hy/hy/compiler.py

# -*- encoding: utf-8 -*-
#
# Copyright (c) 2013 Paul Tagliamonte <paultag@debian.org>
# Copyright (c) 2013 Julien Danjou <julien@danjou.info>
#
# Permission is hereby granted, free of charge, to any person obtaining a
# copy of this software and associated documentation files (the "Software"),
# to deal in the Software without restriction, including without limitation
# the rights to use, copy, modify, merge, publish, distribute, sublicense,
# and/or sell copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
# THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
# DEALINGS IN THE SOFTWARE.

from hy.errors import HyError

from hy.models.lambdalist import HyLambdaListKeyword
from hy.models.expression import HyExpression
from hy.models.keyword import HyKeyword
from hy.models.integer import HyInteger
from hy.models.complex import HyComplex
from hy.models.string import HyString
from hy.models.symbol import HySymbol
from hy.models.float import HyFloat
from hy.models.list import HyList
from hy.models.dict import HyDict

from hy.util import flatten_literal_list, str_type, temporary_attribute_value

from collections import defaultdict
import traceback
import codecs
import ast
import sys


class HyCompileError(HyError):
    def __init__(self, exception, traceback=None):
        self.exception = exception
        self.traceback = traceback

    def __str__(self):
        if isinstance(self.exception, HyTypeError):
            return str(self.exception)
        if self.traceback:
            tb = "".join(traceback.format_tb(self.traceback)).strip()
        else:
            tb = "No traceback available. 😟"
        return("Internal Compiler Bug 😱\n⤷ %s: %s\nCompilation traceback:\n%s"
               % (self.exception.__class__.__name__,
                  self.exception, tb))


class HyTypeError(TypeError):
    def __init__(self, expression, message):
        super(HyTypeError, self).__init__(message)
        self.expression = expression

    def __str__(self):
        return (super(HyTypeError, self).__str__() + " (line %s, column %d)"
                % (self.expression.start_line,
                   self.expression.start_column))

_compile_table = {}


def ast_str(foobar):
    if sys.version_info[0] >= 3:
        return str(foobar)

    try:
        return str(foobar)
    except UnicodeEncodeError:
        pass

    enc = codecs.getencoder('punycode')
    foobar, _ = enc(foobar)
    return "hy_%s" % (str(foobar).replace("-", "_"))


def builds(_type):
    def _dec(fn):
        _compile_table[_type] = fn
        return fn
    return _dec


def _raise_wrong_args_number(expression, error):
    raise HyTypeError(expression,
                      error % (expression.pop(0),
                               len(expression)))


def checkargs(exact=None, min=None, max=None):
    def _dec(fn):
        def checker(self, expression):
            if exact is not None and (len(expression) - 1) != exact:
                _raise_wrong_args_number(
                    expression, "`%%s' needs %d arguments, got %%d" % exact)

            if min is not None and (len(expression) - 1) < min:
                _raise_wrong_args_number(
                    expression,
                    "`%%s' needs at least %d arguments, got %%d" % (min))

            if max is not None and (len(expression) - 1) > max:
                _raise_wrong_args_number(
                    expression,
                    "`%%s' needs at most %d arguments, got %%d" % (max))

            return fn(self, expression)

        return checker
    return _dec


class HyASTCompiler(object):

    def __init__(self):
        self.returnable = False
        self.anon_fn_count = 0
        self.imports = defaultdict(list)

    def is_returnable(self, v):
        return temporary_attribute_value(self, "returnable", v)

    def compile(self, tree):
        try:
            _type = type(tree)
            if _type in _compile_table:
                return _compile_table[_type](self, tree)
        except HyCompileError:
            # compile calls compile, so we're going to have multiple raise
            # nested; so let's re-raise this exception, let's not wrap it in
            # another HyCompileError!
            raise
        except Exception as e:
            raise HyCompileError(e, sys.exc_info()[2])

        raise HyCompileError(
            Exception("Unknown type: `%s'" % (str(type(tree)))))

    def _mangle_branch(self, tree, start_line, start_column):
        tree = list(flatten_literal_list(tree))
        tree = list(filter(bool, tree))  # Remove empty statements

