diff --git a/fold.cm b/fold.cm
index a686c844..40592713 100644
--- a/fold.cm
+++ b/fold.cm
@@ -4,6 +4,7 @@
 var fold = function(ast) {
   var scopes = ast.scopes
   var nr_scopes = length(scopes)
+  ast._diagnostics = []
 
   var type_tag_map = {
     array: "array", record: "record", text: "text",
@@ -701,8 +702,30 @@ var fold = function(ast) {
         name = stmt.left.name
         if (name != null) {
           sv = scope_var(fn_nr, name)
-          if (sv != null && sv.nr_uses == 0 && is_pure(stmt.right)) {
-            stmt.dead = true
+          if (sv != null && sv.nr_uses == 0) {
+            if (is_pure(stmt.right)) stmt.dead = true
+            if (stmt.right != null && stmt.right.kind == "(" && stmt.right.expression != null && stmt.right.expression.name == "use") {
+              push(ast._diagnostics, {
+                severity: "warning",
+                line: stmt.left.from_row + 1,
+                col: stmt.left.from_column + 1,
+                message: `unused import '${name}'`
+              })
+            } else if (stmt.kind == "def") {
+              push(ast._diagnostics, {
+                severity: "warning",
+                line: stmt.left.from_row + 1,
+                col: stmt.left.from_column + 1,
+                message: `unused constant '${name}'`
+              })
+            } else {
+              push(ast._diagnostics, {
+                severity: "warning",
+                line: stmt.left.from_row + 1,
+                col: stmt.left.from_column + 1,
+                message: `unused variable '${name}'`
+              })
+            }
           }
         }
       }
@@ -715,6 +738,12 @@ var fold = function(ast) {
         sv = scope_var(fn_nr, stmt.name)
         if (sv != null && sv.nr_uses == 0) {
           stmt.dead = true
+          push(ast._diagnostics, {
+            severity: "warning",
+            line: stmt.from_row + 1,
+            col: stmt.from_column + 1,
+            message: `unused function '${stmt.name}'`
+          })
         }
       }
       if (stmt.dead != true) push(out, stmt)
@@ -1028,9 +1057,22 @@ var fold = function(ast) {
   // Remove dead top-level functions
   var live_fns = []
   var fn = null
+  var fn_sv = null
   fi = 0
   while (fi < length(ast.functions)) {
     fn = ast.functions[fi]
+    if (fn.name != null) {
+      fn_sv = scope_var(0, fn.name)
+      if (fn_sv != null && fn_sv.nr_uses == 0) {
+        fn.dead = true
+        push(ast._diagnostics, {
+          severity: "warning",
+          line: fn.from_row + 1,
+          col: fn.from_column + 1,
+          message: `unused function '${fn.name}'`
+        })
+      }
+    }
     if (fn.dead != true) {
       push(live_fns, fn)
     }
diff --git a/internal/engine.cm b/internal/engine.cm
index ff384479..009172b6 100644
--- a/internal/engine.cm
+++ b/internal/engine.cm
@@ -158,6 +158,7 @@ function analyze(src, filename) {
   var line = null
   var col = null
   var has_errors = _ast.errors != null && length(_ast.errors) > 0
+  var folded = null
   if (has_errors) {
     while (_i < length(_ast.errors)) {
       e = _ast.errors[_i]
@@ -176,7 +177,17 @@ function analyze(src, filename) {
     }
     disrupt
   }
-  return fold_mod(_ast)
+  folded = fold_mod(_ast)
+  if (!_no_warn && folded._diagnostics != null && length(folded._diagnostics) > 0) {
+    _i = 0
+    while (_i < length(folded._diagnostics)) {
+      e = folded._diagnostics[_i]
+      os.print(`${filename}:${text(e.line)}:${text(e.col)}: ${e.severity}: ${e.message}\n`)
+      _i = _i + 1
+    }
+  }
+  folded._diagnostics = null
+  return folded
 }
 
 // Lazy-loaded verify_ir module (loaded on first use)