S29-functions.pod

TITLE

Synopsis 29: Builtin Functions

VERSION

Created: 12 Mar 2005

Last Modified: 24 April 2015
Version: 63

The document is a draft.

Notes

In Perl 6, all builtin functions belong to a named package (generally a class or role). Not all functions are guaranteed to be imported into the CORE scope. In addition, the list of functions imported into CORE will be subject to change with each release of Perl. Authors wishing to "Future Proof" their code should either specifically import the functions they will be using, or always refer to the functions by their full name.

After 6.0.0 comes out, global aliases will not be removed lightly, and will never be removed at all without having gone through a deprecation cycle of at least a year. In any event, you can specify that you want the interface for a particular version of Perl, and that can be emulated by later versions of Perl to the extent that security updates allow.

Where code is given here, it is intended to define semantics, not to dictate implementation.

Operators vs. Functions

There is no particular difference between an operator and a function, but for the sake of documentation, only functions declared without specifying a grammatical category or with a category of term: (see "Bits and Pieces" in S02) will be described as "functions", and everything else as "operators" which are outside of the scope of this document. (See S03 for operators.)

Multis vs. Functions

In actual fact, most of the "functions" defined here are multi subs, or are multi methods that are also exported as multi subs. The Setting is responsible for importing all the standard multi subs from their various packages into the CORE lexical scope. See S02.

Type Declarations

The following type declarations are assumed:

Matcher

subset Matcher of Mu where * !=== any(Bool,Match,Nil)

Used to supply a test to match against. Assume ~~ will be used against it. Booleans are forbidden because they almost always indicate a programming error where the argument has been evaluated too soon against the wrong $_. For instance:

grep $_ == 1, 1,2,3;        # evaluating wrong $_, so forbidden
grep { $_ == 1 }, 1,2,3;    # okay
grep * == 1, 1,2,3;         # okay

Ordering

subset KeyExtractor of Code where { .signature === :(Any --> Any) };
subset Comparator   of Code where { .signature === :(Any, Any --> Int ) };
subset OrderingPair of Pair where { .left ~~ KeyExtractor && .right ~~ Comparator };

subset Ordering where Signature | KeyExtractor | Comparator | OrderingPair | Whatever;

Used to handle comparisons between things. Generally this ends up in functions like sort(), min(), max(), etc., as a $by parameter which provides the information on how two things compare relative to each other.

Comparator

A closure with arity of 2, which for ordering returns negative/zero/positive, signaling the first argument should be before/tied with/after the second. aka "The Perl 5 way".

For equivalence the closure returns either not 0 or 0 indicating if the first argument is equivalent or not to the second.

KeyExtractor

A closure with arity of 1, which returns the "key" by which to compare. Values are compared using cmp for orderings and eqv for equivalences, which in Perl 6 do different comparisons depending on the types. (To get a Perl 5 string ordering you must compare with leg instead.)

Internally the result of the KeyExtractor on a value should be cached.

Note that it is very easy to generate a simple KeyExtractor using ~* for strings and +* for numbers, since with most simple operators * returns a closure of one argument.

@sorted = sort +*, @unsorted;  #ascending numeric
@sorted = sort -*, @unsorted;  #descending numeric

OrderingPair

A combination of the two methods above, for when one wishes to take advantage of the internal caching of keys that is expected to happen, but wishes to compare them with something other than eqv or cmp, such as <=> or leg.

Signature

If a signature is specified as a criterion, the signature is bound to each value and then each parameter does comparisons in positional order according to its type, as modified by its traits. Basically, the system will write the body of the key extraction and comparison subroutine for you based on the signature.

For ordering the list of positional parameter comparisons is reduced as if using [||] but all comparisons do not need to be performed if an early one determines an increasing or decreasing order. For equivalence the list is reduced as if using [&&].

Whatever

An ordering of * does the default comparison for the operator:

@sorted = sort *, @unsorted;

Function Packages

Context

caller

See "The callframe and caller functions" in S06.

callframe

See "The callframe and caller functions" in S06.

EVAL

macro EVAL ( Str|Buf $code, Grammar :$lang = CALLER::<$?PARSER>)

Execute $code as if it were code written in $lang. If $code is of type Buf, the same decoding techniques are applied as a compiler for $lang would usually do to input files.

