gitmirror/lark/visitors.py

from functools import wraps

from .utils import smart_decorator
from .tree import Tree
from .exceptions import VisitError, GrammarError
from .lexer import Token

###{standalone
from inspect import getmembers, getmro

class Discard(Exception):
    pass

# Transformers

class Transformer:
    """Visits the tree recursively, starting with the leaves and finally the root (bottom-up)

    Calls its methods (provided by user via inheritance) according to tree.data
    The returned value replaces the old one in the structure.

    Can be used to implement map or reduce.
    """

    __visit_tokens__ = False   # For backwards compatibility
    def __init__(self,  visit_tokens=False):
        self.__visit_tokens__ = visit_tokens

    def _call_userfunc(self, tree, new_children=None):
        # Assumes tree is already transformed
        children = new_children if new_children is not None else tree.children
        try:
            f = getattr(self, tree.data)
        except AttributeError:
            return self.__default__(tree.data, children, tree.meta)
        else:
            try:
                if getattr(f, 'meta', False):
                    return f(children, tree.meta)
                elif getattr(f, 'inline', False):
                    return f(*children)
                elif getattr(f, 'whole_tree', False):
                    if new_children is not None:
                        tree.children = new_children
                    return f(tree)
                else:
                    return f(children)
            except (GrammarError, Discard):
                raise
            except Exception as e:
                raise VisitError(tree, e)

    def _call_userfunc_token(self, token):
        try:
            f = getattr(self, token.type)
        except AttributeError:
            return self.__default_token__(token)
        else:
            try:
                return f(token)
            except (GrammarError, Discard):
                raise
            except Exception as e:
                raise VisitError(token, e)


    def _transform_children(self, children):
        for c in children:
            try:
                if isinstance(c, Tree):
                    yield self._transform_tree(c)
                elif self.__visit_tokens__ and isinstance(c, Token):
                    yield self._call_userfunc_token(c)
                else:
                    yield c
            except Discard:
                pass

    def _transform_tree(self, tree):
        children = list(self._transform_children(tree.children))
        return self._call_userfunc(tree, children)

    def transform(self, tree):
        return self._transform_tree(tree)

    def __mul__(self, other):
        return TransformerChain(self, other)

    def __default__(self, data, children, meta):
        "Default operation on tree (for override)"
        return Tree(data, children, meta)

    def __default_token__(self, token):
        "Default operation on token (for override)"
        return token


    @classmethod
    def _apply_decorator(cls, decorator, **kwargs):
        mro = getmro(cls)
        assert mro[0] is cls
        libmembers = {name for _cls in mro[1:] for name, _ in getmembers(_cls)}
        for name, value in getmembers(cls):

            # Make sure the function isn't inherited (unless it's overwritten)
            if name.startswith('_') or (name in libmembers and name not in cls.__dict__):
                continue
            if not callable(cls.__dict__[name]):
                continue

            # Skip if v_args already applied (at the function level)
            if hasattr(cls.__dict__[name], 'vargs_applied'):
                continue

            static = isinstance(cls.__dict__[name], (staticmethod, classmethod))
            setattr(cls, name, decorator(value, static=static, **kwargs))
        return cls


class InlineTransformer(Transformer):   # XXX Deprecated
    def _call_userfunc(self, tree, new_children=None):
        # Assumes tree is already transformed
        children = new_children if new_children is not None else tree.children
        try:
            f = getattr(self, tree.data)
        except AttributeError:
            return self.__default__(tree.data, children, tree.meta)
        else:
            return f(*children)


class TransformerChain(object):
    def __init__(self, *transformers):
        self.transformers = transformers

    def transform(self, tree):
        for t in self.transformers:
            tree = t.transform(tree)
        return tree

    def __mul__(self, other):
        return TransformerChain(*self.transformers + (other,))


class Transformer_InPlace(Transformer):
    "Non-recursive. Changes the tree in-place instead of returning new instances"
    def _transform_tree(self, tree):           # Cancel recursion
        return self._call_userfunc(tree)

    def transform(self, tree):
        for subtree in tree.iter_subtrees():
            subtree.children = list(self._transform_children(subtree.children))

        return self._transform_tree(tree)


class Transformer_InPlaceRecursive(Transformer):
    "Recursive. Changes the tree in-place instead of returning new instances"
    def _transform_tree(self, tree):
        tree.children = list(self._transform_children(tree.children))
        return self._call_userfunc(tree)