        # If tree is empty, just return a pass statement
        if tree == []:
            return [ast.Pass(lineno=start_line, col_offset=start_column)]

        tree.reverse()

        ret = []

        if self.returnable:
            el = tree[0]
            if not isinstance(el, ast.stmt):
                el = tree.pop(0)
                ret.append(ast.Return(value=el,
                                      lineno=el.lineno,
                                      col_offset=el.col_offset))
            if isinstance(el, ast.FunctionDef):
                ret.append(ast.Return(
                    value=ast.Name(
                        arg=el.name, id=el.name, ctx=ast.Load(),
                        lineno=el.lineno, col_offset=el.col_offset),
                    lineno=el.lineno, col_offset=el.col_offset))

        for el in tree:
            if isinstance(el, ast.stmt):
                ret.append(el)
                continue

            ret.append(ast.Expr(
                value=el,
                lineno=el.lineno,
                col_offset=el.col_offset))

        ret.reverse()
        return ret

    def _parse_lambda_list(self, exprs):
        """ Return FunctionDef parameter values from lambda list."""
        args = []
        defaults = []
        varargs = None
        kwargs = None
        lambda_keyword = None

        for expr in exprs:

            if isinstance(expr, HyLambdaListKeyword):
                if expr not in expr._valid_types:
                    raise HyCompileError("{0} is not a valid "
                                         "lambda-keyword.".format(repr(expr)))
                if expr == "&rest" and lambda_keyword is None:
                    lambda_keyword = expr
                elif expr == "&optional":
                    lambda_keyword = expr
                elif expr == "&key":
                    lambda_keyword = expr
                elif expr == "&kwargs":
                    lambda_keyword = expr
                else:
                    raise HyCompileError("{0} is in an invalid "
                                         "position.".format(repr(expr)))
                # we don't actually care about this token, so we set
                # our state and continue to the next token...
                continue

            if lambda_keyword is None:
                args.append(expr)
            elif lambda_keyword == "&rest":
                if varargs:
                    raise HyCompileError("There can only be one "
                                         "&rest argument")
                varargs = str(expr)
            elif lambda_keyword == "&key":
                if type(expr) != HyDict:
                    raise TypeError("There can only be one &key "
                                    "argument")
                else:
                    if len(defaults) > 0:
                        raise HyCompileError("There can only be "
                                             "one &key argument")
                    # As you can see, Python has a funny way of
                    # defining keyword arguments.
                    for k, v in expr.items():
                        args.append(k)
                        defaults.append(self.compile(v))
            elif lambda_keyword == "&optional":
                # not implemented yet.
                pass
            elif lambda_keyword == "&kwargs":
                if kwargs:
                    raise HyCompileError("There can only be one "
                                         "&kwargs argument")
                kwargs = str(expr)

        return args, defaults, varargs, kwargs

    @builds(list)
    def compile_raw_list(self, entries):
        return [self.compile(x) for x in entries]

    def _render_quoted_form(self, form):
        name = form.__class__.__name__
        self.imports["hy"].append((name, form))

        if isinstance(form, HyList):
            return HyExpression(
                [HySymbol(name),
                 HyList([self._render_quoted_form(x) for x in form])]
            ).replace(form)
        elif isinstance(form, HySymbol):
            return HyExpression([HySymbol(name), HyString(form)]).replace(form)
        return HyExpression([HySymbol(name), form]).replace(form)

    @builds("quote")
    @checkargs(exact=1)
    def compile_quote(self, entries):
        return self.compile(self._render_quoted_form(entries[1]))

    @builds("eval")
    @checkargs(exact=1)
    def compile_eval(self, expr):
        expr.pop(0)
        self.imports["hy.importer"].append(("hy_eval", expr))

        return self.compile(HyExpression([
            HySymbol("hy_eval")] + expr + [
                HyExpression([HySymbol("locals")])]).replace(expr))

    @builds("do")
    @builds("progn")
    def compile_do_expression(self, expr):
        return [self.compile(x) for x in expr[1:]]

    @builds("throw")
    @builds("raise")
    @checkargs(max=1)
    def compile_throw_expression(self, expr):
        expr.pop(0)
        exc = self.compile(expr.pop(0)) if expr else None
        return ast.Raise(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            type=exc,
            exc=exc,
            inst=None,
            tback=None)

    @builds("try")
    def compile_try_expression(self, expr):
        expr.pop(0)  # try

        try:
            body = expr.pop(0)
        except IndexError:
            body = []