The default for $lang is the language in effect at the exact location of the EVAL call.

Returns whatever $code returns, or fails when the compilation fails.

Note that unlike in Perl 5's eval, EVAL does not catch any exceptions or control exceptions.

EVALFILE

multi EVALFILE (Str $filename ; Grammar :$lang = Perl6)

Behaves like, and replaces Perl 5 do EXPR, with optional $lang support.

exit

multi exit (Int $status = 0)

Stops all program execution, and returns $status to the calling environment.

An exit runs all appropriate scope-leaving blocks such as LEAVE, KEEP, and UNDO, followed by all END blocks, followed by all DESTROYs that do more than just reclaim memory, and so cannot be skipped because they may have side effects visible outside the process. If run from an embedded interpreter, all memory must also be reclaimed.

Exit can also be called from an END block: in that case only the $status to be returned to the calling environment, is changed. This does end the execution of the END block in question, but will still execute any remaining END blocks.

Any threads started with the :app_lifetime parameter (which is basically any asynchronous action started with primitives other than Thread.new), will be terminated on exit.

sleep

multi sleep ( Real $for --> Nil )
multi sleep ( Whatever --> Nil )

Attempt to sleep for up to $for seconds, or forever when the argument is *. Implementations are obligated to support sub-second resolutions if that is at all possible. You may pass any of Int, Num, Rat, or Duration types as an argument, since those all do Real, but regardless of which type you use, they are always scaled to seconds. (An implementation is allowed to provide access to a platform-specific function based on, say, nanoseconds, but Perl 6 does not presume to know how much resolution clocks will have in the future, so requires everything to be specified in fractional seconds.)

This function returns nothing; use sleep-timer if you wish it to return how much time is remaining on the specified sleep. However, if you really just want to keep rolling over in bed until your alarm goes off at a particular time, use sleep-till instead, since it is not subject to relative clock drift.

All of these sleep functions work only on the current thread.

sleep-timer

multi sleep-timer ( Real $for --> Duration )

Just like sleep, but returns the amount of time remaining to sleep as a Duration (which will be 0 if the call was not interrupted). Depending on the platform and the system call involved, this may or may not require emulation by interrogating the clock before and after. For those systems whose system call returns the remaining time, this can be more efficient than interrogating the clock twice yourself, However, the optimizer is encouraged to change this to a bare sleep in sink context. (But then, you might as well just write that in the first place.)

sleep-till

multi sleep-till ( Instant $till --> Bool )

Just like sleep, but checks the current time and goes back to sleep if accidentally woken up early, to guarantee waiting until the specified time. Returns True if the function actually waited, or if the specified time happens to be the present moment. Returns False if you asked to sleep until a time in the past.

die

multi die (@LIST)

Throws a fatal Exception. The default exception handler prints each element of the list to $*ERR (STDERR).

fail

multi fail (Str $message)

Can only be called inside a routine and causes the routine to return an unthrown exception; a Failure object which stringifies to $message. If use fatal is in effect where the routine was called from, it throws the exception.

Conversions

bless

method bless(*@protos, *%init_args )

Calling bless on any invocant (but typically a type object) to create a new object with the same class as the invocant.

The .bless method takes the first positional argument indicating a candidate to bless. If absent, the object builder implicitly asks the representation what its preferred, er, representation is.

bless automatically creates an object appropriate to the representation of the class, then calls all appropriate BUILD routines for the current class, which initializes the object in least-derived to most-derived order. See "Objects" in S12 for more detailed information on object creation.

chrs

ords

chr

ord

multi sub chrs( Int *@grid  --> Str )
multi method ords( Str $string: --> List of Int ) is export
multi method chr( Int $grid: --> Str ) is export
multi method ord( Str $string: --> Int ) is export

chrs takes zero or more integer grapheme ids and returns the corresponding characters as a string. If any grapheme id is used that represents a higher abstraction level than the current lexical scope supports, that grapheme is converted to the corresponding lower-level string of codepoints/bytes that would be appropriate to the current pragmatic context, just as any other Str would be downgraded in context.

