Raise exceptions when no handlers are provided.

Also small DRYing in try handling.

Previously, writing a bare (try (foo)) would invoke Pokemon
exception catching (gotta catch 'em all) instead of the correct
behavior, which is to raise the exception if no handler is provided.

Note that this is a cute feature of Hy, as a `try` with no `except`
is a syntax error.  We avoid the syntax error here because we don't
use Python's compiler, which is the only thing that can throw
Syntax Errors.  :D

Fixes #555.

AUTHORS

@@ -45,3 +45,4 @@
 * kirbyfan64 <kirbyfan64@users.noreply.github.com>
 * Brendan Curran-Johnson <brendan@bcjbcj.ca>
 * Ivan Kozik <ivan@ludios.org>
+* Allison Kaptur <allison.kaptur@gmail.com>

hy/compiler.py

@@ -732,25 +732,10 @@ def compile_try_expression(self, expr):
                 handler_results += self._compile_catch_expression(e, name)
                 handlers.append(handler_results.stmts.pop())
             elif e[0] == HySymbol("else"):
-                if orelse:
-                    raise HyTypeError(
-                        e,
-                        "`try' cannot have more than one `else'")
-                else:
-                    orelse = self._compile_branch(e[1:])
-                    # XXX tempvar magic
-                    orelse += orelse.expr_as_stmt()
-                    orelse = orelse.stmts
+                orelse = self.try_except_helper(e, HySymbol("else"), orelse)
             elif e[0] == HySymbol("finally"):
-                if finalbody:
-                    raise HyTypeError(
-                        e,
-                        "`try' cannot have more than one `finally'")
-                else:
-                    finalbody = self._compile_branch(e[1:])
-                    # XXX tempvar magic
-                    finalbody += finalbody.expr_as_stmt()
-                    finalbody = finalbody.stmts
+                finalbody = self.try_except_helper(e, HySymbol("finally"),
+                                                   finalbody)
             else:
                 raise HyTypeError(e, "Unknown expression in `try'")
 
@@ -768,8 +753,8 @@ def compile_try_expression(self, expr):
                 col_offset=expr.start_column,
                 type=None,
                 name=None,
-                body=[ast.Pass(lineno=expr.start_line,
-                               col_offset=expr.start_column)])]
+                body=[ast.Raise(lineno=expr.start_line,
+                                col_offset=expr.start_column)])]
 
         ret = handler_results
 
@@ -809,6 +794,17 @@ def compile_try_expression(self, expr):
             body=body,
             orelse=orelse) + returnable
 
+    def try_except_helper(self, hy_obj, symbol, accumulated):
+        if accumulated:
+            raise HyTypeError(
+                hy_obj,
+                "`try' cannot have more than one `%s'" % symbol)
+        else:
+            accumulated = self._compile_branch(hy_obj[1:])
+            accumulated += accumulated.expr_as_stmt()
+            accumulated = accumulated.stmts
+        return accumulated
+
     @builds("except")
     @builds("catch")
     def magic_internal_form(self, expr):

tests/native_tests/language.hy

@@ -236,6 +236,11 @@
   "NATIVE: test do"
   (do))
 
+(defn test-bare-try [] (try
+    (try (raise ValueError))
+  (except [ValueError])
+  (else (assert false))))
+
 
 (defn test-exceptions []
   "NATIVE: test Exceptions"