Merge pull request #824 from kirbyfan64/short-circuit

Make and/or short-circuit

hy/compiler.py

@@ -1676,17 +1676,78 @@ class HyASTCompiler(object):
 
     @builds("and")
     @builds("or")
-    @checkargs(min=2)
     def compile_logical_or_and_and_operator(self, expression):
-        ops = {"and": ast.And,
-               "or": ast.Or}
+        ops = {"and": (ast.And, "True"),
+               "or": (ast.Or, "None")}
         operator = expression.pop(0)
-        values, ret, _ = self._compile_collect(expression)
+        opnode, default = ops[operator]
+        root_line, root_column = operator.start_line, operator.start_column
+        if len(expression) == 0:
+            return ast.Name(id=default,
+                            ctx=ast.Load(),
+                            lineno=root_line,
+                            col_offset=root_column)
+        elif len(expression) == 1:
+            return self.compile(expression[0])
+        ret = Result()
+        values = list(map(self.compile, expression))
+        has_stmt = any(value.stmts for value in values)
+        if has_stmt:
+            # Compile it to an if...else sequence
+            var = self.get_anon_var()
+            name = ast.Name(id=var,
+                            ctx=ast.Store(),
+                            lineno=root_line,
+                            col_offset=root_column)
+            expr_name = ast.Name(id=var,
+                                 ctx=ast.Load(),
+                                 lineno=root_line,
+                                 col_offset=root_column)
 
-        ret += ast.BoolOp(op=ops[operator](),
-                          lineno=operator.start_line,
-                          col_offset=operator.start_column,
-                          values=values)
+            def make_assign(value, node=None):
+                if node is None:
+                    line, column = root_line, root_column
+                else:
+                    line, column = node.lineno, node.col_offset
+                return ast.Assign(targets=[ast.Name(id=var,
+                                                    ctx=ast.Store(),
+                                                    lineno=line,
+                                                    col_offset=column)],
+                                  value=value,
+                                  lineno=line,
+                                  col_offset=column)
+            root = []
+            current = root
+            for i, value in enumerate(values):
+                if value.stmts:
+                    node = value.stmts[0]
+                    current.extend(value.stmts)
+                else:
+                    node = value.expr
+                current.append(make_assign(value.force_expr, value.force_expr))
+                if i == len(values)-1:
+                    # Skip a redundant 'if'.
+                    break
+                if operator == "and":
+                    cond = expr_name
+                elif operator == "or":
+                    cond = ast.UnaryOp(op=ast.Not(),
+                                       operand=expr_name,
+                                       lineno=node.lineno,
+                                       col_offset=node.col_offset)
+                current.append(ast.If(test=cond,
+                                      body=[],
+                                      lineno=node.lineno,
+                                      col_offset=node.col_offset,
+                                      orelse=[]))
+                current = current[-1].body
+            ret = sum(root, ret)
+            ret += Result(expr=expr_name, temp_variables=[expr_name, name])
+        else:
+            ret += ast.BoolOp(op=opnode(),
+                              lineno=root_line,
+                              col_offset=root_column,
+                              values=[value.force_expr for value in values])
         return ret
 
     @builds("=")

tests/native_tests/language.hy

@@ -782,19 +782,35 @@
 (defn test-and []
   "NATIVE: test the and function"
   (let [[and123 (and 1 2 3)]
-        [and-false (and 1 False 3)]]
+        [and-false (and 1 False 3)]
+        [and-true (and)]
+        [and-single (and 1)]]
     (assert (= and123 3))
-    (assert (= and-false False))))
+    (assert (= and-false False))
+    (assert (= and-true True))
+    (assert (= and-single 1)))
+  ; short circuiting
+  (setv a 1)
+  (and 0 (setv a 2))
+  (assert (= a 1)))
 
 
 (defn test-or []
   "NATIVE: test the or function"
   (let [[or-all-true (or 1 2 3 True "string")]
         [or-some-true (or False "hello")]
-        [or-none-true (or False False)]]
+        [or-none-true (or False False)]
+        [or-false (or)]
+        [or-single (or 1)]]
     (assert (= or-all-true 1))
     (assert (= or-some-true "hello"))
-    (assert (= or-none-true False))))
+    (assert (= or-none-true False))
+    (assert (= or-false nil))
+    (assert (= or-single 1)))
+  ; short circuiting
+  (setv a 1)
+  (or 1 (setv a 2))
+  (assert (= a 1)))
 
 
 (defn test-if-return-branching []