Webb.String.CodePoint

type WCodePoint = CodePoint

newtype CodePoint

CodePoint is an Int bounded between 0 and 0x10FFFF, corresponding to Unicode code points.

Instances

• Eq CodePoint
• Ord CodePoint
• Show CodePoint
• Bounded CodePoint
• Enum CodePoint
• BoundedEnum CodePoint

uncons :: String -> Maybe { head :: CodePoint, tail :: String }

Returns a record with the first code point and the remaining code points of the string. Returns Nothing if the string is empty. Operates in constant space and time.

>>> uncons "𝐀𝐀 c 𝐀"
Just { head: CodePoint 0x1D400, tail: "𝐀 c 𝐀" }
>>> uncons ""
Nothing

toCodePointArray :: String -> Array CodePoint

Creates an array of code points from a string. Operates in space and time linear to the length of the string.

>>> codePointArray = toCodePointArray "b 𝐀𝐀"
>>> codePointArray
[CodePoint 0x62, CodePoint 0x20, CodePoint 0x1D400, CodePoint 0x1D400]
>>> map singleton codePointArray
["b", " ", "𝐀", "𝐀"]

takeWhile :: (CodePoint -> Boolean) -> String -> String

Returns a string containing the leading sequence of code points which all match the given predicate from the string. Operates in constant space and in time linear to the length of the string.

>>> takeWhile (\c -> fromEnum c == 0x1D400) "𝐀𝐀 b c 𝐀"
"𝐀𝐀"

take :: Int -> String -> String

Returns a string containing the given number of code points from the beginning of the given string. If the string does not have that many code points, returns the empty string. Operates in constant space and in time linear to the given number.

>>> take 3 "b 𝐀𝐀 c 𝐀"
"b 𝐀"
-- compare to Data.String:
>>> take 3 "b 𝐀𝐀 c 𝐀"
"b �"

stripSuffix :: Pattern -> String -> Maybe String

If the string ends with the given suffix, return the portion of the string left after removing it, as a Just value. Otherwise, return Nothing.

stripSuffix (Pattern ".exe") "psc.exe" == Just "psc"
stripSuffix (Pattern ".exe") "psc" == Nothing

stripPrefix :: Pattern -> String -> Maybe String

If the string starts with the given prefix, return the portion of the string left after removing it, as a Just value. Otherwise, return Nothing.

stripPrefix (Pattern "http:") "http://purescript.org" == Just "//purescript.org"
stripPrefix (Pattern "http:") "https://purescript.org" == Nothing

splitAt :: Int -> String -> { after :: String, before :: String }

Splits a string into two substrings, where before contains the code points up to (but not including) the given index, and after contains the rest of the string, from that index on.

>>> splitAt 3 "b 𝐀𝐀 c 𝐀"
{ before: "b 𝐀", after: "𝐀 c 𝐀" }

Thus the length of (splitAt i s).before will equal either i or length s, if that is shorter. (Or if i is negative the length will be 0.)

In code:

length (splitAt i s).before == min (max i 0) (length s)
(splitAt i s).before <> (splitAt i s).after == s
splitAt i s == {before: take i s, after: drop i s}

singleton :: CodePoint -> String

Creates a string containing just the given code point. Operates in constant space and time.

>>> map singleton (toEnum 0x1D400)
Just "𝐀"

length :: String -> Int

Returns the number of code points in the string. Operates in constant space and in time linear to the length of the string.

>>> length "b 𝐀𝐀 c 𝐀"
8
-- compare to Data.String:
>>> length "b 𝐀𝐀 c 𝐀"
11

lastIndexOf' :: Pattern -> Int -> String -> Maybe Int

Returns the number of code points preceding the first match of the given pattern in the string. Pattern matches following the given index will be ignored.

Giving a negative index is equivalent to giving 0 and giving an index greater than the number of code points in the string is equivalent to searching in the whole string.

Returns Nothing when no matches are found.

