TITLE

DRAFT: Synopsis 32: Setting Library - Str

AUTHORS

Rod Adams <rod@rodadams.net>
Larry Wall <larry@wall.org>
Aaron Sherman <ajs@ajs.com>
Mark Stosberg <mark@summersault.com>
Carl Mäsak <cmasak@gmail.com>
Moritz Lenz <moritz@faui2k3.org>
Tim Nelson <wayland@wayland.id.au>

VERSION

Created: 19 Mar 2009 extracted from S29-functions.pod

Last Modified: 2012-07-24
Version: 9

The document is a draft.

If you read the HTML version, it is generated from the Pod in the specs repository under https://github.com/perl6/specs/blob/master/S32-setting-library/Str.pod so edit it there in the git repository if you would like to make changes.

Str

General notes about strings:

A Str can exist at several Unicode levels at once. Which level you interact with typically depends on what your current lexical context has declared the "working Unicode level to be". Default is Grapheme. [Default can't be CharLingua because we don't go into "language" mode unless there's a specific language declaration saying either exactly what language we're going into or, in the absence of that, how to find the exact language somewhere in the environment.]

Attempting to use a string at a level higher it can support is handled without warning. The current highest supported level of the string is simply mapped Char for Char to the new higher level. However, attempting to stuff something of a higher level a lower-level string is an error (for example, attempting to store Kanji in a Byte string). An explicit conversion function must be used to tell it how you want it encoded.

Attempting to use a string at a level lower than what it supports is not allowed.

If a function takes a Str and returns a Str, the returned Str will support the same levels as the input, unless specified otherwise.

The following are all provided by the Str role:

chop

multi method chop ( Str  $string: --> Str ) is export

Returns string with one Char removed from the end.

chomp

multi method chomp ( Str $string: --> Str ) is export

Returns string with one newline removed from the end. An arbitrary terminator can be removed if the input filehandle has marked the string for where the "newline" begins. (Presumably this is stored as a property of the string.) Otherwise a standard newline is removed.

Note: Most users should just let their I/O handles autochomp instead. (Autochomping is the default.)

lc

multi method lc ( Str $string: --> Str ) is export

Returns the input string after forcing each character to its lowercase form. Note that one-to-one mapping is not in general guaranteed; different forms may be chosen according to context.

uc

multi method uc ( Str $string: --> Str ) is export

Returns the input string after forcing each character to its uppercase (not titlecase) form. Note that one-to-one mapping is not in general guaranteed; different forms may be chosen according to context.

fc

multi method fc ( Str $string: --> Str ) is export

Does a Unicode "fold case" operation suitable for doing caseless string comparisons. (In general, the returned string is unlikely to be useful for any purpose other than comparison.)

tc

multi method tc ( Str $string: --> Str ) is export

Converts the first character of a string to titlecase form, leaving the rest of the characters unchanged, then returns the modified string. If there is no titlecase mapping for the first character, the entire string is returned unchanged. In any case, this function never changes any character after the first. (It is like the old ucfirst function in that respect.)

tclc

multi method tclc ( Str $string: --> Str ) is export

Forces the first character of a string to titlecase and the rest of the characters to lowercase, then returns the modified string.

tcuc

multi method tcuc ( Str $string: --> Str ) is export

Forces the first character of a string to titlecase and the rest of the characters to uppercase, then returns the modified string.

wordcase

multi method wordcase ( Str $string: :&filter = &tclc, :$where = True --> Str ) is export

Performs a substitutional mapping of each word in the string, defaulting to the tclc mapping. Words are defined as Perl 6 identifiers, hence admit hyphens and apostrophes when followed by a letter. (Note that trailing apostrophes don't matter when casemapping.) The following should have the same result:

.wordcase;
.subst(:g, / <ident>+ % <[ \- ' ]> /, *.Str.tclc)

The filter function is applied to the first and last word always, and to any intermediate word that the where parameter smartmatches. Assuming suitable definitions of word lists, standard English capitalization might be handled with something like this:

.wordcase(where => none @conjunctions, @prepositions);

(Note, "standard" authorities disagree on the prepositions!)

There is no provision for an alternate regex; if you need a custom word recognizer, you can write your own .subst as above.

normalize

multi method normalize ( Str $string: Bool :$canonical = Bool::True, Bool :$recompose = Bool::False --> Str ) is export

Performs a Unicode "normalization" operation on the string. This involves decomposing the string into its most basic combining elements, and potentially re-composing it. Full detail on the process of decomposing and re-composing strings in a normalized form is covered in the Unicode specification Sections 3.7, Decomposition and 3.11, Canonical Ordering Behavior of the Unicode Standard, 4.0. Additional named parameters are reserved for future Unicode expansion.

