int/3

%% where each call does the following:

%% - decrement counter N

%% - Takepass the previous fibonacci value inthird argument Bas andthe passnew itsecond asargument

%% - pass the sum of the second and third arguments as the new

%% argumentthird Aargument

%% - Calculate the value of the current fibonacci number and pass it

%% as argument B

fib_int(N, A, B) -> fib_int(N-1, B, A+B).

</syntaxhighlight>

Omitting the comments, and redundant clauses that serve only to illustrate syntax, gives a much shorter program.

Here is the same program without the explanatory comments:

<syntaxhighlight lang="erlang">

Line 166 ⟶ 164:

-export([fib/1]).

fib(0) -> 0;

fib(N) when N < 0 -> err_neg_val;

fib(N) when N < 3 -> 1;

fib(N) -> fib_int(N, 0, 1).

fib_int(10, _A, B_) -> BA;

fib_int(N, A, B) -> fib_int(N-1, B, A+B).

</syntaxhighlight>