Add Stream.resource/3

Author: José Valim

CHANGELOG.md

@@ -6,6 +6,7 @@
   * [Kernel] Add `Enum.reverse/2`
   * [Kernel] Implement `defmodule/2`, `@/1`, `def/2` and friends in Elixir itself. `case/2`, `try/2` and `receive/1` have been made special forms. `var!/1`, `var!/2` and `alias!/1` have also been implemented in Elixir and demoted from special forms
   * [Record] Support dynamic fields in `defrecordp`
+  * [Stream] Add `Stream.resource/3`
   * [Typespec] Support `is_var/1` in typespecs
 
 * Bug fixes

lib/elixir/lib/file.ex

@@ -970,36 +970,31 @@ defmodule File do
     modes = open_defaults(modes, true)
     bin   = nil? List.keyfind(modes, :encoding, 0)
 
-    fn(acc, fun) ->
-      case F.open(path, modes) do
-        { :ok, device }    -> device
-        { :error, reason } ->
-          raise File.Error, reason: reason, action: "stream", path: to_string(path)
+    start_fun =
+      fn ->
+        case F.open(path, modes) do
+          { :ok, device }    -> device
+          { :error, reason } ->
+            raise File.Error, reason: reason, action: "stream", path: to_string(path)
+        end
       end
 
-      try do
-        case bin do
-          true  -> IO.binstream(device, line_or_bytes, acc, fun)
-          false -> IO.stream(device, line_or_bytes, acc, fun)
-        end
-      after
-        F.close(device)
+    next_fun =
+      case bin do
+        true  -> &IO.do_binstream(&1, line_or_bytes)
+        false -> &IO.do_stream(&1, line_or_bytes)
       end
-    end
+
+    Stream.resource(start_fun, next_fun, &F.close/1)
   end
 
   @doc false
   def binstream!(file, mode // [], line_or_bytes // :line) do
     IO.write "File.binstream! is deprecated, simply use File.stream! instead\n" <>
              Exception.format_stacktrace
-    fn(fun, acc) ->
-      device = open!(file, mode)
-      try do
-        IO.binstream(device, line_or_bytes, fun, acc)
-      after
-        F.close(device)
-      end
-    end
+    Stream.resource(fn -> open!(file, mode) end,
+                    &IO.do_binstream(&1, line_or_bytes),
+                    &F.close/1)
   end
 
   @doc """

lib/elixir/lib/io.ex

@@ -244,7 +244,7 @@ defmodule IO do
   """
   @spec stream(device, :line | pos_integer) :: Enumerable.t
   def stream(device, line_or_codepoints) do
-    fn(acc, f) -> stream(map_dev(device), line_or_codepoints, acc, f) end
+    Stream.unfold(map_dev(device), &do_stream(&1, line_or_codepoints))
   end
 
   @doc """
@@ -257,30 +257,30 @@ defmodule IO do
   """
   @spec binstream(device, :line | pos_integer) :: Enumerable.t
   def binstream(device, line_or_bytes) do
-    fn(acc, f) -> binstream(map_dev(device), line_or_bytes, acc, f) end
+    Stream.unfold(map_dev(device), &do_binstream(&1, line_or_bytes))
   end
 
   @doc false
-  def stream(device, what, acc, fun) do
+  def do_stream(device, what) do
     case read(device, what) do
       :eof ->
-        acc
+        nil
       { :error, reason } ->
         raise IO.StreamError, reason: reason
       data ->
-        stream(device, what, fun.(data, acc), fun)
+        { data, device }
     end
   end
 
   @doc false
-  def binstream(device, what, acc, fun) do
+  def do_binstream(device, what) do
     case binread(device, what) do
       :eof ->
-        acc
+        nil
       { :error, reason } ->
         raise IO.StreamError, reason: reason
       data ->
-        binstream(device, what, fun.(data, acc), fun)
+        { data, device }
     end
   end