Erlang (programming language): Difference between revisions

Revision as of 22:15, 23 June 2024

Revision as of 22:48, 4 July 2024

Line 121:

%% The order in which these function signatures are declared is a vital

%% part of this module's functionality

%% If fib/1 is passed precisely the integer 0, then return 0

fib(0) -> 0;

%% If fib/1 receives a negative number, then return the atom err_neg_val

%% Normally, such defensive coding is discouraged due to Erlang's 'Let

%% it Crash' philosophy; however, inbut here the thisresult casewould webe shouldan explicitlyinfinite

%% loop.

%% prevent a situation that will crash Erlang's runtime engine

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

%% If fib/1 is passed anprecisely the integer less than 30, then return 10

fib(0) -> 0;

%% 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;

%% For all other values, call the private function fib_int/3 to perform

%% the calculation

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

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

Line 145 ⟶ 140:

%% If fib_int/3 receives 0 as its first argument, then we're done, so

%% return the value in argument AB. The thirdsecond argument is denoted _ to

%% to disregard its value.

fib_int(0, A_, _B) -> AB;

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

Line 158 ⟶ 153:

</syntaxhighlight>

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

<syntaxhighlight lang="erlang">

Line 164 ⟶ 159:

-export([fib/1]).

fib(N0) when N < 3 -> 10;

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

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

fib_int(0, A_, _B) -> AB;

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

</syntaxhighlight>