Unsafe unicode friendly encoding.

Like encodeUtf, except it crashes when the input contains surrogate chars. For sanitized input, this can be useful.

Like encodeUtf, except this mimics the behavior of the base library when doing filesystem operations (usually filepaths), which is:

1. on unix, uses shady PEP 383 style encoding (based on the current locale, but PEP 383 only works properly on UTF-8 encodings, so good luck)
2. on windows does permissive UTF-16 encoding, where coding errors generate Chars in the surrogate range

Looking up the locale requires IO. If you're not worried about calls to setFileSystemEncoding, then unsafePerformIO may be feasible (make sure to deeply evaluate the result to catch exceptions).

Converts back to a unicode codepoint (total).

Note that this uses the version from os-string, not filepath

O(n) Append a byte/word to the end of an OsString

O(n) cons is analogous to (:) for lists.

O(1) Extract the last element of an OsString, which must be finite and non-empty. An exception will be thrown in the case of an empty OsString.

This is a partial function, consider using unsnoc instead.

O(n) Extract the elements after the head of an OsString, which must be non-empty. An exception will be thrown in the case of an empty OsString.

This is a partial function, consider using uncons instead.

O(n) Extract the head and tail of an OsString, returning Nothing if it is empty.

O(1) Extract the first element of an OsString, which must be non-empty. An exception will be thrown in the case of an empty OsString.

This is a partial function, consider using uncons instead.

O(n) Return all the elements of an OsString except the last one. An exception will be thrown in the case of an empty OsString.

This is a partial function, consider using unsnoc instead.

O(n) Extract the init and last of an OsString, returning Nothing if it is empty.

O(1) Test whether an OsString is empty.

O(1) The length of an OsString.

This returns the number of code units (Word8 on unix and Word16 on windows), not bytes.

O(1) The length in bytes of an OsString.

This always returns the number of bytes, regardless of which platform you're on.

O(n) map f xs is the OsString obtained by applying f to each element of xs.

O(n) reverse xs efficiently returns the elements of xs in reverse order.

O(n) The intercalate function takes an OsString and a list of OsStrings and concatenates the list after interspersing the first argument between each element of the list.

foldl, applied to a binary operator, a starting value (typically the left-identity of the operator), and an OsString, reduces the OsString using the binary operator, from left to right.

foldl' is like foldl, but strict in the accumulator.

foldl1 is a variant of foldl that has no starting value argument, and thus must be applied to non-empty OsStrings. An exception will be thrown in the case of an empty OsString.

foldl1' is like foldl1, but strict in the accumulator. An exception will be thrown in the case of an empty OsString.

foldr, applied to a binary operator, a starting value (typically the right-identity of the operator), and an OsString, reduces the OsString using the binary operator, from right to left.

foldr' is like foldr, but strict in the accumulator.

foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty OsStrings An exception will be thrown in the case of an empty OsString.

foldr1' is a variant of foldr1, but is strict in the accumulator.

O(n) Applied to a predicate and an OsString, all determines if all elements of the OsString satisfy the predicate.

O(n) Applied to a predicate and an OsString, any determines if any element of the OsString satisfies the predicate.

O(n) replicate n x is an OsString of length n with x the value of every element. The following holds:

replicate w c = unfoldr w (\u -> Just (u,u)) c

O(n), where n is the length of the result. The unfoldr function is analogous to the List 'unfoldr'. unfoldr builds a OsString from a seed value. The function takes the element and returns Nothing if it is done producing the OsString or returns Just (a,b), in which case, a is the next byte in the string, and b is the seed value for further production.

This function is not efficient/safe. It will build a list of [Word8] and run the generator until it returns Nothing, otherwise recurse infinitely, then finally create an OsString.

If you know the maximum length, consider using unfoldrN.

Examples:

   unfoldr (\x -> if x <= 5 then Just (x, x + 1) else Nothing) 0
== pack [0, 1, 2, 3, 4, 5]

O(n) Like unfoldr, unfoldrN builds an OsString from a seed value. However, the length of the result is limited by the first argument to unfoldrN. This function is more efficient than unfoldr when the maximum length of the result is known.

The following equation relates unfoldrN and unfoldr:

fst (unfoldrN n f s) == take n (unfoldr f s)

O(n) take n, applied to an OsString xs, returns the prefix of xs of length n, or xs itself if n > length xs.

O(n) takeEnd n xs is equivalent to drop (length xs - n) xs. Takes n elements from end of bytestring.

>>> takeEnd 3 "abcdefg"
"efg"
>>> takeEnd 0 "abcdefg"
""
>>> takeEnd 4 "abc"
"abc"

Returns the longest (possibly empty) suffix of elements satisfying the predicate.

takeWhileEnd p is equivalent to reverse . takeWhile p . reverse.

Similar to takeWhile, returns the longest (possibly empty) prefix of elements satisfying the predicate.

O(n) drop n xs returns the suffix of xs after the first n elements, or empty if n > length xs.

O(n) dropEnd n xs is equivalent to take (length xs - n) xs. Drops n elements from end of bytestring.