ords goes the other direction; it takes a string value and returns character values as integers. The definition of character is pragma dependent. Normally it's a grapheme id, but under codepoints or bytes scopes, the string is coerced to the appropriate low-level view and interpreted as codepoints or bytes. Hence, under "use bytes" you will never see a value larger than 256, and under "use codepoints" you will probably never see a value larger than 0x10ffff. The only guarantee under "use graphemes" (the default) is that the number returned will correspond to the codepoint of the precomposed codepoint representing the grapheme, if there is such a codepoint. Otherwise, the implementation is free to return any negative unique 32-bit id. (The chr function will know how to backtranslate such ids properly to codepoints or bytes in any context. Note that we are assuming that every codepoint's context knows its normalization preferences, and every byte's context also knows its encoding preferences. (These are knowable in the lexical scope via the $?NF and $?ENC compile-time constants).)

The chr and ord variants are restricted to processing a single character. As is customary, you may pass a longer string to ord, but only the first character will be translated.

item

multi item ( $item --> Item )

Forces generic Item context on its argument, and returns it.

list

multi list ( Iterable $item --> List ) { $item.iterator.list }
multi list ( List \iter --> List ) { iter }

Almost a no-op; just makes sure that $item can be iterated.

flat

multi flat ( *@list --> List )

Forces flat context on its arguments, and returns them. The heavy work is done by the *@ binding.

lol

multi lol ( **@list --> List )

Forces the argument list to be evaluated in lol ("list of lists") context. (Subscripts treat such a list of lists as a multidimensional slice.) Any sublist within the top level of the outer list will be transformed into an item (Scalar). The work is actually done by the binding to the **@ parameter. See also the more general .tree method, which defaults to itemizing every level.

hash

The hash contextualizer

multi hash ( *@list --> Hash )

Forces the argument list to be evaluated in hash context. The expression is evaluated in list context (flattening any Captures), then a hash will be created from the list, taken as a list of Pairs. (Any element in the list that is not a Pair will pretend to be a key and grab the next value in the list as its value.) Equivalent to %() (except that empty %() means %($/), while empty hash() means an empty hash).

gist

multi gist( |item --> Str )
multi method gist( Mu $item: --> Str )

Produces an informal string coercion, something a human might want to see if debugging, for instance. Each type may decide its own gist representation. Mu.gist just calls .perl, but any type's gist method may override this to remove metainfo that a human would find to be cluttery or redundant, or to format a composite value with suitable whitespace to tell the bits apart, or to trim down an infinite list to something slightly shorter.

gist is used as a last-ditch string coercion on each individual argument of various human-facing output routines, specifically say, note, warn, and any non-exceptional arguments to die. The print function is specifically excluded, since it's outputting to a printer. :-)

:16, :8, :2, :10

multi prefix:<:16> ( Str $hexstr --> Num )
multi prefix:<:8> ( Str $octstr --> Num )
multi prefix:<:2> ( Str $binstr --> Num )
multi prefix:<:10> ( Str $decstr --> Num )
etc.

Interprets string as a number, with a default hexadecimal/octal/binary/decimal radix. Any radix prefix (0b, 0d, 0x, 0o) mentioned inside the string will override this operator (this statement is true: 10 == :8("0d10")), except 0b and 0d will be interpreted as hex digits by :16 (hex("0d10") == :16 "0d10"). fails on failure.

These aren't really functions, syntactically, but adverbial forms that just happen to allow a parenthesize argument. But more typically you'll see

:4<222>
:16<deadbeef>

and such.

Replaces Perl 5 hex and oct.

OS

gethost

multi gethost( --> OS::Name )
multi gethost( Str $name, OS::Addfamily :$type --> OS::Name )
multi method gethost( OS::Addr $addr: --> OS::Name ) is export
multi method gethost( URI $uri: --> OS::Name ) is export

The gethost function operates on host naming or address information and returns an OS::Name. An OS::Name is, minimally:

class OS::Name {
  has Str $.name;
  has OS::Addr $.addr;
  has Array of Str @.aliases;
  has Array of OS::Addr @.addrs;
}

Such names can apply to anything which has a name that maps to an address, however, in this case the name is a hostname and the address is some sort of network identifier (e.g. an IPV4 address when resolving hosts that have IPV4 addresses).

