chore: try macros first

src/Init/Lean/Elab/Term.lean

@@ -480,18 +480,20 @@ partial def elabTermAux (expectedType? : Option Expr) (catchExPostpone := true)
 | stx => withFreshMacroScope $ withIncRecDepth stx $ do
   trace `Elab.step stx $ fun _ => stx;
   s ← get;
-  let table := (termElabAttribute.ext.getState s.env).table;
-  let k := stx.getKind;
-  match table.find? k with
-  | some elabFns => elabTermUsing s stx expectedType? catchExPostpone elabFns
-  | none         => do
-    env  ← getEnv;
-    stx' ← catch
-      (adaptMacro (getMacros env) stx)
-      (fun ex => match ex with
-        | Exception.ex Elab.Exception.unsupportedSyntax => throwError stx ("elaboration function for '" ++ toString k ++ "' has not been implemented")
-        | _                                             => throw ex);
-    withMacroExpansion stx stx' $ elabTermAux stx'
+  env ← getEnv;
+  stxNew? ← catch
+    (do newStx ← adaptMacro (getMacros env) stx; pure (some newStx))
+    (fun ex => match ex with
+      | Exception.ex Elab.Exception.unsupportedSyntax => pure none
+      | _                                             => throw ex);
+  match stxNew? with
+  | some stxNew => withMacroExpansion stx stxNew $ elabTermAux stxNew
+  | _ =>
+    let table := (termElabAttribute.ext.getState s.env).table;
+    let k := stx.getKind;
+    match table.find? k with
+    | some elabFns => elabTermUsing s stx expectedType? catchExPostpone elabFns
+    | none         => throwError stx ("elaboration function for '" ++ toString k ++ "' has not been implemented")
 
 /--
   Main function for elaborating terms.

tests/lean/run/doNotation1.lean

@@ -1,3 +1,19 @@
+open Lean
+
+partial def expandHash : Syntax → StateT Bool MacroM Syntax
+| Syntax.node k args =>
+  if k == `doHash then do set true; `((^MonadState.get))
+  else do
+    args ← args.mapM expandHash;
+    pure $ Syntax.node k args
+| stx => pure stx
+
+@[macro Lean.Parser.Term.do] def expandDo : Macro :=
+fun stx => do
+  (stx, expanded) ← expandHash stx false;
+  if expanded then pure stx
+  else Macro.throwUnsupported
+
 new_frontend
 
 def f : IO Nat :=
@@ -26,3 +42,11 @@ else do
   x ← f;
   y ← g x;
   IO.println y
+
+syntax [doHash] "#":max : term
+
+def tst4 : StateT (Nat × Nat) IO Unit := do
+if #.1 == 0 then
+  IO.println "first field is zero"
+else
+  IO.println "first field is not zero"