from abc import ABC from functools import wraps from .utils import smart_decorator, combine_alternatives from .tree import Tree from .exceptions import VisitError, GrammarError from .lexer import Token ###{standalone from inspect import getmembers, getmro from typing import TypeVar, Tuple, List, Callable, Generic, Type, Union, Optional _T = TypeVar('_T') _R = TypeVar('_R') _FUNC = Callable[..., _T] _DECORATED = Union[_FUNC, type] class Discard(Exception): """When raising the Discard exception in a transformer callback, that node is discarded and won't appear in the parent. """ pass # Transformers class _Decoratable: "Provides support for decorating methods with @v_args" @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(value): continue # Skip if v_args already applied (at the function level) if hasattr(cls.__dict__[name], 'vargs_applied') or hasattr(value, 'vargs_applied'): continue static = isinstance(cls.__dict__[name], (staticmethod, classmethod)) setattr(cls, name, decorator(value, static=static, **kwargs)) return cls def __class_getitem__(cls, _): return cls class Transformer(_Decoratable, ABC, Generic[_T]): """Transformers visit each node of the tree, and run the appropriate method on it according to the node's data. Methods are provided by the user via inheritance, and called according to ``tree.data``. The returned value from each method replaces the node in the tree structure. Transformers work bottom-up (or depth-first), starting with the leaves and ending at the root of the tree. Transformers can be used to implement map & reduce patterns. Because nodes are reduced from leaf to root, at any point the callbacks may assume the children have already been transformed (if applicable). ``Transformer`` can do anything ``Visitor`` can do, but because it reconstructs the tree, it is slightly less efficient. All these classes implement the transformer interface: - ``Transformer`` - Recursively transforms the tree. This is the one you probably want. - ``Transformer_InPlace`` - Non-recursive. Changes the tree in-place instead of returning new instances - ``Transformer_InPlaceRecursive`` - Recursive. Changes the tree in-place instead of returning new instances Parameters: visit_tokens (bool, optional): Should the transformer visit tokens in addition to rules. Setting this to ``False`` is slightly faster. Defaults to ``True``. (For processing ignored tokens, use the ``lexer_callbacks`` options) NOTE: A transformer without methods essentially performs a non-memoized partial deepcopy. """ __visit_tokens__ = True # For backwards compatibility def __init__(self, visit_tokens: bool=True) -> None: 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: wrapper = getattr(f, 'visit_wrapper', None) if wrapper is not None: return f.visit_wrapper(f, tree.data, children, tree.meta) else: return f(children) except (GrammarError, Discard): raise except Exception as e: raise VisitError(tree.data, 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.type, 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: Tree) -> _T: "Transform the given tree, and return the final result" return self._transform_tree(tree) def __mul__(self, other: 'Transformer[_T]') -> 'TransformerChain[_T]': """Chain two transformers together, returning a new transformer. """ return TransformerChain(self, other) def __default__(self, data, children, meta): """Default function that is called if there is no attribute matching ``data`` Can be overridden. Defaults to creating a new copy of the tree node (i.e. ``return Tree(data, children, meta)``) """ return Tree(data, children, meta) def __default_token__(self, token): """Default function that is called if there is no attribute matching ``token.type`` Can be overridden. Defaults to returning the token as-is. """ return token class TransformerChain(Generic[_T]): transformers: Tuple[Transformer[_T], ...] def __init__(self, *transformers: Transformer[_T]) -> None: self.transformers = transformers def transform(self, tree: Tree) -> _T: for t in self.transformers: tree = t.transform(tree) return tree def __mul__(self, other: Transformer[_T]) -> 'TransformerChain[_T]': return TransformerChain(*self.transformers + (other,)) class Transformer_InPlace(Transformer): """Same as Transformer, but non-recursive, and changes the tree in-place instead of returning new instances Useful for huge trees. Conservative in memory. """ 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_NonRecursive(Transformer): """Same as Transformer but non-recursive. Like Transformer, it doesn't change the original tree. Useful for huge trees. """ def transform(self, tree): # Tree to postfix rev_postfix = [] q = [tree] while q: t = q.pop() rev_postfix.append(t) if isinstance(t, Tree): q += t.children # Postfix to tree stack = [] for x in reversed(rev_postfix): if isinstance(x, Tree): size = len(x.children) if size: args = stack[-size:] del stack[-size:] else: args = [] stack.append(self._call_userfunc(x, args)) elif self.