When stringified, an OS::Name yields its name. When stringified, an OS::Addr yields its address in an appropriate text format (e.g. "10.1.2.3" for an IPV4 address).

The optional type adverb can be passed when resolving a hostname, and will filter the result to only those addresses that are of the appropriate address family. This feature may be supported by the underlying operating system, or Perl may emulate it.

Examples:

say "Connection from {$socket.peer.gethost}";
my $address = gethost("foo.example.com").addr;
my $hostname = gethost(:addr<"10.1.2.3">);

chroot

multi chroot ( Str $path = CALLER::<$_> --> Bool )

On POSIX systems, changes the process context of the current process such that the "root" directory becomes $path and all rooted paths (those that begin with a leading path separator) are relative to that path. For security reasons, many operating systems limit this functionality to the superuser. The return value will be true on success.

getlogin

multi getlogin ( --> Str )

Returns the username of the account running the program. This may not be as secure as using getpwuid on some platforms.

kill

multi kill ( OS::Signal $signal, Bool :$group, *@pids --> Bool )
multi method kill ( Proc::PID $pid: OS::Signal $signal?, Bool :$group --> Bool )

Sends the given $signal to the process(es) given and returns a boolean value indicating success (true) if all of the processes existed and were sent the signal and failure (false) if any of the processes did not exist or the signal could not be delivered to them.

The $signal can be initialized from an integer signal number or a string. Common signals are:

KILL - stop the process, do not allow it to exit gracefully
TERM - stop the process, allow it to exit gracefully
HUP  - Hangup, often used as a request to re-run from scratch
STOP - Pause execution
CONT - Continue after a STOP

Consult your operating system documentation for the full list of signal names and numbers. For compatibility, a signal name may be prefixed with "SIG".

The method form may omit the signal. In this case, the default signal is 'TERM'.

If the :group named parameter is passed, kill will attempt to send the signal to a process group rather than a single process. This functionality is platform-specific.

The special signal 0 can be sent which does not actually deliver a signal at all, and is used to determine if processes are still running:

say "Still running" if $proc.kill(0);

run

shell

multi shell ( $expression,   :$cwd = $CWD, :%env = %*ENV --> Proc )
multi run   ( *$cmd, *@args, :$cwd = $CWD, :%env = %*ENV --> Proc )

shell and run execute an external program, and return control to the caller once the program has exited.

shell goes through the system shell (cmd on windows, /bin/sh on Unixish systems), thus interpreting all the usual shell meta characters.

run treats the first argument as an executable name, and the rest of the positional arguments as command line arguments that are passed to the executable without any processing (except that it encodes Strings to buffers first, as does shell).

Both return a Proc object, which boolifies to True if the program had a successful exit and False otherwise. The status method on a Proc provides the exit code. If a False Proc is sunk, an exception will be thrown of type X::Proc::Unsuccessful.

If you want to execute an external program asynchronously (as in, not waiting for it to be finished), you will need Proc::Async, as specced in S17-concurrency.

runinstead

multi runinstead ( ; Str $path, *@args )
multi runinstead ( ; Str $command )

Identical to run except that it never returns. The executed program replaces the currently running program in memory.

syscall

Concurrency

There are higher-level models of concurrency management in Perl (see "Concurrency" in S17). These functions are simply the lowest level tools

fork

sub Processes::fork( --> Proc )

Creates a copy of the current process. Both processes return from fork. The original process returns the child process as a Proc object. The newly created process returns the parent process as a Proc object. As with any Proc object, the child process object numifies to the process ID (OS dependent integer). However, the parent process object numifies to 0 so that the child and parent can distinguish each other.

Typical usage would be:

if !defined(my $pid = fork) {
  die "Error calling fork: $!";
} elsif $pid == 0 {
  say "I am the new child!";
  exit 0;
} else {
  say "I am the parent of {+$pid}";
  wait();
}

wait

multi method wait( Proc $process: *%options --> Proc::Status )

multi wait ( Proc $process = -1, *%options --> Proc::Status )

Waits for a child process to terminate and returns the status object for the child. This status object will numify to the process ID of the child that exited.

