[m-rev.] diff: more efficient library functions for Erlang backend

[Peter Wang]

Branches: main

library/list.m:
	Override list.reverse with a more efficient version for Erlang.

library/string.m:
	Add efficient implementations of semidet_from_char_list/2,
	sub_string_search_start/4 and substring/4 for Erlang.


Index: library/list.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/library/list.m,v
retrieving revision 1.163
diff -u -r1.163 list.m
--- library/list.m	13 Feb 2007 00:16:57 -0000	1.163
+++ library/list.m	6 Jul 2007 08:01:35 -0000
@@ -1609,6 +1609,13 @@
 list.reverse_2([X | Xs], L0, L) :-
     list.reverse_2(Xs, [X | L0], L).
 
+:- pragma foreign_proc("Erlang",
+    list.reverse(L0::in, L::out),
+    [will_not_call_mercury, promise_pure, thread_safe],
+"
+    L = lists:reverse(L0)
+").
+
 %-----------------------------------------------------------------------------%
 
 list.sort(L0, L) :-
Index: library/string.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/library/string.m,v
retrieving revision 1.261
diff -u -r1.261 string.m
--- library/string.m	6 Jun 2007 02:09:44 -0000	1.261
+++ library/string.m	6 Jul 2007 08:01:35 -0000
@@ -1356,6 +1356,15 @@
     Str[size] = '\\0';
 }").
 
+:- pragma foreign_proc("Erlang",
+    string.semidet_from_char_list(CharList::in, Str::uo),
+    [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
+        does_not_affect_liveness],
+"
+    Str = CharList,
+    SUCCESS_INDICATOR = true
+").
+
 :- pragma promise_equivalent_clauses(string.semidet_from_char_list/2).
 
 string.semidet_from_char_list(CharList::in, Str::uo) :-
@@ -1693,6 +1702,22 @@
     SUCCESS_INDICATOR = (Index >= 0);
 }").
 
+:- pragma foreign_proc("Erlang",
+    sub_string_search_start(WholeString::in, Pattern::in, BeginAt::in,
+        Index::out),
+    [will_not_call_mercury, promise_pure, thread_safe],
+"
+    String = lists:nthtail(BeginAt, WholeString),
+    case string:str(String, Pattern) of
+        0 ->
+            Index = -1,
+            SUCCESS_INDICATOR = false;
+        Match ->
+            Index = BeginAt + Match - 1,
+            SUCCESS_INDICATOR = true
+    end
+").
+
 % This is only used if there is no matching foreign_proc definition
 sub_string_search_start(String, SubString, BeginAt, Index) :-
     sub_string_search_start_2(String, SubString, BeginAt, length(String),
@@ -3988,6 +4013,24 @@
     }
 }").
 
+:- pragma foreign_proc("Erlang",
+    string.substring(Str::in, Start0::in, Count::in, SubString::uo),
+    [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
+        does_not_affect_liveness],
+"
+    Start =
+        if
+            Start0 < 0 -> 0;
+            true -> Start0
+        end,
+    if
+        Count =< 0 ->
+            SubString = """";
+        true ->
+            SubString = string:substr(Str, 1 + Start, Count)
+    end
+").
+
 :- pragma foreign_proc("C",
     string.unsafe_substring(Str::in, Start::in, Count::in, SubString::uo),
     [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
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