Tested each sample.

gem/ex10.lua

@@ -0,0 +1,17 @@
+function pump.step(src, snk)
+  local chunk, src_err = src()
+  local ret, snk_err = snk(chunk, src_err)
+  if chunk and ret then return 1
+  else return nil, src_err or snk_err end
+end
+
+function pump.all(src, snk, step)
+    step = step or pump.step
+    while true do
+        local ret, err = step(src, snk)
+        if not ret then
+            if err then return nil, err
+            else return 1 end
+        end
+    end
+end