        # (try something…)
        body = self._code_branch(self.compile(body),
                                 expr.start_line,
                                 expr.start_column)

        orelse = []
        finalbody = []
        handlers = []

        for e in expr:
            if not len(e):
                raise HyTypeError(e, "Empty list not allowed in `try'")

            if e[0] in (HySymbol("except"), HySymbol("catch")):
                handlers.append(self.compile(e))
            elif e[0] == HySymbol("else"):
                if orelse:
                    raise HyTypeError(
                        e,
                        "`try' cannot have more than one `else'")
                else:
                    orelse = self._code_branch(self.compile(e[1:]),
                                               e.start_line,
                                               e.start_column)
            elif e[0] == HySymbol("finally"):
                if finalbody:
                    raise HyTypeError(
                        e,
                        "`try' cannot have more than one `finally'")
                else:
                    finalbody = self._code_branch(self.compile(e[1:]),
                                                  e.start_line,
                                                  e.start_column)
            else:
                raise HyTypeError(e, "Unknown expression in `try'")

        # Using (else) without (except) is verboten!
        if orelse and not handlers:
            raise HyTypeError(
                e,
                "`try' cannot have `else' without `except'")

        # (try) or (try BODY)
        # Generate a default handler for Python >= 3.3 and pypy
        if not handlers and not finalbody and not orelse:
            handlers = [ast.ExceptHandler(
                lineno=expr.start_line,
                col_offset=expr.start_column,
                type=None,
                name=None,
                body=[ast.Pass(lineno=expr.start_line,
                               col_offset=expr.start_column)])]

        if sys.version_info[0] >= 3 and sys.version_info[1] >= 3:
            # Python 3.3 features a merge of TryExcept+TryFinally into Try.
            return ast.Try(
                lineno=expr.start_line,
                col_offset=expr.start_column,
                body=body,
                handlers=handlers,
                orelse=orelse,
                finalbody=finalbody)

        if finalbody:
            if handlers:
                return ast.TryFinally(
                    lineno=expr.start_line,
                    col_offset=expr.start_column,
                    body=[ast.TryExcept(
                        lineno=expr.start_line,
                        col_offset=expr.start_column,
                        handlers=handlers,
                        body=body,
                        orelse=orelse)],
                    finalbody=finalbody)

            return ast.TryFinally(
                lineno=expr.start_line,
                col_offset=expr.start_column,
                body=body,
                finalbody=finalbody)

        return ast.TryExcept(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            handlers=handlers,
            body=body,
            orelse=orelse)

    @builds("catch")
    @builds("except")
    def compile_catch_expression(self, expr):
        catch = expr.pop(0)  # catch

        try:
            exceptions = expr.pop(0)
        except IndexError:
            exceptions = HyList()
        # exceptions catch should be either:
        # [[list of exceptions]]
        # or
        # [variable [list of exceptions]]
        # or
        # [variable exception]
        # or
        # [exception]
        # or
        # []
        if not isinstance(exceptions, HyList):
            raise HyTypeError(exceptions,
                              "`%s' exceptions list is not a list" % catch)
        if len(exceptions) > 2:
            raise HyTypeError(exceptions,
                              "`%s' exceptions list is too long" % catch)

        # [variable [list of exceptions]]
        # let's pop variable and use it as name
        if len(exceptions) == 2:
            name = exceptions.pop(0)
            if sys.version_info[0] >= 3:
                # Python3 features a change where the Exception handler
                # moved the name from a Name() to a pure Python String type.
                #
                # We'll just make sure it's a pure "string", and let it work
                # it's magic.
                name = ast_str(name)
            else:
                # Python2 requires an ast.Name, set to ctx Store.
                name = self._storeize(self.compile(name))
        else:
            name = None

        try:
            exceptions_list = exceptions.pop(0)
        except IndexError:
            exceptions_list = []

        if isinstance(exceptions_list, list):
            if len(exceptions_list):
                # [FooBar BarFoo] → catch Foobar and BarFoo exceptions
                _type = ast.Tuple(elts=[self.compile(x)
                                        for x in exceptions_list],
                                  lineno=expr.start_line,
                                  col_offset=expr.start_column,
                                  ctx=ast.Load())
            else:
                # [] → all exceptions catched
                _type = None
        elif isinstance(exceptions_list, HySymbol):
            _type = self.compile(exceptions_list)
        else:
            raise HyTypeError(exceptions,
                              "`%s' needs a valid exception list" % catch)

        body = self._code_branch([self.compile(x) for x in expr],
                                 expr.start_line,
                                 expr.start_column)

        return ast.ExceptHandler(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            type=_type,
            name=name,
            body=body)

    def _code_branch(self, branch, start_line, start_column):
        return self._mangle_branch((branch
                                    if isinstance(branch, list)
                                    else [branch]),
                                   start_line,
                                   start_column)

