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Implement delimited continuations (shift/reset) across all evaluators

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Bootstrap shift/reset to both Python and JS targets. The implementation
uses exception-based capture with re-evaluation: reset wraps in try/catch
for ShiftSignal, shift raises to the nearest reset, and continuation
invocation pushes a resume value and re-evaluates the body.

- Add Continuation type and _ShiftSignal to shared/sx/types.py
- Add sf_reset/sf_shift to hand-written evaluator.py
- Add async versions to async_eval.py
- Add shift/reset dispatch to eval.sx spec
- Bootstrap to Python: FIXUPS_PY with sf_reset/sf_shift, regenerate sx_ref.py
- Bootstrap to JS: Continuation/ShiftSignal types, sfReset/sfShift in fixups
- Add continuation? primitive to both bootstrappers and primitives.sx
- Allow callables (including Continuation) in hand-written HO map
- 44 unit tests (22 per evaluator) covering: passthrough, abort, invoke,
  double invoke, predicate, stored continuation, nested reset, practical patterns
- Update continuations essay to reflect implemented status with examples

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
giles
2026-03-06 00:58:50 +00:00
parent 12fe93bb55
commit 102a27e845
12 changed files with 480 additions and 15 deletions
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48
shared/sx/ref/sx_ref.py
View File

@@ -17,8 +17,8 @@ from typing import Any
# =========================================================================
from shared.sx.types import (
NIL, Symbol, Keyword, Lambda, Component, Macro, StyleValue,
HandlerDef, QueryDef, ActionDef, PageDef,
NIL, Symbol, Keyword, Lambda, Component, Continuation, Macro, StyleValue,
HandlerDef, QueryDef, ActionDef, PageDef, _ShiftSignal,
)
from shared.sx.parser import SxExpr
@@ -127,6 +127,8 @@ def type_of(x):
return "raw-html"
if isinstance(x, StyleValue):
return "style-value"
if isinstance(x, Continuation):
return "continuation"
if isinstance(x, list):
return "list"
if isinstance(x, dict):
@@ -467,7 +469,7 @@ _SPECIAL_FORM_NAMES = frozenset([
"define", "defcomp", "defmacro", "defstyle", "defkeyframes",
"defhandler", "defpage", "defquery", "defaction", "defrelation",
"begin", "do", "quote", "quasiquote",
"->", "set!",
"->", "set!", "reset", "shift",
])
_HO_FORM_NAMES = frozenset([
@@ -630,6 +632,11 @@ def aser_special(name, expr, env):
"defhandler", "defpage", "defquery", "defaction", "defrelation"):
trampoline(eval_expr(expr, env))
return NIL
# reset/shift — evaluate normally in aser mode (they're control flow)
if name == "reset":
return sf_reset(args, env)
if name == "shift":
return sf_shift(args, env)
# Lambda/fn, quote, quasiquote, set!, -> : evaluate normally
result = eval_expr(expr, env)
return trampoline(result)
@@ -715,6 +722,7 @@ PRIMITIVES["number?"] = lambda x: isinstance(x, (int, float)) and not isinstance
PRIMITIVES["string?"] = lambda x: isinstance(x, str)
PRIMITIVES["list?"] = lambda x: isinstance(x, _b_list)
PRIMITIVES["dict?"] = lambda x: isinstance(x, _b_dict)
PRIMITIVES["continuation?"] = lambda x: isinstance(x, Continuation)
PRIMITIVES["empty?"] = lambda c: (
c is None or c is NIL or
(isinstance(c, (_b_list, str, _b_dict)) and _b_len(c) == 0)
@@ -861,7 +869,7 @@ trampoline = lambda val: (lambda result: (trampoline(eval_expr(thunk_expr(result
eval_expr = lambda expr, env: _sx_case(type_of(expr), [('number', lambda: expr), ('string', lambda: expr), ('boolean', lambda: expr), ('nil', lambda: NIL), ('symbol', lambda: (lambda name: (env_get(env, name) if sx_truthy(env_has(env, name)) else (get_primitive(name) if sx_truthy(is_primitive(name)) else (True if sx_truthy((name == 'true')) else (False if sx_truthy((name == 'false')) else (NIL if sx_truthy((name == 'nil')) else error(sx_str('Undefined symbol: ', name))))))))(symbol_name(expr))), ('keyword', lambda: keyword_name(expr)), ('dict', lambda: map_dict(lambda k, v: trampoline(eval_expr(v, env)), expr)), ('list', lambda: ([] if sx_truthy(empty_p(expr)) else eval_list(expr, env))), (None, lambda: expr)])
