giles
0fb87e3b1c
S-expression parser, evaluator, and primitive registry in shared/sexp/. 109 unit tests covering parsing, evaluation, special forms, lambdas, closures, components (defcomp), and 60+ pure builtins. Test infrastructure: Dockerfile.unit (tier 1, fast) and Dockerfile.integration (tier 2, ffmpeg). Dev watch mode auto-reruns on file changes. Deploy gate blocks push on test failure. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
550 lines
17 KiB
Python
550 lines
17 KiB
Python
"""
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S-expression evaluator.
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Walks a parsed s-expression tree and evaluates it in an environment.
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Special forms:
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(if cond then else?)
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(when cond body)
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(cond clause...) — Scheme-style ((test body)...) or Clojure-style (test body...)
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(case expr val body... :else default)
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(and expr...) (or expr...)
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(let ((name val)...) body) or (let (name val name val...) body)
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(lambda (params...) body) or (fn (params...) body)
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(define name value)
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(defcomp ~name (&key param...) body)
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(begin expr...)
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(quote expr)
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(do expr...) — alias for begin
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(-> val form...) — thread-first macro
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Higher-order forms (operate on lambdas):
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(map fn coll)
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(map-indexed fn coll)
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(filter fn coll)
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(reduce fn init coll)
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(some fn coll)
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(every? fn coll)
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(for-each fn coll)
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"""
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from __future__ import annotations
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from typing import Any
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from .types import Component, Keyword, Lambda, NIL, Symbol
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from .primitives import _PRIMITIVES
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class EvalError(Exception):
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"""Error during expression evaluation."""
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pass
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# ---------------------------------------------------------------------------
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# Public API
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# ---------------------------------------------------------------------------
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def evaluate(expr: Any, env: dict[str, Any] | None = None) -> Any:
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"""Evaluate *expr* in *env* and return the result."""
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if env is None:
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env = {}
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return _eval(expr, env)
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def make_env(**kwargs: Any) -> dict[str, Any]:
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"""Convenience: create an environment dict with initial bindings."""
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return dict(kwargs)
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# ---------------------------------------------------------------------------
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# Internal evaluator
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# ---------------------------------------------------------------------------
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def _eval(expr: Any, env: dict[str, Any]) -> Any:
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# --- literals ---------------------------------------------------------
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if isinstance(expr, (int, float, str, bool)):
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return expr
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if expr is None or expr is NIL:
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return NIL
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# --- symbol lookup ----------------------------------------------------
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if isinstance(expr, Symbol):
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name = expr.name
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if name in env:
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return env[name]
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if name in _PRIMITIVES:
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return _PRIMITIVES[name]
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if name == "true":
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return True
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if name == "false":
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return False
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if name == "nil":
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return NIL
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raise EvalError(f"Undefined symbol: {name}")
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# --- keyword → its string name ----------------------------------------
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if isinstance(expr, Keyword):
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return expr.name
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# --- dict literal -----------------------------------------------------
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if isinstance(expr, dict):
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return {k: _eval(v, env) for k, v in expr.items()}
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# --- list = call or special form --------------------------------------
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if not isinstance(expr, list):
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return expr
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if not expr:
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return []
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head = expr[0]
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# If head is not a symbol/lambda/list, treat entire list as data
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if not isinstance(head, (Symbol, Lambda, list)):
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return [_eval(x, env) for x in expr]
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# --- special forms ----------------------------------------------------
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if isinstance(head, Symbol):
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name = head.name
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handler = _SPECIAL_FORMS.get(name)
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if handler is not None:
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return handler(expr, env)
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# Higher-order forms (need lazy eval of lambda arg)
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ho = _HO_FORMS.get(name)
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if ho is not None:
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return ho(expr, env)
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# --- function / lambda call -------------------------------------------
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fn = _eval(head, env)
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args = [_eval(a, env) for a in expr[1:]]
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if callable(fn) and not isinstance(fn, (Lambda, Component)):
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return fn(*args)
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if isinstance(fn, Lambda):
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return _call_lambda(fn, args, env)
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if isinstance(fn, Component):
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return _call_component(fn, expr[1:], env)
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raise EvalError(f"Not callable: {fn!r}")
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# ---------------------------------------------------------------------------
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# Lambda / component invocation
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# ---------------------------------------------------------------------------
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def _call_lambda(fn: Lambda, args: list[Any], caller_env: dict[str, Any]) -> Any:
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if len(args) != len(fn.params):
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raise EvalError(f"{fn!r} expects {len(fn.params)} args, got {len(args)}")
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local = dict(fn.closure)
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local.update(caller_env)
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for p, v in zip(fn.params, args):
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local[p] = v
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return _eval(fn.body, local)
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def _call_component(comp: Component, raw_args: list[Any], env: dict[str, Any]) -> Any:
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"""Evaluate a component invocation with keyword arguments.