    @builds("if")
    @checkargs(min=2, max=3)
    def compile_if_expression(self, expr):
        expr.pop(0)             # if
        test = self.compile(expr.pop(0))
        body = self._code_branch(self.compile(expr.pop(0)),
                                 expr.start_line,
                                 expr.start_column)

        if len(expr) == 1:
            orel = self._code_branch(self.compile(expr.pop(0)),
                                     expr.start_line,
                                     expr.start_column)
        else:
            orel = []

        return ast.If(test=test,
                      body=body,
                      orelse=orel,
                      lineno=expr.start_line,
                      col_offset=expr.start_column)

    @builds("print")
    def compile_print_expression(self, expr):
        call = expr.pop(0)  # print
        if sys.version_info[0] >= 3:
            call = self.compile(call)
            # AST changed with Python 3, we now just call it.
            return ast.Call(
                keywords=[],
                func=call,
                args=[self.compile(x) for x in expr],
                lineno=expr.start_line,
                col_offset=expr.start_column)

        return ast.Print(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            dest=None,
            values=[self.compile(x) for x in expr],
            nl=True)

    @builds("assert")
    @checkargs(1)
    def compile_assert_expression(self, expr):
        expr.pop(0)  # assert
        e = expr.pop(0)
        return ast.Assert(test=self.compile(e),
                          msg=None,
                          lineno=e.start_line,
                          col_offset=e.start_column)

    @builds("global")
    @checkargs(1)
    def compile_global_expression(self, expr):
        expr.pop(0)  # global
        e = expr.pop(0)
        return ast.Global(names=[ast_str(e)],
                          lineno=e.start_line,
                          col_offset=e.start_column)

    @builds("lambda")
    @checkargs(min=2)
    def compile_lambda_expression(self, expr):
        expr.pop(0)
        sig = expr.pop(0)
        body = expr.pop(0)
        # assert expr is empty
        return ast.Lambda(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            args=ast.arguments(args=[
                ast.Name(arg=ast_str(x), id=ast_str(x),
                         ctx=ast.Param(),
                         lineno=x.start_line,
                         col_offset=x.start_column)
                for x in sig],
                vararg=None,
                kwarg=None,
                defaults=[],
                kwonlyargs=[],
                kw_defaults=[]),
            body=self.compile(body))

    @builds("yield")
    @checkargs(max=1)
    def compile_yield_expression(self, expr):
        expr.pop(0)
        value = None
        if expr != []:
            value = self.compile(expr.pop(0))
        return ast.Yield(
            value=value,
            lineno=expr.start_line,
            col_offset=expr.start_column)

    @builds("import")
    def compile_import_expression(self, expr):
        def _compile_import(expr, module, names=None, importer=ast.Import):
            return [
                importer(
                    lineno=expr.start_line,
                    col_offset=expr.start_column,
                    module=ast_str(module),
                    names=names or [
                        ast.alias(name=ast_str(module), asname=None)
                    ],
                    level=0)
            ]

        expr.pop(0)  # index
        rimports = []
        while len(expr) > 0:
            iexpr = expr.pop(0)

            if isinstance(iexpr, HySymbol):
                rimports += _compile_import(expr, iexpr)
                continue

            if isinstance(iexpr, HyList) and len(iexpr) == 1:
                rimports += _compile_import(expr, iexpr.pop(0))
                continue

            if isinstance(iexpr, HyList) and iexpr:
                module = iexpr.pop(0)
                entry = iexpr[0]
                if isinstance(entry, HyKeyword) and entry == HyKeyword(":as"):
                    assert len(iexpr) == 2, "garbage after aliased import"
                    iexpr.pop(0)  # :as
                    alias = iexpr.pop(0)
                    rimports += _compile_import(
                        expr,
                        ast_str(module),
                        [
                            ast.alias(name=ast_str(module),
                                      asname=ast_str(alias))
                        ]
                    )
                    continue

