sovrin / unitas

100%

master: 100%

Pull #1

github

refactor(combinators): drop attempt, document that backtracking is free

attempt claimed to "wrap a parser to handle backtracking on failure",
but it cannot: a Failure is { ok: false; error?: string }, with no field
to record a position, and combinators hand every alternative the same
input string they started with. sequence discards its local remaining
and returns a bare failure(). Since create is itself the identity
function, attempt(p) was one extra closure around p and nothing else.

It was not accidentally a no-op — it is un-implementable in this design
without changing the Failure type. Its own test, "should backtrack on
failure", only asserted that a failing parser fails, which holds for any
parser at all.

Keeping it as a documented no-op would be the worse option: someone
arriving from Parsec writes attempt(p) expecting it to change behaviour
and silently gets nothing. Remove it and explain the actual guarantee in
the README's core concepts, which is where they will look for try.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

202 of 202 branches covered (100.0%)

Branch coverage included in aggregate %.

7 of 7 new or added lines in 7 files covered. (100.0%)

636 of 636 relevant lines covered (100.0%)

32.67 hits per line