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``(~card :title "Hello" (p "child"))``
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→ comp.params gets ``title="Hello"``, comp children gets ``[(p "child")]``
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"""
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kwargs: dict[str, Any] = {}
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children: list[Any] = []
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i = 0
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while i < len(raw_args):
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arg = raw_args[i]
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if isinstance(arg, Keyword) and i + 1 < len(raw_args):
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kwargs[arg.name] = _eval(raw_args[i + 1], env)
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i += 2
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else:
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children.append(_eval(arg, env))
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i += 1
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local = dict(comp.closure)
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local.update(env)
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for p in comp.params:
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if p in kwargs:
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local[p] = kwargs[p]
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else:
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local[p] = NIL
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if comp.has_children:
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local["children"] = children
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return _eval(comp.body, local)
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# ---------------------------------------------------------------------------
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# Special forms
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# ---------------------------------------------------------------------------
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def _sf_if(expr: list, env: dict) -> Any:
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if len(expr) < 3:
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raise EvalError("if requires condition and then-branch")
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cond = _eval(expr[1], env)
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if cond and cond is not NIL:
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return _eval(expr[2], env)
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if len(expr) > 3:
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return _eval(expr[3], env)
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return NIL
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def _sf_when(expr: list, env: dict) -> Any:
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if len(expr) < 3:
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raise EvalError("when requires condition and body")
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cond = _eval(expr[1], env)
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if cond and cond is not NIL:
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result = NIL
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for body_expr in expr[2:]:
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result = _eval(body_expr, env)
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return result
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return NIL
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def _sf_cond(expr: list, env: dict) -> Any:
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clauses = expr[1:]
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if not clauses:
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return NIL
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# Detect scheme-style: first clause is a 2-element list that isn't a comparison
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if (
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isinstance(clauses[0], list)
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and len(clauses[0]) == 2
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and not (isinstance(clauses[0][0], Symbol) and clauses[0][0].name in (
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"=", "<", ">", "<=", ">=", "!=", "and", "or",
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))
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):
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for clause in clauses:
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if not isinstance(clause, list) or len(clause) < 2:
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raise EvalError("cond clause must be (test result)")
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test = clause[0]
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if isinstance(test, Symbol) and test.name in ("else", ":else"):
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return _eval(clause[1], env)
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if isinstance(test, Keyword) and test.name == "else":
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return _eval(clause[1], env)
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if _eval(test, env):
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return _eval(clause[1], env)
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else:
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i = 0
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while i < len(clauses) - 1:
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test = clauses[i]
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result = clauses[i + 1]
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if isinstance(test, Keyword) and test.name == "else":
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return _eval(result, env)
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if isinstance(test, Symbol) and test.name in (":else", "else"):
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return _eval(result, env)
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if _eval(test, env):
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return _eval(result, env)
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i += 2
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return NIL
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def _sf_case(expr: list, env: dict) -> Any:
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if len(expr) < 2:
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raise EvalError("case requires expression to match")
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match_val = _eval(expr[1], env)
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clauses = expr[2:]
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i = 0
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while i < len(clauses) - 1:
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test = clauses[i]
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result = clauses[i + 1]
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if isinstance(test, Keyword) and test.name == "else":
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return _eval(result, env)
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if isinstance(test, Symbol) and test.name in (":else", "else"):
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return _eval(result, env)
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if match_val == _eval(test, env):
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return _eval(result, env)
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i += 2
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return NIL
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def _sf_and(expr: list, env: dict) -> Any:
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result: Any = True
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for arg in expr[1:]:
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result = _eval(arg, env)
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if not result:
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return result
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return result
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def _sf_or(expr: list, env: dict) -> Any:
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result: Any = False
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for arg in expr[1:]:
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result = _eval(arg, env)
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if result:
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return result
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return result
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def _sf_let(expr: list, env: dict) -> Any:
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if len(expr) < 3:
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raise EvalError("let requires bindings and body")
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bindings = expr[1]
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local = dict(env)
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if isinstance(bindings, list):
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if bindings and isinstance(bindings[0], list):
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# Scheme-style: ((name val) ...)