                if isinstance(entry, HyList):
                    names = []
                    while entry:
                        sym = entry.pop(0)
                        if entry and isinstance(entry[0], HyKeyword):
                            entry.pop(0)
                            alias = ast_str(entry.pop(0))
                        else:
                            alias = None
                        names += [
                            ast.alias(name=ast_str(sym),
                                      asname=alias)
                        ]

                    rimports += _compile_import(expr, module,
                                                names, ast.ImportFrom)
                    continue

                raise TypeError("Unknown entry (`%s`) in the HyList" % (entry))

        if len(rimports) == 1:
            return rimports[0]
        else:
            return rimports

    @builds("get")
    @checkargs(2)
    def compile_index_expression(self, expr):
        expr.pop(0)  # index
        val = self.compile(expr.pop(0))  # target
        sli = self.compile(expr.pop(0))  # slice

        return ast.Subscript(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            value=val,
            slice=ast.Index(value=sli),
            ctx=ast.Load())

    @builds("slice")
    @checkargs(min=1, max=3)
    def compile_slice_expression(self, expr):
        expr.pop(0)  # index
        val = self.compile(expr.pop(0))  # target

        low = None
        if expr != []:
            low = self.compile(expr.pop(0))

        high = None
        if expr != []:
            high = self.compile(expr.pop(0))

        return ast.Subscript(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            value=val,
            slice=ast.Slice(lower=low,
                            upper=high,
                            step=None),
            ctx=ast.Load())

    @builds("assoc")
    @checkargs(3)
    def compile_assoc_expression(self, expr):
        expr.pop(0)  # assoc
        # (assoc foo bar baz)  => foo[bar] = baz
        target = expr.pop(0)
        key = expr.pop(0)
        val = expr.pop(0)

        return ast.Assign(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            targets=[
                ast.Subscript(
                    lineno=expr.start_line,
                    col_offset=expr.start_column,
                    value=self.compile(target),
                    slice=ast.Index(value=self.compile(key)),
                    ctx=ast.Store())],
            value=self.compile(val))

    @builds("decorate_with")
    @checkargs(min=1)
    def compile_decorate_expression(self, expr):
        expr.pop(0)  # decorate-with
        fn = self.compile(expr.pop(-1))
        if type(fn) != ast.FunctionDef:
            raise HyTypeError(expr, "Decorated a non-function")
        fn.decorator_list = [self.compile(x) for x in expr]
        return fn

    @builds("with")
    @checkargs(min=2)
    def compile_with_expression(self, expr):
        expr.pop(0)  # with

        args = expr.pop(0)
        if len(args) > 2 or len(args) < 1:
            raise HyTypeError(expr, "with needs [arg (expr)] or [(expr)]")

        args.reverse()
        ctx = self.compile(args.pop(0))

        thing = None
        if args != []:
            thing = self._storeize(self.compile(args.pop(0)))

        ret = ast.With(context_expr=ctx,
                       lineno=expr.start_line,
                       col_offset=expr.start_column,
                       optional_vars=thing,
                       body=self._code_branch(
                           [self.compile(x) for x in expr],
                           expr.start_line,
                           expr.start_column))

        if sys.version_info[0] >= 3 and sys.version_info[1] >= 3:
            ret.items = [ast.withitem(context_expr=ctx, optional_vars=thing)]

        return ret

    @builds(",")
    def compile_tuple(self, expr):
        expr.pop(0)
        return ast.Tuple(elts=[self.compile(x) for x in expr],
                         lineno=expr.start_line,
                         col_offset=expr.start_column,
                         ctx=ast.Load())

    @builds("list_comp")
    @checkargs(min=2, max=3)
    def compile_list_comprehension(self, expr):
        # (list-comp expr (target iter) cond?)
        expr.pop(0)
        expression = expr.pop(0)
        tar_it = iter(expr.pop(0))
        targets = zip(tar_it, tar_it)

        cond = self.compile(expr.pop(0)) if expr != [] else None

        ret = ast.ListComp(
            lineno=expr.start_line,
            col_offset=expr.start_column,
            elt=self.compile(expression),
            generators=[])

        for target, iterable in targets:
            ret.generators.append(ast.comprehension(
                target=self._storeize(self.compile(target)),
                iter=self.compile(iterable),
                ifs=[]))

        if cond:
            ret.generators[-1].ifs.append(cond)

        return ret

    def _storeize(self, name):
        if isinstance(name, ast.Tuple):
            for x in name.elts:
                x.ctx = ast.Store()
        name.ctx = ast.Store()
        return name

