giles
e8bc228c7f
Rename all sexp directories, files, identifiers, and references to sx. artdag/ excluded (separate media processing DSL). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
98 lines
2.9 KiB
Python
98 lines
2.9 KiB
Python
"""
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Lexical environment for s-expression evaluation.
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Environments form a parent chain so inner scopes shadow outer ones
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while still allowing lookup of free variables.
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"""
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from __future__ import annotations
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from typing import Any
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class Env:
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"""A lexical scope mapping names → values with an optional parent."""
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__slots__ = ("_bindings", "_parent")
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def __init__(
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self,
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bindings: dict[str, Any] | None = None,
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parent: Env | None = None,
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):
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self._bindings: dict[str, Any] = bindings or {}
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self._parent = parent
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# -- lookup -------------------------------------------------------------
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def lookup(self, name: str) -> Any:
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"""Resolve *name*, walking the parent chain.
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Raises ``KeyError`` if not found.
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"""
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if name in self._bindings:
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return self._bindings[name]
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if self._parent is not None:
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return self._parent.lookup(name)
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raise KeyError(name)
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def __contains__(self, name: str) -> bool:
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if name in self._bindings:
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return True
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if self._parent is not None:
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return name in self._parent
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return False
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def __getitem__(self, name: str) -> Any:
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return self.lookup(name)
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def get(self, name: str, default: Any = None) -> Any:
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try:
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return self.lookup(name)
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except KeyError:
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return default
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# -- mutation -----------------------------------------------------------
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def define(self, name: str, value: Any) -> None:
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"""Bind *name* in the **current** scope."""
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self._bindings[name] = value
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def set(self, name: str, value: Any) -> None:
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"""Update *name* in the **nearest enclosing** scope that contains it.
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Raises ``KeyError`` if the name is not bound anywhere.
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"""
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if name in self._bindings:
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self._bindings[name] = value
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elif self._parent is not None:
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self._parent.set(name, value)
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else:
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raise KeyError(f"Cannot set! undefined variable: {name}")
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# -- construction -------------------------------------------------------
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def extend(self, bindings: dict[str, Any] | None = None) -> Env:
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"""Return a child environment."""
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return Env(bindings or {}, parent=self)
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# -- conversion ---------------------------------------------------------
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def to_dict(self) -> dict[str, Any]:
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"""Flatten the full chain into a single dict (parent first)."""
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if self._parent is not None:
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d = self._parent.to_dict()
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else:
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d = {}
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d.update(self._bindings)
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return d
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def __repr__(self) -> str:
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keys = list(self._bindings.keys())
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depth = 0
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p = self._parent
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while p:
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depth += 1
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p = p._parent
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return f"<Env depth={depth} keys={keys}>"
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