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for binding in bindings:
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if len(binding) != 2:
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raise EvalError("let binding must be (name value)")
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var = binding[0]
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vname = var.name if isinstance(var, Symbol) else var
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local[vname] = _eval(binding[1], local)
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elif len(bindings) % 2 == 0:
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# Clojure-style: (name val name val ...)
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for i in range(0, len(bindings), 2):
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var = bindings[i]
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vname = var.name if isinstance(var, Symbol) else var
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local[vname] = _eval(bindings[i + 1], local)
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else:
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raise EvalError("let bindings must be (name val ...) pairs")
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else:
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raise EvalError("let bindings must be a list")
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# Evaluate body expressions, return last
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result: Any = NIL
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for body_expr in expr[2:]:
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result = _eval(body_expr, local)
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return result
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def _sf_lambda(expr: list, env: dict) -> Lambda:
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if len(expr) < 3:
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raise EvalError("lambda requires params and body")
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params_expr = expr[1]
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if not isinstance(params_expr, list):
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raise EvalError("lambda params must be a list")
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param_names = []
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for p in params_expr:
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if isinstance(p, Symbol):
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param_names.append(p.name)
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elif isinstance(p, str):
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param_names.append(p)
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else:
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raise EvalError(f"Invalid lambda param: {p}")
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return Lambda(param_names, expr[2], dict(env))
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def _sf_define(expr: list, env: dict) -> Any:
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if len(expr) < 3:
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raise EvalError("define requires name and value")
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name_sym = expr[1]
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if not isinstance(name_sym, Symbol):
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raise EvalError(f"define name must be symbol, got {type(name_sym).__name__}")
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value = _eval(expr[2], env)
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if isinstance(value, Lambda) and value.name is None:
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value.name = name_sym.name
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env[name_sym.name] = value
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return value
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def _sf_defcomp(expr: list, env: dict) -> Component:
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"""``(defcomp ~name (&key param1 param2 &rest children) body)``"""
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if len(expr) < 4:
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raise EvalError("defcomp requires name, params, and body")
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name_sym = expr[1]
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if not isinstance(name_sym, Symbol):
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raise EvalError(f"defcomp name must be symbol, got {type(name_sym).__name__}")
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comp_name = name_sym.name.lstrip("~")
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params_expr = expr[2]
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if not isinstance(params_expr, list):
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raise EvalError("defcomp params must be a list")
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params: list[str] = []
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has_children = False
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in_key = False
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for p in params_expr:
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if isinstance(p, Symbol):
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if p.name == "&key":
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in_key = True
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continue
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if p.name == "&rest":
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has_children = True
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continue
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if in_key or has_children:
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if not has_children:
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params.append(p.name)
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else:
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params.append(p.name)
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# Skip children param name after &rest
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elif isinstance(p, str):
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params.append(p)
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comp = Component(
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name=comp_name,
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params=params,
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has_children=has_children,
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body=expr[3],
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closure=dict(env),
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)
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env[name_sym.name] = comp
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return comp
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def _sf_begin(expr: list, env: dict) -> Any:
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result: Any = NIL
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for sub in expr[1:]:
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result = _eval(sub, env)
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return result
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def _sf_quote(expr: list, _env: dict) -> Any:
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return expr[1] if len(expr) > 1 else NIL
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def _sf_thread_first(expr: list, env: dict) -> Any:
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"""``(-> val (f a) (g b))`` → ``(g (f val a) b)``"""
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if len(expr) < 2:
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raise EvalError("-> requires at least a value")
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result = _eval(expr[1], env)
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for form in expr[2:]:
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if isinstance(form, list):
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fn = _eval(form[0], env)
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args = [result] + [_eval(a, env) for a in form[1:]]
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else:
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fn = _eval(form, env)
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args = [result]
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if callable(fn) and not isinstance(fn, (Lambda, Component)):
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result = fn(*args)
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elif isinstance(fn, Lambda):
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result = _call_lambda(fn, args, env)
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else:
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raise EvalError(f"-> form not callable: {fn!r}")
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return result
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def _sf_set_bang(expr: list, env: dict) -> Any:
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"""``(set! name value)`` — mutate existing binding."""