>>> lastIndexOf' (Pattern "𝐀") (-1) "b 𝐀𝐀 c 𝐀"
Nothing
>>> lastIndexOf' (Pattern "𝐀") 0 "b 𝐀𝐀 c 𝐀"
Nothing
>>> lastIndexOf' (Pattern "𝐀") 5 "b 𝐀𝐀 c 𝐀"
Just 3
>>> lastIndexOf' (Pattern "𝐀") 8 "b 𝐀𝐀 c 𝐀"
Just 7
>>> lastIndexOf' (Pattern "o") 5 "b 𝐀𝐀 c 𝐀"
Nothing

lastIndexOf :: Pattern -> String -> Maybe Int

Returns the number of code points preceding the last match of the given pattern in the string. Returns Nothing when no matches are found.

>>> lastIndexOf (Pattern "𝐀") "b 𝐀𝐀 c 𝐀"
Just 7
>>> lastIndexOf (Pattern "o") "b 𝐀𝐀 c 𝐀"
Nothing

indexOf' :: Pattern -> Int -> String -> Maybe Int

Returns the number of code points preceding the first match of the given pattern in the string. Pattern matches preceding the given index will be ignored. Returns Nothing when no matches are found.

>>> indexOf' (Pattern "𝐀") 4 "b 𝐀𝐀 c 𝐀"
Just 7
>>> indexOf' (Pattern "o") 4 "b 𝐀𝐀 c 𝐀"
Nothing

indexOf :: Pattern -> String -> Maybe Int

Returns the number of code points preceding the first match of the given pattern in the string. Returns Nothing when no matches are found.

>>> indexOf (Pattern "𝐀") "b 𝐀𝐀 c 𝐀"
Just 2
>>> indexOf (Pattern "o") "b 𝐀𝐀 c 𝐀"
Nothing

fromCodePointArray :: Array CodePoint -> String

Creates a string from an array of code points. Operates in space and time linear to the length of the array.

>>> codePointArray = toCodePointArray "c 𝐀"
>>> codePointArray
[CodePoint 0x63, CodePoint 0x20, CodePoint 0x1D400]
>>> fromCodePointArray codePointArray
"c 𝐀"

dropWhile :: (CodePoint -> Boolean) -> String -> String

Drops the leading sequence of code points which all match the given predicate from the string. Operates in constant space and in time linear to the length of the string.

>>> dropWhile (\c -> fromEnum c == 0x1D400) "𝐀𝐀 b c 𝐀"
" b c 𝐀"

drop :: Int -> String -> String

Drops the given number of code points from the beginning of the string. If the string does not have that many code points, returns the empty string. Operates in constant space and in time linear to the given number.

>>> drop 5 "𝐀𝐀 b c"
"c"
-- compared to Data.String:
>>> drop 5 "𝐀𝐀 b c"
"b c" -- because "𝐀" occupies 2 code units

countPrefix :: (CodePoint -> Boolean) -> String -> Int

Returns the number of code points in the leading sequence of code points which all match the given predicate. Operates in constant space and in time linear to the length of the string.

>>> countPrefix (\c -> fromEnum c == 0x1D400) "𝐀𝐀 b c 𝐀"
2

contains :: Pattern -> String -> Boolean

Checks whether the pattern appears in the given string.

contains (Pattern "needle") "haystack with needle" == true
contains (Pattern "needle") "haystack" == false

codePointFromChar :: Char -> CodePoint

Creates a CodePoint from a given Char.

>>> codePointFromChar 'B'
CodePoint 0x42 -- represents 'B'

codePointAt :: Int -> String -> Maybe CodePoint

Returns the first code point of the string after dropping the given number of code points from the beginning, if there is such a code point. Operates in constant space and in time linear to the given index.

>>> codePointAt 1 "𝐀𝐀𝐀𝐀"
Just (CodePoint 0x1D400) -- represents "𝐀"
-- compare to Data.String:
>>> charAt 1 "𝐀𝐀𝐀𝐀"
Just '�'