>>> dropEnd 3 "abcdefg"
"abcd"
>>> dropEnd 0 "abcdefg"
"abcdefg"
>>> dropEnd 4 "abc"
""

Similar to dropWhileEnd, drops the longest (possibly empty) suffix of elements satisfying the predicate and returns the remainder.

dropWhileEnd p is equivalent to reverse . dropWhile p . reverse.

Similar to dropWhile, drops the longest (possibly empty) prefix of elements satisfying the predicate and returns the remainder.

Similar to break, returns the longest (possibly empty) prefix of elements which do not satisfy the predicate and the remainder of the string.

break p is equivalent to span (not . p) and to (takeWhile (not . p) &&& dropWhile (not . p)).

Returns the longest (possibly empty) suffix of elements which do not satisfy the predicate and the remainder of the string.

breakEnd p is equivalent to spanEnd (not . p) and to (takeWhileEnd (not . p) &&& dropWhileEnd (not . p)).

Similar to span, returns the longest (possibly empty) prefix of elements satisfying the predicate and the remainder of the string.

span p is equivalent to break (not . p) and to (takeWhile p &&& dropWhile p).

Returns the longest (possibly empty) suffix of elements satisfying the predicate and the remainder of the string.

spanEnd p is equivalent to breakEnd (not . p) and to (takeWhileEnd p &&& dropWhileEnd p).

We have

spanEnd (not . isSpace) "x y z" == ("x y ", "z")

and

spanEnd (not . isSpace) sbs
   ==
let (x, y) = span (not . isSpace) (reverse sbs) in (reverse y, reverse x)

O(n) splitAt n sbs is equivalent to (take n sbs, drop n sbs).

O(n) Break an OsString into pieces separated by the byte argument, consuming the delimiter. I.e.

split 10  "a\nb\nd\ne" == ["a","b","d","e"]   -- fromEnum '\n' == 10
split 97  "aXaXaXa"    == ["","X","X","X",""] -- fromEnum 'a' == 97
split 120 "x"          == ["",""]             -- fromEnum 'x' == 120
split undefined ""     == []                  -- and not [""]

and

intercalate [c] . split c == id
split == splitWith . (==)

O(n) Splits an OsString into components delimited by separators, where the predicate returns True for a separator element. The resulting components do not contain the separators. Two adjacent separators result in an empty component in the output. eg.

splitWith (==97) "aabbaca" == ["","","bb","c",""] -- fromEnum 'a' == 97
splitWith undefined ""     == []                  -- and not [""]

O(n) The stripSuffix function takes two OsStrings and returns Just the remainder of the second iff the first is its suffix, and otherwise Nothing.

O(n) The stripPrefix function takes two OsStrings and returns Just the remainder of the second iff the first is its prefix, and otherwise Nothing.

Check whether one string is a substring of another.

O(n) The isPrefixOf function takes two OsStrings and returns True

O(n) The isSuffixOf function takes two OsStrings and returns True iff the first is a suffix of the second.

The following holds:

isSuffixOf x y == reverse x `isPrefixOf` reverse y

Break a string on a substring, returning a pair of the part of the string prior to the match, and the rest of the string.

The following relationships hold:

break (== c) l == breakSubstring (singleton c) l

For example, to tokenise a string, dropping delimiters:

tokenise x y = h : if null t then [] else tokenise x (drop (length x) t)
    where (h,t) = breakSubstring x y

To skip to the first occurrence of a string:

snd (breakSubstring x y)

To take the parts of a string before a delimiter:

fst (breakSubstring x y)

Note that calling `breakSubstring x` does some preprocessing work, so you should avoid unnecessarily duplicating breakSubstring calls with the same pattern.

O(n) elem is the OsString membership predicate.

O(n) The find function takes a predicate and an OsString, and returns the first element in matching the predicate, or Nothing if there is no such element.

find f p = case findIndex f p of Just n -> Just (p ! n) ; _ -> Nothing

O(n) filter, applied to a predicate and an OsString, returns an OsString containing those characters that satisfy the predicate.

O(n) The partition function takes a predicate an OsString and returns the pair of OsStrings with elements which do and do not satisfy the predicate, respectively; i.e.,

partition p bs == (filter p sbs, filter (not . p) sbs)

O(1) OsString index (subscript) operator, starting from 0.

O(1) OsString index, starting from 0, that returns Just if:

0 <= n < length bs

O(1) OsString index, starting from 0, that returns Just if:

0 <= n < length bs

O(n) The elemIndex function returns the index of the first element in the given OsString which is equal to the query element, or Nothing if there is no such element.

O(n) The elemIndices function extends elemIndex, by returning the indices of all elements equal to the query element, in ascending order.

count returns the number of times its argument appears in the OsString

O(n) The findIndex function takes a predicate and an OsString and returns the index of the first element in the OsString satisfying the predicate.

O(n) The findIndices function extends findIndex, by returning the indices of all elements satisfying the predicate, in ascending order.

This is a type-level evidence that OsChar is a newtype wrapper over WindowsChar or PosixChar and OsString is a newtype wrapper over WindowsString or PosixString. If you pattern match on coercionToPlatformTypes, GHC will know that relevant types are coercible to each other. This helps to avoid CPP in certain scenarios.

Note: normally, this requires os-string >= 2.0.2, but since it's required in the test suite, I've defined it here for os-string-2.0.1 and for older versions of filepath.