__visit_tokens__ and isinstance(x, Token): stack.append(self._call_userfunc_token(x)) else: stack.append(x) t ,= stack # We should have only one tree remaining return t class Transformer_InPlaceRecursive(Transformer): "Same as Transformer, recursive, but 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 function that is called if there is no attribute matching ``tree.data`` Can be overridden. Defaults to doing nothing. """ return tree def __class_getitem__(cls, _): return cls class Visitor(VisitorBase, ABC, Generic[_T]): """Tree visitor, non-recursive (can handle huge trees). Visiting a node calls its methods (provided by the user via inheritance) according to ``tree.data`` """ def visit(self, tree: Tree) -> Tree: "Visits the tree, starting with the leaves and finally the root (bottom-up)" for subtree in tree.iter_subtrees(): self._call_userfunc(subtree) return tree def visit_topdown(self, tree: Tree) -> Tree: "Visit the tree, starting at the root, and ending at the leaves (top-down)" for subtree in tree.iter_subtrees_topdown(): self._call_userfunc(subtree) return tree class Visitor_Recursive(VisitorBase): """Bottom-up visitor, recursive. Visiting a node calls its methods (provided by the user via inheritance) according to ``tree.data`` Slightly faster than the non-recursive version. """ def visit(self, tree: Tree) -> Tree: "Visits the tree, starting with the leaves and finally the root (bottom-up)" for child in tree.children: if isinstance(child, Tree): self.visit(child) self._call_userfunc(tree) return tree def visit_topdown(self,tree: Tree) -> Tree: "Visit the tree, starting at the root, and ending at the leaves (top-down)" self._call_userfunc(tree) for child in tree.children: if isinstance(child, Tree): self.visit_topdown(child) return tree class Interpreter(_Decoratable, ABC, Generic[_T]): """Interpreter walks the tree starting at the root. Visits the tree, starting with the root and finally the leaves (top-down) For each tree node, it 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``, ``visit_children``, or use the ``@visit_children_decor``. This allows the user to implement branching and loops. """ def visit(self, tree: Tree) -> _T: f = getattr(self, tree.data) wrapper = getattr(f, 'visit_wrapper', None) if wrapper is not None: return f.visit_wrapper(f, tree.data, tree.children, tree.meta) else: return f(tree) def visit_children(self, tree: Tree) -> List[_T]: 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) _InterMethod = Callable[[Type[Interpreter], _T], _R] def visit_children_decor(func: _InterMethod) -> _InterMethod: "See Interpreter" @wraps(func) def inner(cls, tree): values = cls.visit_children(tree) return func(cls, values) return inner # 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 _visitor_args_func_dec(func, visit_wrapper=None, static=False): 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.visit_wrapper = visit_wrapper return f def _vargs_inline(f, _data, children, _meta): return f(*children) def _vargs_meta_inline(f, _data, children, meta): return f(meta, *children) def _vargs_meta(f, _data, children, meta): return f(children, meta) # TODO swap these for consistency? Backwards incompatible! def _vargs_tree(f, data, children, meta): return f(Tree(data, children, meta)) def v_args(inline: bool=False, meta: bool=False, tree: bool=False, wrapper: Optional[Callable]=None) -> Callable[[_DECORATED], _DECORATED]: """A convenience decorator factory for modifying the behavior of user-supplied visitor methods. By default, callback methods of transformers/visitors accept one argument - a list of the node's children. ``v_args`` can modify this behavior. When used on a transformer/visitor class definition, it applies to all the callback methods inside it. ``v_args`` can be applied to a single method, or to an entire class. When applied to both, the options given to the method take precedence. Parameters: inline (bool, optional): Children are provided as ``*args`` instead of a list argument (not recommended for very long lists). meta (bool, optional): Provides two arguments: ``children`` and ``meta`` (instead of just the first) tree (bool, optional): Provides the entire tree as the argument, instead of the children. wrapper (function, optional): Provide a function to decorate all methods. Example: :: @v_args(inline=True) class SolveArith(Transformer): def add(self, left, right): return left + right class ReverseNotation(Transformer_InPlace): @v_args(tree=True) def tree_node(self, tree): tree.children = tree.children[::-1] """ if tree and (meta or inline): raise ValueError("Visitor functions cannot combine 'tree' with 'meta' or 'inline'.") func = None if meta: if inline: func = _vargs_meta_inline else: func = _vargs_meta elif inline: func = _vargs_inline elif tree: func = _vargs_tree if wrapper is not None: if func is not None: raise ValueError("Cannot use 'wrapper' along with 'tree', 'meta' or 'inline'.") func = wrapper def _visitor_args_dec(obj): return _apply_decorator(obj, _visitor_args_func_dec, visit_wrapper=func) return _visitor_args_dec ###} # --- Visitor Utilities --- class CollapseAmbiguities(Transformer): """ Transforms a tree that contains any number of _ambig nodes into a list of trees, each one containing an unambiguous tree. The length of the resulting list is the product of the length of all _ambig nodes. Warning: This may quickly explode for highly ambiguous trees. """ def _ambig(self, options): return sum(options, []) def __default__(self, data, children_lists, meta): return [Tree(data, children, meta) for children in combine_alternatives(children_lists)] def __default_token__(self, t): return [t]