Behaviour Preservation across Code Versions in Erlang

Algorithm 3

string.erl (original and optimized versions).

Original version

(1) tokens(S, Seps) ->

(2)  tokens1(S, Seps, []).

(3) tokens1([C∣S], Seps, Toks) ->

(4)  case member(C, Seps) of

(5)   true ->

(6)   tokens1(S, Seps, Toks);

(7)   false ->

(8)   tokens2(S, Seps, Toks, [C])

(9)  end;

(10) tokens1([], _Seps, Toks) ->

(11)  reverse(Toks).

(12) tokens2([C∣S], Seps, Toks, Cs) ->

(13)  case member(C, Seps) of

(14)   true ->

(15)   tokens1(S, Seps, [reverse(Cs)∣Toks]);

(16)   false ->

(17)   tokens2(S, Seps, Toks, [C∣Cs])

(18)  end;

(19) tokens2([], _Seps, Toks, Cs) ->

(20)  reverse([reverse(Cs)∣Toks]).

Optimized version

(1) tokens(S, Seps) ->

(2)  case Seps of

(3)   [] ->

(4)    case S of

(5)     [] -> [];

(6)     [_∣_] -> [S]

(7)    end;

(8)   [C] ->

(9)     tokens_single_1(reverse(S), C, []);

(10)   [_∣_] ->

(11) tokens_multiple_1(reverse(S), Seps, [])

(12)  end.

(13) tokens_single_1([Sep∣S], Sep, Toks) ->

(14)  tokens_single_1(S, Sep, Toks);

(15) tokens_single_1([C∣S], Sep, Toks) ->

(16)  tokens_single_2(S, Sep, Toks, [C]);

(17) tokens_single_1([], _, Toks) ->

(18)  Toks.

(19) tokens_single_2([Sep∣S], Sep, Toks, Tok) ->

(20)  tokens_single_1(S, Sep, [Tok∣Toks]);

(21) tokens_single_2([C∣S], Sep, Toks, Tok) ->

(22)  tokens_single_2(S, Sep, Toks, [C∣Tok]);

(23) tokens_single_2([], _Sep, Toks, Tok) ->

(24)  [Tok∣Toks].

(25) tokens_multiple_1([C∣S], Seps, Toks) ->

(26)  case member(C, Seps) of

(27)  true ->

(28)   tokens_multiple_1(S, Seps, Toks);

(29)  false ->

(30)   tokens_multiple_2(S, Seps, Toks, [C])

(31)  end;

(32) tokens_multiple_1([], _Seps, Toks) ->

(33)  Toks.

(34) tokens_multiple_2([C∣S], Seps, Toks, Tok) ->

(35)  case member(C, Seps) of

(36)  true ->

(37)   tokens_multiple_1(S, Seps, [Tok∣Toks]);

(38)  false ->

(39)   tokens_multiple_2(S, Seps, Toks, [C∣Tok])

(40)  end;

(41) tokens_multiple_2([], _Seps, Toks, Tok) ->

(42)  [Tok∣Toks].