Important Proc::Status methods:

.exit - Numeric exit value
.pid - Process ID
.signal - Signal number if any, otherwise 0

For historical reasons there is a .status method which is equal to:

($status.exit +< 8) +| $status.signal

If $process is supplied, then wait will only return when the given process has exited. Either a full Proc object can be passed, or just a numeric process ID. A -1 explicitly indicates that wait should return immediately if any child process exits.

When called in this way, the returned Proc::Status object will have a .pid of -1 (which is also what it numifies to) if there was no such process to wait for.

The named options include:

blocking

Defaults to true. If set to false, this forces wait to return immediately.

WNOHANG

Exists for historical compatibility. WNOHANG = 1> is identical to blocking = False>.

Pending Apocalypse

The following functions are classified by Apocalypse/Synopsis numbers.

A/S??: OS Interaction

chroot crypt getlogin /[get|set][pw|gr].*/ kill setpgrp setpriority times

... These are probably going to be part of POSIX, automatically imported to GLOBAL if the platform is the right one

Default Functions

These functions are exported into the default namespace

all -- see S32-setting-library/Containers.pod

any -- see S32-setting-library/Containers.pod

cat -- see S32-setting-library/Containers.pod

categorize -- see S32-setting-library/Containers.pod

classify -- see S32-setting-library/Containers.pod

defined -- see S32-setting-library/Basics.pod

grep -- see S32-setting-library/Containers.pod

first -- see S32-setting-library/Containers.pod

join -- see S32-setting-library/Containers.pod

keys -- see S32-setting-library/Containers.pod

kv -- see S32-setting-library/Containers.pod

map -- see S32-setting-library/Containers.pod

max -- see S32-setting-library/Containers.pod

min -- see S32-setting-library/Containers.pod

none -- see S32-setting-library/Containers.pod

one -- see S32-setting-library/Containers.pod

pairs -- see S32-setting-library/Containers.pod

pick -- see S32-setting-library/Containers.pod

print -- see S32-setting-library/IO.pod

printf -- see S32-setting-library/IO.pod

reduce -- see S32-setting-library/Containers.pod

reverse -- see S32-setting-library/Containers.pod

roundrobin -- see S32-setting-library/Containers.pod

say -- see S32-setting-library/IO.pod

shape -- see S32-setting-library/Containers.pod

sort -- see S32-setting-library/Containers.pod

srand -- see S32-setting-library/Numeric.pod

undefine -- see S32-setting-library/Basics.pod

uri -- see S32-setting-library/IO.pod

values -- see S32-setting-library/Containers.pod

warn -- see S32-setting-library/Any.pod

zip -- see S32-setting-library/Containers.pod

Non-default Functions

These functions which existed in Perl 5 still exist but are not part of the default namespace any more.

Container

The following functions can now be found in or replaced by something in the Container modules.

delete, exists, pop, push, shift, splice, unshift

Numeric

See "Numeric" in S32.

IO

The following functions can now be found in or replaced by something in the IO modules.

accept, bind, binmode, chdir, chmod, chown, close, closedir, connect eof, fcntl, fileno, flock, getc, getsockname, getsockopt, glob, ioctl, link, listen lstat, mkdir, open, opendir, pipe, print, printf, read, readdir, readline, readlink readpipe, recv, rename, rewinddir, rmdir, say, seek, seekdir, select, send, setsockopt shutdown, socket, socketpair, stat, symlink, sysopen, sysread, sysseek syswrite, tell, telldir, truncate, umask, unlink

Temporal

The following functions can now be found in or replaced by something in the Temporal modules.

gmtime, localtime, time

String

The following functions can now be found in or replaced by something in the String module.

chop, chomp, index, lc, pack, rindex, split, sprintf, substr, uc, ucfirst, unpack

Obsolete Functions

Some of these are obsoleted only as general functions, and are still available by using the right packages. Others are obsoleted in that they're keywords, rather than functions (these are in their own section, below).

