Move logic from macroexpand_1 to macroexpand

By ending macro-expansion immediately when appropriate, this change fixes a bug arising from the fact that NaN != NaN.

NEWS.rst

@@ -42,6 +42,7 @@ Bug Fixes
 * Fixed a case where `->` and `->>` duplicated an argument
 * Fixed bugs that caused `defclass` to drop statements or crash
 * Fixed a REPL crash caused by illegle unicode escape string inputs
+* `NaN` can no longer create an infinite loop during macro-expansion
 
 Misc. Improvements
 ----------------------------

hy/macros.py

@@ -156,58 +156,59 @@ def make_empty_fn_copy(fn):
     return empty_fn
 
 
-def macroexpand(tree, compiler):
+def macroexpand(tree, compiler, once=False):
     """Expand the toplevel macros for the `tree`.
 
     Load the macros from the given `module_name`, then expand the (top-level)
-    macros in `tree` until it stops changing.
+    macros in `tree` until we no longer can.
 
     """
     load_macros(compiler.module_name)
-    old = None
-    while old != tree:
-        old = tree
-        tree = macroexpand_1(tree, compiler)
-    return tree
+    while True:
+
+        if not isinstance(tree, HyExpression) or tree == []:
+            return tree
+
+        fn = tree[0]
+        if fn in ("quote", "quasiquote") or not isinstance(fn, HySymbol):
+            return tree
+
+        fn = mangle(fn)
+        m = _hy_macros[compiler.module_name].get(fn) or _hy_macros[None].get(fn)
+        if not m:
+            return tree
+
+        opts = {}
+        if m._hy_macro_pass_compiler:
+            opts['compiler'] = compiler
+
+        try:
+            m_copy = make_empty_fn_copy(m)
+            m_copy(compiler.module_name, *tree[1:], **opts)
+        except TypeError as e:
+            msg = "expanding `" + str(tree[0]) + "': "
+            msg += str(e).replace("<lambda>()", "", 1).strip()
+            raise HyMacroExpansionError(tree, msg)
+
+        try:
+            obj = m(compiler.module_name, *tree[1:], **opts)
+        except HyTypeError as e:
+            if e.expression is None:
+                e.expression = tree
+            raise
+        except Exception as e:
+            msg = "expanding `" + str(tree[0]) + "': " + repr(e)
+            raise HyMacroExpansionError(tree, msg)
+        tree = replace_hy_obj(obj, tree)
+
+        if once:
+            return tree
 
 
 def macroexpand_1(tree, compiler):
     """Expand the toplevel macro from `tree` once, in the context of
-    `module_name`."""
-    if not isinstance(tree, HyExpression) or tree == []:
-        return tree
-
-    fn = tree[0]
-    if fn in ("quote", "quasiquote") or not isinstance(fn, HySymbol):
-        return tree
-
-    fn = mangle(fn)
-    m = _hy_macros[compiler.module_name].get(fn) or _hy_macros[None].get(fn)
-    if not m:
-        return tree
-
-    opts = {}
-    if m._hy_macro_pass_compiler:
-        opts['compiler'] = compiler
-
-    try:
-        m_copy = make_empty_fn_copy(m)
-        m_copy(compiler.module_name, *tree[1:], **opts)
-    except TypeError as e:
-        msg = "expanding `" + str(tree[0]) + "': "
-        msg += str(e).replace("<lambda>()", "", 1).strip()
-        raise HyMacroExpansionError(tree, msg)
-
-    try:
-        obj = m(compiler.module_name, *tree[1:], **opts)
-    except HyTypeError as e:
-        if e.expression is None:
-            e.expression = tree
-        raise
-    except Exception as e:
-        msg = "expanding `" + str(tree[0]) + "': " + repr(e)
-        raise HyMacroExpansionError(tree, msg)
-    return replace_hy_obj(obj, tree)
+    `compiler`."""
+    return macroexpand(tree, compiler, once=True)
 
 
 def tag_macroexpand(tag, tree, compiler):

tests/macros/test_macro_processor.py

@@ -5,7 +5,7 @@
 from hy.macros import macro, macroexpand
 from hy.lex import tokenize
 
-from hy.models import HyString, HyList, HySymbol, HyExpression
+from hy.models import HyString, HyList, HySymbol, HyExpression, HyFloat
 from hy.errors import HyMacroExpansionError
 
 from hy.compiler import HyASTCompiler
@@ -53,3 +53,12 @@ def test_preprocessor_exceptions():
     except HyMacroExpansionError as e:
         assert "_hy_anon_fn_" not in str(e)
         assert "TypeError" not in str(e)
+
+
+def test_macroexpand_nan():
+   # https://github.com/hylang/hy/issues/1574
+   import math
+   NaN = float('nan')
+   x = macroexpand(HyFloat(NaN), HyASTCompiler(__name__))
+   assert type(x) is HyFloat
+   assert math.isnan(x)