FA-3581 / Lexical grammars / Open access

A simplified mailbox has empty dot-separated local segments · case 01

A simplified mailbox has empty dot-separated local segments.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The recognizer uses '[A-Za-z0-9.]+@[A-Za-z.]+', which admits or omits a token shape forbidden by the stated grammar.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Accept ASCII alphanumeric local segments separated by dots, @, then letter-only dot-separated domain labels.

Unsuccessful approach: The candidate grammar '[A-Za-z0-9]+(?:\\.[A-Za-z0-9]+)*@[A-Za-z.]+' still disagrees with the explicit boundary fixtures.

Case contract

Accept ASCII alphanumeric local segments separated by dots, @, then letter-only dot-separated domain labels.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return bool(re.fullmatch('[A-Za-z0-9.]+@[A-Za-z.]+',x))
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('a..b@example.com'), False)
check('boundary 2', solve('a@example..com'), False)
check('boundary 3', solve('a.b@example.com'), True)
check('boundary 4', solve('a@x.y'), True)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`True`	`False`	Failed
boundary 2	`True`	`False`	Failed
boundary 3	`True`	`True`	Passed
boundary 4	`True`	`True`	Passed

SHA-256 / eedfc01d3810bae286521148dc4c51825e3bac213ec3bada7679bff793407b6d

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return bool(re.fullmatch('[A-Za-z0-9]+(?:\\.[A-Za-z0-9]+)*@[A-Za-z.]+',x))
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('a..b@example.com'), False)
check('boundary 2', solve('a@example..com'), False)
check('boundary 3', solve('a.b@example.com'), True)
check('boundary 4', solve('a@x.y'), True)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`False`	`False`	Passed
boundary 2	`True`	`False`	Failed
boundary 3	`True`	`True`	Passed
boundary 4	`True`	`True`	Passed

SHA-256 / 82c508a7f697fa55995765e0f2db6832684f6d172ae9d1683e00d510035163c1

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return bool(re.fullmatch('[A-Za-z0-9]+(?:\\.[A-Za-z0-9]+)*@[A-Za-z]+(?:\\.[A-Za-z]+)+',x))
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('a..b@example.com'), False)
check('boundary 2', solve('a@example..com'), False)
check('boundary 3', solve('a.b@example.com'), True)
check('boundary 4', solve('a@x.y'), True)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`False`	`False`	Passed
boundary 2	`False`	`False`	Passed
boundary 3	`True`	`True`	Passed
boundary 4	`True`	`True`	Passed

SHA-256 / 5f11bef7e98d2434ab3cd3f8b1c85d69f800e9f42701f53b048d6934af61e0e8

Verification & scope

This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:37:28.020172+00:00.

Case digest / 095f776964e0ef729687601fc0b44679e23d5ee05dffa751950aeeb4aa1cfcde