For everyday use there are aliases that map to the Unicode Standard Annex #15: Unicode Normalization Forms document's names for the various modes of normalization:

multi method nfd ( Str $string: --> Str ) is export {
  $string.normalize(:canonical, :!recompose);
}
multi method nfc ( Str $string: --> Str ) is export {
  $string.normalize(:canonical, :recompose);
}
multi method nfkd ( Str $string: --> Str ) is export {
  $string.normalize(:!canonical, :!recompose);
}
multi method nfkc ( Str $string: --> Str ) is export {
  $string.normalize(:!canonical, :recompose);
}

Decomposing a string can be used to compare Unicode strings in a binary form, providing that they use the same encoding. Without decomposing first, two Unicode strings may contain the same text, but not the same byte-for-byte data, even in the same encoding. The decomposition of a string is performed according to tables in the Unicode standard, and should be compatible with decompositions performed by any system.

The :canonical flag controls the use of "compatibility decompositions". For example, in canonical mode, "ï¬�" is left unaffected because it is not a composition. However, in compatibility mode, it will be replaced with "fi". Decomposed sequences will be ordered in a canonical way in either mode.

The :recompose flag controls the re-composition of decomposed forms. That is, a combining sequence will be re-composed into the canonical composite where possible.

These de-compositions and re-compositions are performed recursively, until there is no further work to be done.

Note that this function is really only applicable when dealing with codepoint strings. Grapheme strings are normally processed at a higher abstraction level that is independent of normalization, and are lazily normalized into the desired normalization when transferred to lexical scopes or handles that care.

samecase

multi method samecase ( Str $string: Str $pattern --> Str ) is export

Has the effect of making the case of the string match the case pattern in $pattern. (Used by s:ii/// internally, see S05.)

samemark

multi method samemark ( Str $string: Str $pattern --> Str ) is export

Has the effect of making the case of the string match the marking pattern in $pattern. (Used by s:mm/// internally, see S05.)

length

This word is banned in Perl 6. You must specify units.

chars

multi method chars ( Str $string: --> Int ) is export

Returns the number of characters in the string in the current (lexically scoped) idea of what a normal character is, usually graphemes.

graphs

multi method codes ( Str $string: --> Int ) is export

Returns the number of graphemes in the string in a language-independent way.

codes

multi method codes ( Str $string: $nf = $?NF --> Int ) is export

Returns the number of codepoints in the string as if it were canonicalized the specified way. Do not confuse codepoints with UTF-16 encoding. Characters above U+FFFF count as a single codepoint.

bytes

Gone. Use $str.encode($encoding).bytes instead.

encode

multi method encode($encoding = $?ENC, $nf = $?NF --> Buf )

Returns a Buf which represents the original string in the given encoding and normal form. The actual return type is as specific as possible, so $str.encode('UTF-8') returns a utf8 object, $str.encode('ISO-8859-1') a buf8.

index

multi method index( Str $string: Str $substring, StrPos $pos = StrPos(0) --> StrPos ) is export
multi method index( Str $string: Str $substring, Int $pos --> StrPos ) is export

index searches for the first occurrence of $substring in $string, starting at $pos. If $pos is an Int, it is taken to be in the units of the calling scope, which defaults to "graphemes".

The value returned is always a StrPos object. If the substring is found, then the StrPos represents the position of the first character of the substring. If the substring is not found, a bare StrPos containing no position is returned. This prototype StrPos evaluates to false because it's really a kind of undefined value. Do not evaluate as a number, because instead of returning -1 it will return 0 and issue a warning.

pack

multi pack( *@items where { all(@items) ~~ Pair } --> buf8 )
multi pack( Str $template, *@items --> buf8 )

pack takes a list of pairs and formats the values according to the specification of the keys. Alternately, it takes a string $template and formats the rest of its arguments according to the specifications in the template string. The result is a sequence of bytes.

Templates are strings of the form:

grammar Str::PackTemplate {
  regex TOP       { ^ <template> $ }
  regex template  { [ <group> | <specifier> <count>? ]* }
  token group     { \( <template> \) }
  token specifier { <[aAZbBhHcCsSiIlLnNvVqQjJfdFDpPuUwxX\@]> \!? }
  token count     { \*
                  | \[ [ \d+ | <specifier> ] \]
                  | \d+ }
}

In the pairwise mode, each key must contain a single <group> or <specifier>, and the values must be either scalar arguments or arrays.

[ Note: Need more documentation and need to figure out what Perl 5 things no longer make sense. Does Perl 6 need any extra formatting features? -ajs ]

[I think pack formats should be human readable but compiled to an internal form for efficiency. I also think that compact classes should be able to express their serialization in pack form if asked for it with .packformat or some such. -law]

quotemeta

multi method quotemeta ( Str $string: --> Str ) is export

Returns the input string with all non-"word" characters back-slashed. That is, all characters not matching "/<[A..Za..z_0..9]>/" will be preceded by a backslash in the returned string, regardless of any locale settings.

