System.OsString.Internal

Partial unicode friendly encoding.

On windows this encodes as UTF16-LE (strictly), which is a pretty good guess. On unix this encodes as UTF8 (strictly), which is a good guess.

Throws an EncodingException if encoding fails. If the input does not contain surrogate chars, you can use unsafeEncodeUtf.

Unsafe unicode friendly encoding.

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

Encode a FilePath with the specified encoding.

Note: on windows, we expect a "wide char" encoding (e.g. UCS-2 or UTF-16). Anything that works with Word16 boundaries. Picking an incompatible encoding may crash filepath operations.

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).

Like encodeUtf, except this mimics the behavior of the base library when doing string operations, which is:

1. on unix this uses getLocaleEncoding

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).

Partial unicode friendly decoding.

On windows this decodes as UTF16-LE (strictly), which is a pretty good guess. On unix this decodes as UTF8 (strictly), which is a good guess. Note that filenames on unix are encoding agnostic char arrays.

Throws a EncodingException if decoding fails.

Decode an OsString with the specified encoding.

The String is forced into memory to catch all exceptions.

Like decodeUtf, 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).

Like decodeUtf, except this mimics the behavior of the base library when doing string operations, which is:

1. on unix this uses getLocaleEncoding

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).

Constructs an OsString from a ByteString.

On windows, this ensures valid UCS-2LE, on unix it is passed unchanged/unchecked.

Throws EncodingException on invalid UCS-2LE on windows (although unlikely).

QuasiQuote an OsString. This accepts Unicode characters and encodes as UTF-8 on unix and UTF-16 on windows. If used as pattern, requires turning on the ViewPatterns extension.

Unpack an OsString to a list of OsChar.

Pack a list of OsChar to an OsString

Note that using this in conjunction with unsafeFromChar to convert from [Char] to OsString is probably not what you want, because it will truncate unicode code points.

Truncates on unix to 1 and on Windows to 2 octets.

Converts back to a unicode codepoint (total).

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

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

O(1) Extract the last element of a 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 a 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 a OsString, returning Nothing if it is empty.

O(1) Extract the first element of a 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 a 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 a OsString, returning Nothing if it is empty.

O(1) Test whether a OsString is empty.

O(1) The length of a OsString.

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 a 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 a 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 a 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 a OsString, all determines if all elements of the OsString satisfy the predicate.

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

O(n) replicate n x is a 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 a 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 a 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 a 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 dropWhile, drops the longest (possibly empty) prefix of elements satisfying the predicate and returns the remainder.

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.

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 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)).

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 a 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 a 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 a 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 a OsString, returns a OsString containing those characters that satisfy the predicate.

O(n) The partition function takes a predicate a 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 a 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.