%

$num1 % $num2

Does a floating point modulo operation, i.e. 5.5 % 1 == 0.5 and 5 % 2.5 == 0.

dbmopen, dbmclose

use DB_File;

dump

Dumped. Restoring from core dumps is in any event not very useful on modern virtual-memory operating systems. Startup acceleration should be accomplished using a precompiler of some kind (details will be very implementation specific), or a pre-forking daemon such as Perl 5's App::Persistent (which will be an external module when it is ported).

each

See .pairs() method, above.

endpwent, endgrent, endservent, endprotoent, endnetent, endhostent

The NameServices role in S16 covers most of these.

format, formline

See Exegesis 7.

getgrgid, getgrnam, getpwnam, getpwuid

The User and Group roles in S16 cover most of these.

getpwent, getgrent, getservent, getnetent, gethostent

The NameServices role in S16 covers most of these.

length()

This word is banned in Perl 6. You must specify units. In practice, this probably means you want Str.chars(), although it could be Str.bytes(), or even something else. See S32-setting-library/String for details.

lcfirst

Retired due to lack of use case

msgctl, msgget, msgrcv, msgsnd

See IPC::SysV

local

Replaced by temp which, unlike local, defaults to not changing the value.

lock

See "Concurrency" in S17. lock has been replaced by Lock.new and methods on the Lock object.

quotemeta

Because regex escaping metacharacters can easily be solved by quotes ("Simplified lexical parsing of patterns" in S05), and variables are not automatically interpolated ("Variable (non-)interpolation" in S05), quotemeta is no longer needed.

Shell escaping should be handled by passing arguments to run, or with code that speaks the language of a specific shell.

pos

There is no pos function in Perl 6 because that would not allow a string to be shared among threads. Generally you want to use $/.to for that now, or keep your own position variable as a lexical.

prototype

&func.meta.signature;
&func.^signature;

ref

There is no ref() any more, since it was almost always used to get the type name in Perl 5. If you really want the type name, you can use $var.WHAT.perl. If you really want P5 ref semantics, use Perl5::p5ref.

But if you're just wanting to test against a type, you're likely better off performing an isa or does or can, or just $var ~~ TYPE.

reset

Was there a good use for this?

semctl, semget, semop

See IPC::SysV;

setpwent, setgrent, setservent, setprotoent, setnetent, sethostent

The NameServices role in S16 covers most of these.

shmctl, shmget, shmread, shmwrite

See IPC::SysV;

study

Algorithm was too Anglo-centric. Could be brought back if generalized somehow.

tie, tied

These are replaced by container types. The compiler is free to assume that any lexical variable is never going to change its container type unless some representation is made to that effect in the declaration. Note: P5's tied() is roughly replaced by P6's variable().

XXX Examples?

my $foo is ....? is tie the meta operation on the container type for 'rebless' - macro tie ( $var, $class, *@args ) { CODE { variable($var).meta.rebless( $class, *@args ) } } )

endXXX

untie

See notes on "tie", above, but basically these are replaced with container classes.

vec

Should replace vec with declared buffer/array of bit, uint2, uint4, etc.

waitpid

wait can now be called with or without an optional process/pid.

write

See Exegesis 7.

Keywords

The following were listed in Perl 5's perlfunc, but should now be considered keywords rather than functions.

last, my, next, no, our, package, return, sub, use

Default Export Questions

Not sure whether these are exported by default or not. Also, many may no longer exist; if so, they should be entered in the "Obsolete" section.

Signal-related

alarm kill

OS or library related

chroot
crypt
getlogin
getpeername -- should this go on Pipe?

OS objects:

--Process
getpgrp
getppid
getpriority
setpgrp
setpriority

--Service
getservbyname
getservbyport

--Protocol
getprotobyname
getprotobynumber

--Network
getnetbyaddr
getnetbyname

--Host
gethostbyaddr
gethostbyname

Flow control

succeed proceed redo

Other

caller chr die do EVAL exec exit fork goto hex import int oct ord require scalar sleep state syscall system times utime wait

AUTHORS

Rod Adams <[email protected]>
Larry Wall <[email protected]>
Aaron Sherman <[email protected]>
Mark Stosberg <[email protected]>
Carl Mäsak <[email protected]>
Moritz Lenz <[email protected]>
Tim Nelson <[email protected]>
Carlin Bingham <[email protected]>
Elizabeth Mattijsen <[email protected]>
Brent Laabs <[email protected]>