[Note from Pm: Should that be "/\w/" instead? Or, if the intent is to duplicate p5 functionality, perhaps it should be "p5quotemeta"? Do we even want this method at all?]

rindex

multi method rindex( Str $string: Str $substring, StrPos $pos? --> StrPos ) is export
multi method rindex( Str $string: Str $substring, Int $pos --> StrPos ) is export

Returns the position of the last $substring in $string. If $pos is specified, then the search starts at that location in $string, and works backwards. See index for more detail.

split

multi split ( Str $delimiter, Str $input, Int $limit = Inf --> List )
multi split ( Regex $delimiter, Str $input, Int $limit = Inf --> List )
multi method split ( Str $input: Str $delimiter, Int $limit = Inf --> List )
multi method split ( Str $input: Regex $delimiter, Int $limit = Inf, Bool :$all = False --> List )

Splits a string up into pieces based on delimiters found in the string.

String delimiters must not be treated as rules but as constants. The default is no longer ' ' since that would be interpreted as a constant. P5's split(' ') will translate to comb. Null trailing fields are no longer trimmed by default.

The split function no longer has a default delimiter nor a default invocant. In general you should use words to split on whitespace now, or comb to break into individual characters. See below.

If the :all adverb is supplied to the Regex form, then the delimiters are returned as Match objects in alternation with the split values. Unlike with Perl 5, if the delimiter contains multiple captures they are returned as submatches of single Match object. (And since Match does Capture, whether these Match objects eventually flatten or not depends on whether the expression is bound into a list or slice context.)

You may also split lists and filehandles. $*ARGS.split(/\n[\h*\n]+/) splits on paragraphs, for instance. Lists and filehandles are automatically fed through cat in order to pretend to be string. The resulting Cat is lazy. Accessing a filehandle as both a filehandle and as a Cat is undefined.

comb

multi comb ( Str $matcher, Str $input, Int $limit = Inf, Bool :$match --> List )
multi comb ( Regex $matcher, Str $input, Int $limit = Inf, Bool :$match --> List )
multi method comb ( Str $input: Str $matcher, Int $limit = Inf, Bool :$match --> List )
multi method comb ( Str $input: Regex $matcher = /./, Int $limit = Inf, Bool :$match --> List )

The comb function looks through a string for the interesting bits, ignoring the parts that don't match. In other words, it's a version of split where you specify what you want, not what you don't want.

That means the same restrictions apply to the matcher rule as do to split's delimiter rule.

By default it pulls out all individual characters. Saying

$string.comb(/pat/, $n)

is equivalent to

map {.Str}, $string.match(rx:global:x(0..$n):c/pat/)

You may also comb lists and filehandles. +$*IN.comb counts the characters on standard input, for instance. comb(/./, $thing) returns a list of single Char strings from anything that can give you a Str. Lists and filehandles are automatically fed through cat in order to pretend to be string. This Cat is also lazy.

If the :match adverb is applied, a list of Match objects (one per match) is returned instead of strings. This can be used to access capturing subrules in the matcher. The unmatched portions are never returned -- if you want that, use split :all. If the function is combing a lazy structure, the return values may also be lazy. (Strings are not lazy, however.)

lines

multi method lines ( Str $input: Int $limit = Inf --> List ) is export

Returns a list of lines, i.e. the same as a call to $input.comb( / ^^ \N* /, $limit ) would.

words

multi method words ( Str $input: Int $limit = Inf --> List ) is export

Returns a list of non-whitespace bits, i.e. the same as a call to $input.comb( / \S+ /, $limit ) would.

flip

The flip function reverses a string character by character.

multi method flip ( $str: --> Str ) is export {
   $str.comb.reverse.join;
}

This function will misplace accents if used at a Unicode level less than graphemes.

sprintf

multi method sprintf ( Str $format: *@args --> Str ) is export

This function is mostly identical to the C library sprintf function.

The $format is scanned for % characters. Any % introduces a format token. Format tokens have the following grammar:

grammar Str::SprintfFormat {
 regex format_token { '%': <index>? <precision>? <directive> }
 token index { \d+ '$' }
 token precision { <flags>? <vector>? <precision_count> }
 token flags { <[ \x20 + 0 \# \- ]>+ }
 token precision_count { [ <[1..9]>\d* | '*' ]? [ '.' [ \d* | '*' ] ]? }
 token vector { '*'? v }
 token directive { < % c s d u o x e f g X E G b p n i D U O F > }
}

Directives guide the use (if any) of the arguments. When a directive (other than %) is used, it indicates how the next argument passed is to be formatted into the string.