    @builds("kwapply")
    @checkargs(2)
    def compile_kwapply_expression(self, expr):
        expr.pop(0)  # kwapply
        call = self.compile(expr.pop(0))
        kwargs = expr.pop(0)

        if type(call) != ast.Call:
            raise HyTypeError(expr, "kwapplying a non-call")

        if type(kwargs) != HyDict:
            raise TypeError("kwapplying with a non-dict")

        call.keywords = [ast.keyword(arg=ast_str(x),
                         value=self.compile(kwargs[x])) for x in kwargs]

        return call

    @builds("not")
    @builds("~")
    @checkargs(1)
    def compile_unary_operator(self, expression):
        ops = {"not": ast.Not,
               "~": ast.Invert}
        operator = expression.pop(0)
        operand = expression.pop(0)
        return ast.UnaryOp(op=ops[operator](),
                           operand=self.compile(operand),
                           lineno=operator.start_line,
                           col_offset=operator.start_column)

    @builds("and")
    @builds("or")
    @checkargs(min=2)
    def compile_logical_or_and_and_operator(self, expression):
        ops = {"and": ast.And,
               "or": ast.Or}
        operator = expression.pop(0)
        values = []
        for child in expression:
            values.append(self.compile(child))
        return ast.BoolOp(op=ops[operator](),
                          lineno=operator.start_line,
                          col_offset=operator.start_column,
                          values=values)

    @builds("=")
    @builds("!=")
    @builds("<")
    @builds("<=")
    @builds(">")
    @builds(">=")
    @builds("is")
    @builds("in")
    @builds("is_not")
    @builds("not_in")
    @checkargs(min=2)
    def compile_compare_op_expression(self, expression):
        ops = {"=": ast.Eq, "!=": ast.NotEq,
               "<": ast.Lt, "<=": ast.LtE,
               ">": ast.Gt, ">=": ast.GtE,
               "is": ast.Is, "is_not": ast.IsNot,
               "in": ast.In, "not_in": ast.NotIn}

        inv = expression.pop(0)
        op = ops[inv]
        ops = [op() for x in range(1, len(expression))]
        e = expression.pop(0)

        return ast.Compare(left=self.compile(e),
                           ops=ops,
                           comparators=[self.compile(x) for x in expression],
                           lineno=e.start_line,
                           col_offset=e.start_column)

    @builds("+")
    @builds("%")
    @builds("/")
    @builds("//")
    @builds("*")
    @builds("**")
    @builds("<<")
    @builds(">>")
    @builds("|")
    @builds("^")
    @builds("&")
    @checkargs(min=2)
    def compile_maths_expression(self, expression):
        ops = {"+": ast.Add,
               "/": ast.Div,
               "//": ast.FloorDiv,
               "*": ast.Mult,
               "-": ast.Sub,
               "%": ast.Mod,
               "**": ast.Pow,
               "<<": ast.LShift,
               ">>": ast.RShift,
               "|": ast.BitOr,
               "^": ast.BitXor,
               "&": ast.BitAnd}

        inv = expression.pop(0)
        op = ops[inv]

        left = self.compile(expression.pop(0))
        calc = None
        for child in expression:
            calc = ast.BinOp(left=left,
                             op=op(),
                             right=self.compile(child),
                             lineno=child.start_line,
                             col_offset=child.start_column)
            left = calc
        return calc

    @builds("-")
    @checkargs(min=1)
    def compile_maths_expression_sub(self, expression):
        if len(expression) > 2:
            return self.compile_maths_expression(expression)
        else:
            arg = expression[1]
            return ast.UnaryOp(op=ast.USub(),
                               operand=self.compile(arg),
                               lineno=arg.start_line,
                               col_offset=arg.start_column)

