drain - impl + docstring + test

src/hyperfiddle/electric/impl/runtime_de.cljc

@@ -190,6 +190,11 @@
 
 (def fixed-signals (comp (partial m/signal i/combine) i/fixed))
 
+(defn drain [incseq]
+  (m/ap
+    (m/amb (i/empty-diff 0)
+      (do (m/?> incseq) (m/amb)))))
+
 (def peer-slot-input 0)
 (def peer-slot-store 1)
 (def peer-slots 2)

src/hyperfiddle/electric_de.cljc

@@ -63,7 +63,14 @@ Syntax :
 Stabilizes successive states of collection `xs` with function `kf`. Returns each item as a table.
 " [f xs] `(join (i/diff-by ~f (join (i/items (pure ~xs))))))
 
-;; (defmacro drain [expr] `(join (i/drain (pure ~expr))))
+(defmacro drain "
+Syntax :
+```clojure
+(drain expr)
+```
+Samples and discards `expr` synchronously with changes. Returns nothing.
+" [expr] `(join (r/drain (pure ~expr))))
+
 (defmacro client [& body] `(::lang/site :client ~@body))
 (defmacro server [& body] `(::lang/site :server ~@body))
 

test/hyperfiddle/electric/impl/runtime_test.cljc

@@ -120,4 +120,13 @@
                   [x y])))
   % := {:degree 1, :permutation {}, :grow 1, :shrink 0, :change {0 [[1 0] [2 0] [2 1]]}, :freeze #{}}
   (swap! !n inc)
-  % := {:degree 1, :permutation {}, :grow 0, :shrink 0, :change {0 [[1 0] [2 0] [2 1] [3 0] [3 1] [3 2]]}, :freeze #{}})
+  % := {:degree 1, :permutation {}, :grow 0, :shrink 0, :change {0 [[1 0] [2 0] [2 1] [3 0] [3 1] [3 2]]}, :freeze #{}})
+
+(tests
+  (def !x (atom 0))
+  (on-diff! rcf/tap
+    (root-frame (e/drain (rcf/tap (e/watch !x)))))
+  % := 0
+  % := {:degree 0, :permutation {}, :grow 0, :shrink 0, :change {}, :freeze #{}}
+  (swap! !x inc)
+  % := 1)