add and use PureOp

2 files changed, 59 insertions, 1 deletions

diff --git a/alv/base/init.moon b/alv/base/init.moon
index 0cab7e3..65730a3 100644
--- a/alv/base/init.moon
+++ b/alv/base/init.moon
@@ -6,6 +6,7 @@
 --
 -- @module base
 -- @see Op
+-- @see PureOp
 -- @see Builtin
 -- @see FnDef
 -- @see Input
@@ -24,6 +25,7 @@
 -- @see Error
 
 import Op from require 'alv.base.op'
+import PureOp from require 'alv.base.pureop'
 import Builtin from require 'alv.base.builtin'
 import FnDef from require 'alv.base.fndef'
 import Input from require 'alv.base.input'
@@ -34,7 +36,7 @@ import RTNode from require 'alv.rtnode'
 import Error from require 'alv.error'
 
 {
-  :Op
+  :Op, :PureOp
   :Builtin
   :FnDef
   :Input
diff --git a/alv/base/pureop.moon b/alv/base/pureop.moon
new file mode 100644
index 0000000..ea3b810
--- /dev/null
+++ b/alv/base/pureop.moon
@@ -0,0 +1,56 @@
+----
+-- Stateless Operator base for pure functions.
+--
+-- All arguments can be evt- and val-capable. If one of the arguments is an
+-- !-stream, it will be the only `Input.hot`. If there are no !-streams,
+-- all inputs are hot. Passing more than one !-stream is an argument error.
+--
+-- To use `PureOp`, extend the class and set/implement only `pattern`, `type`
+-- and `tick`.
+-- @classmod PureOp
+import Op from require 'alv.base.op'
+import Input from require 'alv.base.input'
+import SigStream, EvtStream from require 'alv.result'
+import Error from require 'alv.error'
+
+unpack or= table.unpack
+
+class PureOp extends Op
+--- members.
+-- @section members
+
+  --- the argument pattern.
+  --
+  -- Must resolve to a simple sequence-table (depth 1).
+  --
+  -- @tfield match.Pattern pattern
+  @pattern: nil
+
+  --- the result type.
+  -- @tfield type.Type type
+  @type: nil
+
+  --- set up inputs for a range of things.
+  setup: (inputs) =>
+    args = @@pattern\match inputs
+
+    local trigger
+    for arg in *args
+      if arg.result.metatype == '!'
+        assert not trigger, Error 'argument', "pure op can take at most one !-stream."
+        trigger = arg
+
+    if trigger
+      super for a in *args
+        if a == trigger
+          Input.hot trigger
+        else
+          Input.cold a
+      @out = EvtStream @@type
+    else
+      super [Input.hot a for a in *args]
+      @out or= SigStream @@type
+
+{
+  :PureOp
+}