X-Git-Url: https://git.xandkar.net/?a=blobdiff_plain;f=src%2Fhope_fun.erl;h=df0d786e18799a50c74a3a815f50cd7dd75a78ef;hb=cb14ad76f3cc386bce964e822733e5cb9e011ed8;hp=5ee6730499fa840d7a88ab427d4a82126d070673;hpb=e033aadea66cc7f68e3a66cde23a2edfe4c4e9e6;p=hope.git

diff --git a/src/hope_fun.erl b/src/hope_fun.erl
index 5ee6730..df0d786 100644
--- a/src/hope_fun.erl
+++ b/src/hope_fun.erl
@@ -3,6 +3,10 @@
 -export(
     [ id/1
     , curry/1
+    , compose/1  % alias for compose_right/1
+    , compose_right/1
+    , compose_left/1
+    , thread/2
     ]).
 
 -spec id(A) ->
@@ -13,7 +17,7 @@ id(X) ->
 -spec curry(fun()) ->
     fun().
 curry(F) ->
-    {value, {arity, Arity}} = lists:keysearch(arity, 1, erlang:fun_info(F)),
+    {arity, Arity} = erlang:fun_info(F, arity),
     curry(F, [], Arity).
 
 -spec curry(fun(), list(), integer()) ->
@@ -22,3 +26,32 @@ curry(F, Args, 0) ->
     apply(F, lists:reverse(Args));
 curry(F, Args, Arity) ->
     fun (X) -> curry(F, [X | Args], Arity - 1) end.
+
+-spec compose([fun((A) -> B)]) ->
+    fun((A) -> B).
+compose(Fs) ->
+    compose_right(Fs).
+
+-spec compose_right([fun((A) -> B)]) ->
+    fun((A) -> B).
+compose_right(Fs) ->
+    compose_given_fold(Fs, fun lists:foldr/3).
+
+-spec compose_left([fun((A) -> B)]) ->
+    fun((A) -> B).
+compose_left(Fs) ->
+    compose_given_fold(Fs, fun lists:foldl/3).
+
+-spec thread([fun((A) -> B)], A) ->
+    B.
+thread(Fs, X) ->
+    F = compose_left(Fs),
+    F(X).
+
+
+%% ============================================================================
+
+-spec compose_given_fold([fun((A) -> B)], fun((fun((A, B) -> C), B, [A]) -> C)) ->
+    fun((A) -> C).
+compose_given_fold(Fs, Fold) ->
+    fun (X) -> Fold(fun (F, Y) -> F(Y) end, X, Fs) end.