X-Git-Url: https://git.xandkar.net/?a=blobdiff_plain;f=src%2Fhope_list.erl;h=abfb3d39ca74aa61f38a360ef502b5e1a2f7d6a9;hb=refs%2Ftags%2F2.1.0;hp=aba9944f9d5b7ee53c2a3a0a73ee52f3a3e76e34;hpb=2a81fbac3178e649d03519f7b1b25e43d7850713;p=hope.git

diff --git a/src/hope_list.erl b/src/hope_list.erl
index aba9944..abfb3d3 100644
--- a/src/hope_list.erl
+++ b/src/hope_list.erl
@@ -6,15 +6,66 @@
 
 -export(
     [ unique_preserve_order/1
+    , map/2
+    , map/3  % Tunable recursion limit
     , map_rev/2
     , map_slow/2
     ]).
 
 
+-define(DEFAULT_RECURSION_LIMIT, 1000).
+
+
 -type t(A) ::
     [A].
 
 
+%% @doc Tail-recursive equivalent of lists:map/2
+%% @end
+-spec map([A], fun((A) -> (B))) ->
+    [B].
+map(Xs, F) ->
+    map(Xs, F, ?DEFAULT_RECURSION_LIMIT).
+
+-spec map([A], fun((A) -> (B)), RecursionLimit :: non_neg_integer()) ->
+    [B].
+map(Xs, F, RecursionLimit) ->
+    map(Xs, F, RecursionLimit, 0).
+
+map([], _, _, _) ->
+    [];
+map([X1], F, _, _) ->
+    Y1 = F(X1),
+    [Y1];
+map([X1, X2], F, _, _) ->
+    Y1 = F(X1),
+    Y2 = F(X2),
+    [Y1, Y2];
+map([X1, X2, X3], F, _, _) ->
+    Y1 = F(X1),
+    Y2 = F(X2),
+    Y3 = F(X3),
+    [Y1, Y2, Y3];
+map([X1, X2, X3, X4], F, _, _) ->
+    Y1 = F(X1),
+    Y2 = F(X2),
+    Y3 = F(X3),
+    Y4 = F(X4),
+    [Y1, Y2, Y3, Y4];
+map([X1, X2, X3, X4, X5 | Xs], F, RecursionLimit, RecursionCount) ->
+    Y1 = F(X1),
+    Y2 = F(X2),
+    Y3 = F(X3),
+    Y4 = F(X4),
+    Y5 = F(X5),
+    Ys =
+        case RecursionCount > RecursionLimit
+        of  true  -> map_slow(Xs, F)
+        ;   false -> map     (Xs, F, RecursionLimit, RecursionCount + 1)
+        end,
+    [Y1, Y2, Y3, Y4, Y5 | Ys].
+
+
 %% @doc lists:reverse(map_rev(L, F))
 %% @end
 -spec map_slow([A], fun((A) -> (B))) ->
@@ -23,7 +74,8 @@ map_slow(Xs, F) ->
     lists:reverse(map_rev(Xs, F)).
 
 
-%% @doc O(N), tail-recursive equivalent to lists:rev(lists:map(F, L))
+%% @doc Tail-recursive alternative to lists:map/2, which accumulates and
+%% returns list in reverse order.
 %% @end
 -spec map_rev([A], fun((A) -> (B))) ->
     [B].