170 lines
6.3 KiB
Python
170 lines
6.3 KiB
Python
# -*- coding: utf-8; -*-
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'''General utilities. Can be useful for writing both macros as well as macro expanders.'''
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__all__ = ['gensym', 'flatten_suite', 'rename',
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'format_location', 'format_macrofunction',
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'NestingLevelTracker']
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import ast
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from contextlib import contextmanager
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import uuid
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from . import walker
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_previous_gensyms = set()
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def gensym(basename=None):
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"""Create a name for a new, unused lexical identifier, and return the name as an `str`.
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We include an uuid in the name to avoid the need for any lexical scanning.
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Can also be used for globally unique string keys, in which case `basename`
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does not need to be a valid identifier.
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"""
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basename = basename or "gensym"
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def generate():
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unique = str(uuid.uuid4()).replace('-', '')
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return f"{basename}_{unique}"
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sym = generate()
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# The uuid spec does not guarantee no collisions, only a vanishingly small chance.
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while sym in _previous_gensyms:
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sym = generate() # pragma: no cover
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_previous_gensyms.add(sym)
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return sym
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def flatten_suite(lst):
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"""Flatten a statement suite (by one level).
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`lst` may contain both individual items and `list`s. Any item that
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`is None` is omitted. If the final result is empty, then instead of
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an empty list, return `None`. (This matches the AST representation
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of statement suites.)
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"""
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out = []
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for elt in lst:
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if isinstance(elt, list):
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out.extend(elt)
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elif elt is not None:
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out.append(elt)
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return out if out else None
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def rename(oldname, newname, tree):
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"""Rename all occurrences of a name in `tree`.
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We look in all places in the AST that hold name-like things.
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Currently: identifiers (names), attribute names, function and class names,
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function parameter names, arguments passed by name, name and asname in imports,
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and the as-part of an exception handler (binding a name to the exception object).
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Some constructs such as `For` and `With` use `Name` nodes for named things,
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so those are transformed too.
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With this you can do things like::
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from mcpyrate.quotes import macros, q
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from mcpyrate import gensym
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from mcpyrate.utils import rename
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tree = q[lambda _: ...]
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tree = rename("_", gensym(), tree)
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"""
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class Renamer(walker.Walker):
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def transform(self, tree):
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T = type(tree)
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if T is ast.Name:
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if tree.id == oldname:
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tree.id = newname
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# Look for "raw string" in GTS for a full list of the following.
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# https://greentreesnakes.readthedocs.io/en/latest/nodes.html
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elif T is ast.Attribute:
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if tree.attr == oldname:
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tree.attr = newname
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elif T in (ast.FunctionDef, ast.AsyncFunctionDef, ast.ClassDef):
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if tree.name == oldname:
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tree.name = newname
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elif T is ast.arg: # function parameter
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if tree.arg == oldname:
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tree.arg = newname
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elif T is ast.keyword: # in function call, argument passed by name
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if tree.arg == oldname:
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tree.arg = newname
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elif T is ast.alias: # in ast.Import, ast.ImportFrom
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if tree.name == oldname:
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tree.name = newname
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if tree.asname == oldname:
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tree.asname = newname
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elif T is ast.ExceptHandler:
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if tree.name == oldname:
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tree.name = newname
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return self.generic_visit(tree)
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return Renamer().visit(tree)
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# --------------------------------------------------------------------------------
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def format_location(filename, tree, sourcecode):
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'''Format a source code location in a standard way, for error messages.
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`filename`: full path to `.py` file.
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`tree`: AST node to get source line number from.
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`sourcecode`: source code (typically, to get this, `unparse(tree)`
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before expanding it), or `None` to omit it.
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'''
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lineno = tree.lineno if hasattr(tree, 'lineno') else None
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if sourcecode:
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sep = " " if "\n" not in sourcecode else "\n"
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source_with_sep = f"{sep}{sourcecode}"
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else:
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source_with_sep = ""
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return f'{filename}:{lineno}:{source_with_sep}'
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def format_macrofunction(function):
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'''Format the fully qualified name of a macro function, for error messages.'''
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if not function.__module__: # Macros defined in the REPL have `__module__=None`.
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return function.__qualname__
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return f"{function.__module__}.{function.__qualname__}"
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# --------------------------------------------------------------------------------
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class NestingLevelTracker:
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"""Track the nesting level in a set of co-operating, related macros.
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Useful for implementing macros that are syntactically only valid inside the
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invocation of another macro (i.e. when the level is `> 0`).
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Note that in order for level tracking to work, the context (outer) macros
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must expand inside-out (i.e. call `expander.visit` explicitly). If they
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expand outside-in (default), the outer macro invocation will already have
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exited when the inner macro invocation gets expanded.
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"""
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def __init__(self, start=0):
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"""start: int, initial level"""
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self.stack = [start]
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def _get_value(self):
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return self.stack[-1]
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value = property(fget=_get_value, doc="The current level. Read-only. Use `set_to` or `change_by` to change.")
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def set_to(self, value):
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"""Context manager. Run a section of code with the level set to `value`."""
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if not isinstance(value, int):
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raise TypeError(f"Expected integer `value`, got {type(value)} with value {repr(value)}")
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if value < 0:
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raise ValueError(f"`value` must be >= 0, got {repr(value)}")
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@contextmanager
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def _set_to():
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self.stack.append(value)
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try:
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yield
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finally:
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self.stack.pop()
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assert self.stack # postcondition
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return _set_to()
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def changed_by(self, delta):
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"""Context manager. Run a section of code with the level incremented by `delta`."""
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return self.set_to(self.value + delta)
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