# Visitors

class VisitorBase:
    def _call_userfunc(self, tree):
        return getattr(self, tree.data, self.__default__)(tree)

    def __default__(self, tree):
        "Default operation on tree (for override)"
        return tree


class Visitor(VisitorBase):
    """Bottom-up visitor, non-recursive

    Visits the tree, starting with the leaves and finally the root (bottom-up)
    Calls its methods (provided by user via inheritance) according to tree.data
    """


    def visit(self, tree):
        for subtree in tree.iter_subtrees():
            self._call_userfunc(subtree)
        return tree

class Visitor_Recursive(VisitorBase):
    """Bottom-up visitor, recursive

    Visits the tree, starting with the leaves and finally the root (bottom-up)
    Calls its methods (provided by user via inheritance) according to tree.data
    """

    def visit(self, tree):
        for child in tree.children:
            if isinstance(child, Tree):
                self.visit(child)

        f = getattr(self, tree.data, self.__default__)
        f(tree)
        return tree



def visit_children_decor(func):
    "See Interpreter"
    @wraps(func)
    def inner(cls, tree):
        values = cls.visit_children(tree)
        return func(cls, values)
    return inner


class Interpreter:
    """Top-down visitor, recursive

    Visits the tree, starting with the root and finally the leaves (top-down)
    Calls its methods (provided by user via inheritance) according to tree.data

    Unlike Transformer and Visitor, the Interpreter doesn't automatically visit its sub-branches.
    The user has to explicitly call visit_children, or use the @visit_children_decor
    """
    def visit(self, tree):
        return getattr(self, tree.data)(tree)

    def visit_children(self, tree):
        return [self.visit(child) if isinstance(child, Tree) else child
                for child in tree.children]

    def __getattr__(self, name):
        return self.__default__

    def __default__(self, tree):
        return self.visit_children(tree)




# Decorators

def _apply_decorator(obj, decorator, **kwargs):
    try:
        _apply = obj._apply_decorator
    except AttributeError:
        return decorator(obj, **kwargs)
    else:
        return _apply(decorator, **kwargs)



def _inline_args__func(func):
    @wraps(func)
    def create_decorator(_f, with_self):
        if with_self:
            def f(self, children):
                return _f(self, *children)
        else:
            def f(self, children):
                return _f(*children)
        return f

    return smart_decorator(func, create_decorator)


def inline_args(obj):   # XXX Deprecated
    return _apply_decorator(obj, _inline_args__func)



def _visitor_args_func_dec(func, inline=False, meta=False, whole_tree=False, static=False):
    assert [whole_tree, meta, inline].count(True) <= 1
    def create_decorator(_f, with_self):
        if with_self:
            def f(self, *args, **kwargs):
                return _f(self, *args, **kwargs)
        else:
            def f(self, *args, **kwargs):
                return _f(*args, **kwargs)
        return f

    if static:
        f = wraps(func)(create_decorator(func, False))
    else:
        f = smart_decorator(func, create_decorator)
    f.vargs_applied = True
    f.inline = inline
    f.meta = meta
    f.whole_tree = whole_tree
    return f

def v_args(inline=False, meta=False, tree=False):
    "A convenience decorator factory, for modifying the behavior of user-supplied visitor methods"
    if [tree, meta, inline].count(True) > 1:
        raise ValueError("Visitor functions can either accept tree, or meta, or be inlined. These cannot be combined.")
    def _visitor_args_dec(obj):
        return _apply_decorator(obj, _visitor_args_func_dec, inline=inline, meta=meta, whole_tree=tree)
    return _visitor_args_dec


###}