Disallow using syntax-form identifiers as variables.

runtime/src/main/fusion/modules/fusion/procedure.fusion

@@ -176,15 +176,26 @@ Equivalent to `(lambda () body ...)`.
 
 // TODO This should use (provide (rename_out (thunk ||)))
 // but the documentation is wrong.
-  (defpub ||
+  (defpub_syntax ||
     '''
     (|| body ...+)
 
 Returns a zero-argument procedure that evaluates the `body` forms.
 Equivalent to `(lambda () body ...)`.
 
 See also [`|`](fusion/procedure.html#|).
-    ''' thunk)
+    '''
+    (lambda (stx)
+      (let [(body (unsafe_pair_tail (syntax_unwrap stx)))]
+        (if (is_pair body)
+          (datum_to_syntax
+            (pair (quote_syntax lambda)
+                  (pair (quote_syntax ())
+                        body))
+            (quote_syntax context)
+            stx)
+          (wrong_syntax stx "Expected at least one body form")))))
+
 
   (defpub (compose p1 p2)
     '''

runtime/src/main/java/dev/ionfusion/fusion/SyntaxSymbol.java

@@ -305,6 +305,12 @@ SyntaxValue doExpand(Expander expander, Environment env)
                 throw new SyntaxException(null, message, this);
             }
 
+            if (resolveSyntaxMaybe(env) != null)
+            {
+                String message = "Invalid use of syntax form as identifier expression.";
+                throw new SyntaxException(null, message, this);
+            }
+
             Binding b = resolve();
             if (b instanceof FreeBinding)
             {

runtime/src/main/java/dev/ionfusion/fusion/_Private_HelpForm.java

@@ -69,6 +69,7 @@ public void write(Evaluator eval, Appendable out)
     SyntaxValue expand(Expander expander, Environment env, SyntaxSexp stx)
         throws FusionException
     {
+        // TODO reject if not at top level
         final Evaluator eval = expander.getEvaluator();
 
         SyntaxChecker check = check(eval, stx);
@@ -87,7 +88,14 @@ SyntaxValue expand(Expander expander, Environment env, SyntaxSexp stx)
         for (int i = 1; i < arity; i++)
         {
             SyntaxSymbol identifier = check.requiredIdentifier(i);
-            children[i] = expander.expandExpression(env, identifier);
+
+            // We don't want to expand the identifier since it might be syntax
+            // and that will fail. But we do want to determine its binding so
+            // we can look up documentation at runtime. This may resolve to a
+            // FreeBinding, which will trigger an unbound-identifier error
+            // during compilation, which is appropriate.
+
+            identifier.resolve();
         }
 
         return stx.copyReplacingChildren(eval, children);

runtime/src/test/fusion/scripts/bool.test.fusion

@@ -7,9 +7,13 @@
 // Here's the bindings we expect to be available:
 (module check_bindings '/fusion/bool'
   [
-    and, cond, if, is_bool,
+    // These syntax forms cannot be verified this way.
+    // https://github.com/ion-fusion/fusion-java/issues/122
+    // and, cond, if, or, unless, when
+
+    is_bool,
     is_false, is_true, is_truthy, is_untruthy,
-    not, or, unless, when,
+    not,
   ])
 
 

runtime/src/test/fusion/scripts/syntax.test.fusion

@@ -24,6 +24,10 @@
 (datum_to_syntax [id] id)
 
 
+// Syntax forms cannot be used as expressions
+(expect_syntax_error (list 1 if 2))
+
+
 //==========================================================================
 // is_identifier