Bug in regular expression semantics?

# Joshua Cranmer (13 years ago)

I am currently working on building an executable version of the semantics of regular expression pattern matching, and I think I've found in a bug in how they are specified in both the released version of ECMA-262 and the latest working draft.

In §15.10.2.5, it says that: The production Term :: Assertion evaluates by returning an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:

Evaluate Assertion to obtain an AssertionTester t. [ ... ]

However, the definition of the negative and positive lookahead assertions in §15.10.2.6 do not return AssertionTesters (like the ^, $, \b, and \B assertions do) but matchers: The production Assertion :: ( ? = Disjunction ) evaluates as follows:

Evaluate Disjunction to obtain a Matcher m.
Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following steps:
1. Let d be a Continuation that always returns its State argument as a successful MatchResult.
2. Call m(x, d) and let r be its result.
3. If r is failure, return failure.
4. Let y be r's State.
5. Let cap be y's captures internal array.
6. Let xe be x's endIndex.
7. Let z be the State (xe, cap).
8. Call c(z) and return its result.

I am currently working on building an executable version of the 
semantics of regular expression pattern matching, and I think I've found 
in a bug in how they are specified in both the released version of 
ECMA-262 and the latest working draft.

In §15.10.2.5, it says that:
The production Term :: Assertion evaluates by returning an internal 
Matcher closure that takes two arguments, a State x and a Continuation 
c, and performs the following:
1. Evaluate Assertion to obtain an AssertionTester t.
[ ... ]

However, the definition of the negative and positive lookahead 
assertions in §15.10.2.6 do not return AssertionTesters (like the ^, $, 
\b, and \B assertions do) but matchers:
The production Assertion :: ( ? = Disjunction ) evaluates as follows:
1. Evaluate Disjunction to obtain a Matcher m.
2. Return an internal Matcher closure that takes two arguments, a State 
x and a Continuation c, and performs the following steps:
    1. Let d be a Continuation that always returns its State argument as 
a successful MatchResult.
    2. Call m(x, d) and let r be its result.
    3. If r is failure, return failure.
    4. Let y be r's State.
    5. Let cap be y's captures internal array.
    6. Let xe be x's endIndex.
    7. Let z be the State (xe, cap).
    8. Call c(z) and return its result.

-- 
Joshua Cranmer