    @builds("+=")
    @builds("/=")
    @builds("//=")
    @builds("*=")
    @builds("_=")
    @builds("%=")
    @builds("**=")
    @builds("<<=")
    @builds(">>=")
    @builds("|=")
    @builds("^=")
    @builds("&=")
    @checkargs(2)
    def compile_augassign_expression(self, expression):
        ops = {"+=": ast.Add,
               "/=": ast.Div,
               "//=": ast.FloorDiv,
               "*=": ast.Mult,
               "_=": ast.Sub,
               "%=": ast.Mod,
               "**=": ast.Pow,
               "<<=": ast.LShift,
               ">>=": ast.RShift,
               "|=": ast.BitOr,
               "^=": ast.BitXor,
               "&=": ast.BitAnd}

        op = ops[expression[0]]

        target = self._storeize(self.compile(expression[1]))
        value = self.compile(expression[2])

        return ast.AugAssign(
            target=target,
            value=value,
            op=op(),
            lineno=expression.start_line,
            col_offset=expression.start_column)

    def compile_dotted_expression(self, expr):
        ofn = expr.pop(0)  # .join

        fn = HySymbol(ofn[1:])
        fn.replace(ofn)

        obj = expr.pop(0)  # [1 2 3 4]

        return ast.Call(
            func=ast.Attribute(
                lineno=expr.start_line,
                col_offset=expr.start_column,
                value=self.compile(obj),
                attr=ast_str(fn),
                ctx=ast.Load()),
            args=[self.compile(x) for x in expr],
            keywords=[],
            lineno=expr.start_line,
            col_offset=expr.start_column,
            starargs=None,
            kwargs=None)

    @builds(HyExpression)
    def compile_expression(self, expression):
        fn = expression[0]
        if isinstance(fn, HyString):
            if fn in _compile_table:
                return _compile_table[fn](self, expression)

            if expression[0].startswith("."):
                return self.compile_dotted_expression(expression)
        if isinstance(fn, HyKeyword):
            new_expr = HyExpression(["get", expression[1], fn])
            new_expr.start_line = expression.start_line
            new_expr.start_column = expression.start_column
            return self.compile_index_expression(new_expr)

        return ast.Call(func=self.compile(fn),
                        args=[self.compile(x) for x in expression[1:]],
                        keywords=[],
                        starargs=None,
                        kwargs=None,
                        lineno=expression.start_line,
                        col_offset=expression.start_column)

    @builds("def")
    @builds("setf")
    @builds("setv")
    @checkargs(2)
    def compile_def_expression(self, expression):
        expression.pop(0)  # "def"
        name = expression.pop(0)

        what = self.compile(expression.pop(0))

        if type(what) == ast.FunctionDef:
            # We special case a FunctionDef, since we can define by setting
            # FunctionDef's .name attribute, rather then foo == anon_fn. This
            # helps keep things clean.
            what.name = ast_str(name)
            return what

        name = self._storeize(self.compile(name))

        return ast.Assign(
            lineno=expression.start_line,
            col_offset=expression.start_column,
            targets=[name], value=what)

    @builds("foreach")
    @checkargs(min=1)
    def compile_for_expression(self, expression):
        with self.is_returnable(False):
            expression.pop(0)  # for
            name, iterable = expression.pop(0)
            target = self._storeize(self.compile_symbol(name))

            orelse = []
            # (foreach [] body (else …))
            if expression and expression[-1][0] == HySymbol("else"):
                else_expr = expression.pop()
                if len(else_expr) > 2:
                    raise HyTypeError(
                        else_expr,
                        "`else' statement in `foreach' is too long")
                elif len(else_expr) == 2:
                    orelse = self._code_branch(
                        self.compile(else_expr[1]),
                        else_expr[1].start_line,
                        else_expr[1].start_column)

            ret = ast.For(lineno=expression.start_line,
                          col_offset=expression.start_column,
                          target=target,
                          iter=self.compile(iterable),
                          body=self._code_branch(
                              [self.compile(x) for x in expression],
                              expression.start_line,
                              expression.start_column),
                          orelse=orelse)

        return ret

    @builds("while")
    @checkargs(min=2)
    def compile_while_expression(self, expr):
        expr.pop(0)  # "while"
        test = self.compile(expr.pop(0))

        return ast.While(test=test,
                         body=self._code_branch(
                             [self.compile(x) for x in expr],
                             expr.start_line,
                             expr.start_column),
                         orelse=[],
                         lineno=expr.start_line,
                         col_offset=expr.start_column)

    @builds(HyList)
    def compile_list(self, expr):
        return ast.List(
            elts=[self.compile(x) for x in expr],
            ctx=ast.Load(),
            lineno=expr.start_line,
            col_offset=expr.start_column)