# eval-list
eval_list = lambda expr, env: (lambda head: (lambda args: (map(lambda x: trampoline(eval_expr(x, env)), expr) if sx_truthy((not sx_truthy(((type_of(head) == 'symbol') if sx_truthy((type_of(head) == 'symbol')) else ((type_of(head) == 'lambda') if sx_truthy((type_of(head) == 'lambda')) else (type_of(head) == 'list')))))) else ((lambda name: (sf_if(args, env) if sx_truthy((name == 'if')) else (sf_when(args, env) if sx_truthy((name == 'when')) else (sf_cond(args, env) if sx_truthy((name == 'cond')) else (sf_case(args, env) if sx_truthy((name == 'case')) else (sf_and(args, env) if sx_truthy((name == 'and')) else (sf_or(args, env) if sx_truthy((name == 'or')) else (sf_let(args, env) if sx_truthy((name == 'let')) else (sf_let(args, env) if sx_truthy((name == 'let*')) else (sf_lambda(args, env) if sx_truthy((name == 'lambda')) else (sf_lambda(args, env) if sx_truthy((name == 'fn')) else (sf_define(args, env) if sx_truthy((name == 'define')) else (sf_defcomp(args, env) if sx_truthy((name == 'defcomp')) else (sf_defmacro(args, env) if sx_truthy((name == 'defmacro')) else (sf_defstyle(args, env) if sx_truthy((name == 'defstyle')) else (sf_defkeyframes(args, env) if sx_truthy((name == 'defkeyframes')) else (sf_defhandler(args, env) if sx_truthy((name == 'defhandler')) else (sf_defpage(args, env) if sx_truthy((name == 'defpage')) else (sf_defquery(args, env) if sx_truthy((name == 'defquery')) else (sf_defaction(args, env) if sx_truthy((name == 'defaction')) else (sf_begin(args, env) if sx_truthy((name == 'begin')) else (sf_begin(args, env) if sx_truthy((name == 'do')) else (sf_quote(args, env) if sx_truthy((name == 'quote')) else (sf_quasiquote(args, env) if sx_truthy((name == 'quasiquote')) else (sf_thread_first(args, env) if sx_truthy((name == '->')) else (sf_set_bang(args, env) if sx_truthy((name == 'set!')) else (ho_map(args, env) if sx_truthy((name == 'map')) else (ho_map_indexed(args, env) if sx_truthy((name == 'map-indexed')) else (ho_filter(args, env) if sx_truthy((name == 'filter')) else (ho_reduce(args, env) if sx_truthy((name == 'reduce')) else (ho_some(args, env) if sx_truthy((name == 'some')) else (ho_every(args, env) if sx_truthy((name == 'every?')) else (ho_for_each(args, env) if sx_truthy((name == 'for-each')) else ((lambda mac: make_thunk(expand_macro(mac, args, env), env))(env_get(env, name)) if sx_truthy((env_has(env, name) if not sx_truthy(env_has(env, name)) else is_macro(env_get(env, name)))) else (render_expr(expr, env) if sx_truthy(is_render_expr(expr)) else eval_call(head, args, env))))))))))))))))))))))))))))))))))))(symbol_name(head)) if sx_truthy((type_of(head) == 'symbol')) else eval_call(head, args, env))))(rest(expr)))(first(expr))
eval_list = lambda expr, env: (lambda head: (lambda args: (map(lambda x: trampoline(eval_expr(x, env)), expr) if sx_truthy((not sx_truthy(((type_of(head) == 'symbol') if sx_truthy((type_of(head) == 'symbol')) else ((type_of(head) == 'lambda') if sx_truthy((type_of(head) == 'lambda')) else (type_of(head) == 'list')))))) else ((lambda name: (sf_if(args, env) if sx_truthy((name == 'if')) else (sf_when(args, env) if sx_truthy((name == 'when')) else (sf_cond(args, env) if sx_truthy((name == 'cond')) else (sf_case(args, env) if sx_truthy((name == 'case')) else (sf_and(args, env) if sx_truthy((name == 'and')) else (sf_or(args, env) if sx_truthy((name == 'or')) else (sf_let(args, env) if sx_truthy((name == 'let')) else (sf_let(args, env) if sx_truthy((name == 'let*')) else (sf_lambda(args, env) if sx_truthy((name == 'lambda')) else (sf_lambda(args, env) if sx_truthy((name == 'fn')) else (sf_define(args, env) if sx_truthy((name == 'define')) else (sf_defcomp(args, env) if sx_truthy((name == 'defcomp')) else (sf_defmacro(args, env) if sx_truthy((name == 'defmacro')) else (sf_defstyle(args, env) if sx_truthy((name == 'defstyle')) else (sf_defkeyframes(args, env) if sx_truthy((name == 'defkeyframes')) else (sf_defhandler(args, env) if sx_truthy((name == 'defhandler')) else (sf_defpage(args, env) if sx_truthy((name == 'defpage')) else (sf_defquery(args, env) if