The directives are:

%   a literal percent sign
c   a character with the given codepoint
s   a string
d   an integer, in decimal
b   an integer, in binary
o   an integer, in octal
x   an integer, in hexadecimal
X   like x, but using uppercase letters
e   a floating-point number, in scientific notation
f   a floating-point number, in fixed decimal notation
g   a floating-point number, in %e or %f notation
E   like e, but using an uppercase "E"
G   like g, but with an uppercase "E" (if applicable)

Compatibility:

i   a synonym for %d
u   a synonum for %d
D   a synonym for %d
U   a synonym for %u
O   a synonym for %o
F   a synonym for %f

Perl 5 (non-)compatibility:

n   produces a runtime exception
p   produces a runtime exception

fmt

multi method fmt( Scalar $scalar: Str $format = '%s' --> Str )
multi method fmt( List $list:
                  Str $format = '%s',
                    Str $separator = ' '
                --> Str )
multi method fmt( Hash $hash:
                  Str $format = "%s\t%s",
                  Str $separator = "\n"
                --> Str )
multi method fmt( Pair $pair: Str $format = "%s\t%s" --> Str )

A set of wrappers around sprintf. A call to the scalar version $o.fmt($format) returns the result of sprintf($format, $o). A call to the list version @a.fmt($format, $sep) returns the result of join $sep, map { sprintf($format, $_) }, @a. A call to the hash version %h.fmt($format, $sep) returns the result of join $sep, map { sprintf($format, $_.key, $_.value) }, %h.pairs. A call to the pair version $p.fmt($format) returns the result of sprintf($format, $p.key, $p.value).

substr

multi method substr (Str $string: StrPos $start, StrLen $length? --> Str ) is export
multi method substr (Str $string: StrPos $start, StrPos $end --> Str ) is export
multi method substr (Str $string: StrPos $start, Int $length --> Str ) is export
multi method substr (Str $string: Int $start, StrLen $length? --> Str ) is export
multi method substr (Str $string: Int $start, StrPos $end --> Str ) is export
multi method substr (Str $string: Int $start, Int $length --> Str ) is export

substr returns part of an existing string. You control what part by passing a starting position and optionally either an end position or length. If you pass a number as either the position or length, then it will be used as the start or length with the assumption that you mean "chars" in the current Unicode abstraction level, which defaults to graphemes. A number in the 3rd argument is interpreted as a length rather than a position (just as in Perl 5).

Here is an example of its use:

$initials = substr($first_name,0,1) ~ substr($last_name,0,1);

The function fails if either the start position or length is negative or undefined. (If the length argument is not given, it defaults to the rest of the string.) Either of start position or end position may be specified relative to the end of the string using a WhateverCode whose argument will be the position of the end of the string. While it is illegal for the start position to be outside of the string, it is allowed for the final position to be off the end of the string; in this case the entire rest of the string is returned, whatever is available.

substr-rw

multi sub substr-rw($s is rw, $from = 0; $chars = $s.chars - $from) is rw

A version of substr that returns a writable reference to a part of a string variable:

$string ~~ /(barney)/;
substr-rw($string, $0.from, $0.to) = "fred";

trim

multi method trim() is export;

Returns a copy of the string, with leading and trailing whitespace removed.

unpack

match

method Match match(Str $self: Regex $search);

See "Substitution" in S05

subst

method Str subst(Str $self: Regex $search, Str $replacement);

trans

method trans(Str $self: Str $key, Str $val);

multi trans(List of Pair %data --> Any );

indent

multi method indent ($str: $steps --> Str ) is export;

Returns a re-indented string wherein $steps number of spaces have been added to each line. If a line already begins with horizontal whitespace, the new spaces are added to the end of those.

If the whitespace at the beginning of the line consists of only chr(32) spaces, chr(32) spaces are added as indentation as well. If the whitespace at the beginning of the line consists of some other kind of horizontal whitespace, that kind of whitespace is added as indentation. If the whitespace at the beginning of the line consists of two or more different kinds of horizontal whitespace, again chr(32) spaces are used.

If $steps is negative, removes that many spaces instead. Should any line contain too few leading spaces, only those are removed and a warning is issued. At most one such warning is issued per .indent call.

If $steps is *, removes just enough indentation to make some line have zero indentation.

The method will assume hard tabs to be equivalent to ($?TABSTOP // 8) spaces, and will treat any other horizontal whitespace character as equivalent to one chr(32) space. If the indenting doesn't "add up evenly", one hard tab needs to be exploded into the equivalent number of spaces before the unindenting of that line.

Decisions on how to indent each line are based solely on characters on that line. Thus, an .indent call on a multiline string therefore amounts to .lines».indent.join("\n") , modulo exotic line endings in the original string.

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