[elycruz]

Closes #152. Compares every exported fjl method that has a Haskell counterpart against base-4.22.0.0, and fixes the differences that weren't deliberate. The full inventory is in md/issues/HASKELL_PARITY.md, and every breaking change is in md/MIGRATION_V2.md.

GHC wasn't available, so expected values come from the examples and laws in the pinned docs, not from running Haskell.

Rules applied

• Match Haskell's results, result order and empty-input behaviour, but keep native and fjl argument and callback order, so foldr stays op(acc, x, i, xs).
• Value searches take the list last, including the ones that wrap native methods.
• A method that returns a variation of its list returns the list when nothing changes, so stripPrefix keeps returning it rather than undefined.

Breaking changes

Most of these change results without throwing, so they're listed under "Check these first" in the migration notes.

Method	Before	After
elem, notElem, elemIndex, includes, indexOf, lastIndexOf, and their $ forms	(xs, x)	(x, xs)
scanr, scanr1	fn(x, acc, i, xs)	fn(acc, x, i, xs), like foldr
repeat, cycle, iterate, replicateIter, unfoldrIter	Yielded growing lists	Yield items: take(3, repeat(17)) gives [17, 17, 17]
cycle([])	Yielded [] forever	Throws on first pull
take	Pulled n + 1 items	Pulls exactly n
mapAccumR	Reversed its result list	Keeps input order
groupBy	Compared with the previous item	Compares with the group's first item
nubBy	pred(item, kept)	pred(kept, item)
splitAt	A negative position counted from the end	[[], xs]
intercalate(',', [])	[]	''
lines	lines('one\n') gave ['one', '']	['one'], and lines('') gives []
words	Split on each space or tab	Splits on runs of whitespace, and ignores it at the ends
unlines	'a\nb'	'a\nb\n'
unionBy	pred(accumulatedList, x)	eq(a, b)
union	NaN equalled itself	Compares with ===
difference	Removed every occurrence	Removes one per item, so (xs ++ ys) \\ xs == ys holds
nub, nubBy, union, unionBy, intersect, intersectBy, difference	Gave an array or threw for strings	Give a string

Bugs fixed

• replicate threw on a negative count.
• concat([]) returned undefined.
• remove, removeBy and removeFirstsBy couldn't match a surrogate pair in a string.
• fjl-validator's defaultValueObscurer returned "*,*,*,**,*,*,**,*,*,*" for 'abc', and now gives "***". No test checked its output, so this adds one.

Worth checking

• Old-order calls often fail silently: includes(xs, 'a') with a string as xs checks whether 'a' contains that string and returns false.
• lines: still counts \r, \r\n and \n\r as one line break, as its doc comment promised. Haskell would keep the \r.
• complement: has no counterpart, so it still removes every occurrence, unlike difference.
• Deliberate differences: doc comments cover the ones v2.0 - Check Haskell parity for methods with Haskell counterparts #152 names, and the findings tables cover the rest.

Follow-ups

• fix(fjl): return strings for string input when a list method changes nothing #154: return strings for string input in take, filter, map and others.
• feat(fjl): accept generators wherever Haskell permits an infinite list #155: accept generators wherever Haskell permits an infinite list.

Testing

All 1,632 tests pass, and the build and lint have no errors. tsc still reports errors in fjl-labs and in fjl-validator-recaptcha's tests, neither of which this changes. New tests check the documented examples and laws where the docs give them.

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