sx_truthy((name == 'defquery')) else (sf_defaction(args, env) if sx_truthy((name == 'defaction')) else (sf_begin(args, env) if sx_truthy((name == 'begin')) else (sf_begin(args, env) if sx_truthy((name == 'do')) else (sf_quote(args, env) if sx_truthy((name == 'quote')) else (sf_quasiquote(args, env) if sx_truthy((name == 'quasiquote')) else (sf_thread_first(args, env) if sx_truthy((name == '->')) else (sf_set_bang(args, env) if sx_truthy((name == 'set!')) else (sf_reset(args, env) if sx_truthy((name == 'reset')) else (sf_shift(args, env) if sx_truthy((name == 'shift')) else (ho_map(args, env) if sx_truthy((name == 'map')) else (ho_map_indexed(args, env) if sx_truthy((name == 'map-indexed')) else (ho_filter(args, env) if sx_truthy((name == 'filter')) else (ho_reduce(args, env) if sx_truthy((name == 'reduce')) else (ho_some(args, env) if sx_truthy((name == 'some')) else (ho_every(args, env) if sx_truthy((name == 'every?')) else (ho_for_each(args, env) if sx_truthy((name == 'for-each')) else ((lambda mac: make_thunk(expand_macro(mac, args, env), env))(env_get(env, name)) if sx_truthy((env_has(env, name) if not sx_truthy(env_has(env, name)) else is_macro(env_get(env, name)))) else (render_expr(expr, env) if sx_truthy(is_render_expr(expr)) else eval_call(head, args, env))))))))))))))))))))))))))))))))))))))(symbol_name(head)) if sx_truthy((type_of(head) == 'symbol')) else eval_call(head, args, env))))(rest(expr)))(first(expr))
# eval-call
eval_call = lambda head, args, env: (lambda f: (lambda evaluated_args: (apply(f, evaluated_args) if sx_truthy((is_callable(f) if not sx_truthy(is_callable(f)) else ((not sx_truthy(is_lambda(f))) if not sx_truthy((not sx_truthy(is_lambda(f)))) else (not sx_truthy(is_component(f)))))) else (call_lambda(f, evaluated_args, env) if sx_truthy(is_lambda(f)) else (call_component(f, args, env) if sx_truthy(is_component(f)) else error(sx_str('Not callable: ', inspect(f)))))))(map(lambda a: trampoline(eval_expr(a, env)), args)))(trampoline(eval_expr(head, env)))
@@ -1100,6 +1108,38 @@ aser_fragment = lambda children, env: (lambda parts: ('' if sx_truthy(empty_p(pa
aser_call = lambda name, args, env: (lambda parts: _sx_begin(reduce(lambda state, arg: (lambda skip: (assoc(state, 'skip', False, 'i', (get(state, 'i') + 1)) if sx_truthy(skip) else ((lambda val: _sx_begin((_sx_begin(_sx_append(parts, sx_str(':', keyword_name(arg))), _sx_append(parts, serialize(val))) if sx_truthy((not sx_truthy(is_nil(val)))) else NIL), assoc(state, 'skip', True, 'i', (get(state, 'i') + 1))))(aser(nth(args, (get(state, 'i') + 1)), env)) if sx_truthy(((type_of(arg) == 'keyword') if not sx_truthy((type_of(arg) == 'keyword')) else ((get(state, 'i') + 1) < len(args)))) else (lambda val: _sx_begin((_sx_append(parts, serialize(val)) if sx_truthy((not sx_truthy(is_nil(val)))) else NIL), assoc(state, 'i', (get(state, 'i') + 1))))(aser(arg, env)))))(get(state, 'skip')), {'i': 0, 'skip': False}, args), sx_str('(', join(' ', parts), ')')))([name])
# =========================================================================
# Delimited continuations (shift/reset)
# =========================================================================
_RESET_RESUME = [] # stack of resume values; empty = not resuming
def sf_reset(args, env):
"""(reset body) -- establish a continuation delimiter."""
body = first(args)
try:
return trampoline(eval_expr(body, env))
except _ShiftSignal as sig:
def cont_fn(value=NIL):
_RESET_RESUME.append(value)
try:
return trampoline(eval_expr(body, env))
finally:
_RESET_RESUME.pop()
k = Continuation(cont_fn)
sig_env = dict(sig.env)
sig_env[sig.k_name] = k
return trampoline(eval_expr(sig.body, sig_env))
def sf_shift(args, env):
"""(shift k body) -- capture continuation to nearest reset."""
if _RESET_RESUME:
return _RESET_RESUME[-1]
k_name = symbol_name(first(args))
body = nth(args, 1)
raise _ShiftSignal(k_name, body, env)
# =========================================================================
# Fixups -- wire up render adapter dispatch
# =========================================================================