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if len(expr) != 3:
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raise EvalError("set! requires name and value")
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name_sym = expr[1]
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if not isinstance(name_sym, Symbol):
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raise EvalError(f"set! name must be symbol, got {type(name_sym).__name__}")
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value = _eval(expr[2], env)
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# Walk up scope if using Env objects; for plain dicts just overwrite
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env[name_sym.name] = value
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return value
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_SPECIAL_FORMS: dict[str, Any] = {
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"if": _sf_if,
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"when": _sf_when,
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"cond": _sf_cond,
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"case": _sf_case,
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"and": _sf_and,
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"or": _sf_or,
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"let": _sf_let,
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"let*": _sf_let,
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"lambda": _sf_lambda,
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"fn": _sf_lambda,
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"define": _sf_define,
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"defcomp": _sf_defcomp,
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"begin": _sf_begin,
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"do": _sf_begin,
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"quote": _sf_quote,
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"->": _sf_thread_first,
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"set!": _sf_set_bang,
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}
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# ---------------------------------------------------------------------------
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# Higher-order forms (need to evaluate the fn arg first)
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# ---------------------------------------------------------------------------
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def _ho_map(expr: list, env: dict) -> list:
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if len(expr) != 3:
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raise EvalError("map requires fn and collection")
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fn = _eval(expr[1], env)
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coll = _eval(expr[2], env)
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if not isinstance(fn, Lambda):
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raise EvalError(f"map requires lambda, got {type(fn).__name__}")
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return [_call_lambda(fn, [item], env) for item in coll]
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def _ho_map_indexed(expr: list, env: dict) -> list:
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if len(expr) != 3:
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raise EvalError("map-indexed requires fn and collection")
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fn = _eval(expr[1], env)
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coll = _eval(expr[2], env)
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if not isinstance(fn, Lambda):
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raise EvalError(f"map-indexed requires lambda, got {type(fn).__name__}")
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if len(fn.params) < 2:
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raise EvalError("map-indexed lambda needs (i item) params")
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return [_call_lambda(fn, [i, item], env) for i, item in enumerate(coll)]
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def _ho_filter(expr: list, env: dict) -> list:
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if len(expr) != 3:
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raise EvalError("filter requires fn and collection")
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fn = _eval(expr[1], env)
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coll = _eval(expr[2], env)
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if not isinstance(fn, Lambda):
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raise EvalError(f"filter requires lambda, got {type(fn).__name__}")
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return [item for item in coll if _call_lambda(fn, [item], env)]
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def _ho_reduce(expr: list, env: dict) -> Any:
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if len(expr) != 4:
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raise EvalError("reduce requires fn, init, and collection")
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fn = _eval(expr[1], env)
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acc = _eval(expr[2], env)
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coll = _eval(expr[3], env)
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if not isinstance(fn, Lambda):
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raise EvalError(f"reduce requires lambda, got {type(fn).__name__}")
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for item in coll:
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acc = _call_lambda(fn, [acc, item], env)
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return acc
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def _ho_some(expr: list, env: dict) -> Any:
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if len(expr) != 3:
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raise EvalError("some requires fn and collection")
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fn = _eval(expr[1], env)
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coll = _eval(expr[2], env)
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if not isinstance(fn, Lambda):
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raise EvalError(f"some requires lambda, got {type(fn).__name__}")
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for item in coll:
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result = _call_lambda(fn, [item], env)
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if result:
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return result
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return NIL
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def _ho_every(expr: list, env: dict) -> bool:
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if len(expr) != 3:
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raise EvalError("every? requires fn and collection")
|
|
fn = _eval(expr[1], env)
|
|
coll = _eval(expr[2], env)
|
|
if not isinstance(fn, Lambda):
|
|
raise EvalError(f"every? requires lambda, got {type(fn).__name__}")
|
|
for item in coll:
|
|
if not _call_lambda(fn, [item], env):
|
|
return False
|
|
return True
|
|
|
|
|
|
def _ho_for_each(expr: list, env: dict) -> Any:
|
|
if len(expr) != 3:
|
|
raise EvalError("for-each requires fn and collection")
|
|
fn = _eval(expr[1], env)
|
|
coll = _eval(expr[2], env)
|
|
if not isinstance(fn, Lambda):
|
|
raise EvalError(f"for-each requires lambda, got {type(fn).__name__}")
|
|
for item in coll:
|
|
_call_lambda(fn, [item], env)
|
|
return NIL
|
|
|
|
|
|
_HO_FORMS: dict[str, Any] = {
|
|
"map": _ho_map,
|
|
"map-indexed": _ho_map_indexed,
|
|
"filter": _ho_filter,
|
|
"reduce": _ho_reduce,
|
|
"some": _ho_some,
|
|
"every?": _ho_every,
|
|
"for-each": _ho_for_each,
|
|
}
|