Simplify the followOutput function

DataflowRewriter/Rewriter.lean

@@ -86,7 +86,7 @@ structure NextNode (Ident) where
   typ : Ident
   connection : Connection Ident
 
-def followOutput (g : ExprHigh String) (inst output : String) : RewriteResult (NextNode String) := do
+def followOutput' (g : ExprHigh String) (inst output : String) : RewriteResult (NextNode String) := do
   let (pmap, _) ← ofOption (.error "instance not in modules")
     <| g.modules.find? inst
   let localOutputName ← ofOption (.error "port not in instance portmap")
@@ -97,4 +97,7 @@ def followOutput (g : ExprHigh String) (inst output : String) : RewriteResult (N
     <| ExprHigh.findInputPort' localInputName g.modules
   ofOption (.error "instance not in modules") <| (g.modules.findEntry? inst).map (λ x => ⟨inst, iport, x.2.1, x.2.2, c⟩)
 
+def followOutput (g : ExprHigh String) (inst output : String) : Option (NextNode String) :=
+  (followOutput' g inst output).toOption
+
 end DataflowRewriter

DataflowRewriter/Rewrites/MergeRewrite.lean

@@ -9,17 +9,16 @@ import DataflowRewriter.ExprHighElaborator
 
 namespace DataflowRewriter.MergeRewrite
 
+/--
+The matcher takes in a dot graph and should return the cluster of nodes that
+form the subgraph as a list of instance names.
+-/
 def matcher (g : ExprHigh String) : RewriteResult (List String) := do
   let (.some list) ← g.modules.foldlM (λ nodes inst (pmap, typ) => do
       if nodes.isSome then return nodes
       unless typ = "merge" do return none
-      let nn ←
-        try followOutput g inst "out0"
-        catch
-          | .error s => return none
-          | .done => throw .done
-      unless nn.typ = "merge" do return none
-      unless nn.inputPort = "inp0" do return none
+      let (.some nn) := followOutput g inst "out0" | return none
+      unless nn.typ = "merge" && nn.inputPort = "inp0" do return none
       return some [inst, nn.inst]
     ) none | throw .done
   return list