    @builds("fn")
    @checkargs(min=1)
    def compile_fn_expression(self, expression):
        expression.pop(0)  # fn

        self.anon_fn_count += 1
        name = "_hy_anon_fn_%d" % (self.anon_fn_count)
        sig = expression.pop(0)

        body = []
        if expression != []:
            with self.is_returnable(True):
                tailop = self.compile(expression.pop(-1))
            with self.is_returnable(False):
                for el in expression:
                    body.append(self.compile(el))
            body.append(tailop)

        with self.is_returnable(True):
            body = self._code_branch(body,
                                     expression.start_line,
                                     expression.start_column)

            args, defaults, stararg, kwargs = self._parse_lambda_list(sig)

            ret = ast.FunctionDef(
                name=name,
                lineno=expression.start_line,
                col_offset=expression.start_column,
                args=ast.arguments(
                    args=[
                        ast.Name(
                            arg=ast_str(x), id=ast_str(x),
                            ctx=ast.Param(),
                            lineno=x.start_line,
                            col_offset=x.start_column)
                        for x in args],
                    vararg=stararg,
                    kwarg=kwargs,
                    kwonlyargs=[],
                    kw_defaults=[],
                    defaults=defaults),
                body=body,
                decorator_list=[])

        return ret

    @builds(HyInteger)
    def compile_integer(self, number):
        return ast.Num(n=int(number),
                       lineno=number.start_line,
                       col_offset=number.start_column)

    @builds(HyFloat)
    def compile_float(self, number):
        return ast.Num(n=float(number),
                       lineno=number.start_line,
                       col_offset=number.start_column)

    @builds(HyComplex)
    def compile_complex(self, number):
        return ast.Num(n=complex(number),
                       lineno=number.start_line,
                       col_offset=number.start_column)

    @builds(HySymbol)
    def compile_symbol(self, symbol):
        if "." in symbol:
            glob, local = symbol.rsplit(".", 1)
            glob = HySymbol(glob)
            glob.replace(symbol)

            return ast.Attribute(
                lineno=symbol.start_line,
                col_offset=symbol.start_column,
                value=self.compile_symbol(glob),
                attr=ast_str(local),
                ctx=ast.Load()
            )

        return ast.Name(id=ast_str(symbol),
                        arg=ast_str(symbol),
                        ctx=ast.Load(),
                        lineno=symbol.start_line,
                        col_offset=symbol.start_column)

    @builds(HyString)
    def compile_string(self, string):
        return ast.Str(s=str_type(string), lineno=string.start_line,
                       col_offset=string.start_column)

    @builds(HyKeyword)
    def compile_keyword(self, keyword):
        return ast.Str(s=str_type(keyword), lineno=keyword.start_line,
                       col_offset=keyword.start_column)

    @builds(HyDict)
    def compile_dict(self, m):
        keys = []
        vals = []
        for entry in m:
            keys.append(self.compile(entry))
            vals.append(self.compile(m[entry]))

        return ast.Dict(
            lineno=m.start_line,
            col_offset=m.start_column,
            keys=keys,
            values=vals)


def hy_compile(tree, root=None):
    " Compile a HyObject tree into a Python AST tree. "
    compiler = HyASTCompiler()
    tlo = root
    if root is None:
        tlo = ast.Module

    _ast = compiler.compile(tree)
    if type(_ast) == list:
        _ast = compiler._mangle_branch(_ast, 0, 0)

        if hasattr(sys, "subversion"):
            implementation = sys.subversion[0].lower()
        elif hasattr(sys, "implementation"):
            implementation = sys.implementation.name.lower()

        imports = []
        for package in compiler.imports:
            imported = set()
            syms = compiler.imports[package]
            for entry, form in syms:
                if entry in imported:
                    continue

                replace = form
                if implementation != "cpython":
                    # using form causes pypy to blow up; let's conditionally
                    # add this for cpython, since it won't go through and make
                    # sure the AST makes sense. Muhahaha. - PRT
                    replace = tree[0]

                imported.add(entry)
                imports.append(HyExpression([
                    HySymbol("import"),
                    HyList([HySymbol(package), HyList([HySymbol(entry)])])
                ]).replace(replace))

        _ast = compiler.compile(imports) + _ast

    ret = tlo(body=_ast)
    return ret