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#############################################################################
##
## This file is part of GAP, a system for computational discrete algebra.
## This file's authors include Thomas Breuer, Frank Celler.
##
## Copyright of GAP belongs to its developers, whose names are too numerous
## to list here. Please refer to the COPYRIGHT file for details.
##
## SPDX-License-Identifier: GPL-2.0-or-later
##
## This file deals with strings and characters.
##
#############################################################################
##
#C IsChar( <obj> ) . . . . . . . . . . . . . . . . . category of characters
#C IsCharCollection( <obj> ) . . . . . category of collections of characters
##
## <#GAPDoc Label="IsChar">
## <ManSection>
## <Filt Name="IsChar" Arg='obj' Type='Category'/>
## <Filt Name="IsCharCollection" Arg='obj' Type='Category'/>
##
## <Description>
## A <E>character</E> is simply an object in &GAP; that represents an
## arbitrary character from the character set of the operating system.
## Character literals can be entered in &GAP; by enclosing the character
## in <E>singlequotes</E> <C>'</C>.
## <Example><![CDATA[
## gap> x:= 'a'; IsChar( x );
## 'a'
## true
## gap> '*';
## '*'
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareCategory( "IsChar", IS_OBJECT );
DeclareCategoryCollections( "IsChar" );
#############################################################################
##
#C IsString( <obj> ) . . . . . . . . . . . . . . . . . . category of strings
##
## <#GAPDoc Label="IsString">
## <ManSection>
## <Filt Name="IsString" Arg='obj'/>
##
## <Description>
## A <E>string</E> is a dense list (see <Ref Filt="IsList"/>,
## <Ref Filt="IsDenseList"/>) of characters (see <Ref Filt="IsChar"/>);
## thus strings are always homogeneous
## (see <Ref Filt="IsHomogeneousList"/>).
## <P/>
## A string literal can either be entered as the list of characters
## or by writing the characters between <E>doublequotes</E> <C>"</C>.
## &GAP; will always output strings in the latter format.
## However, the input via the double quote syntax enables &GAP; to store
## the string in an efficient compact internal representation.
## See <Ref Filt="IsStringRep"/> below for more details.
## <P/>
## Each character, in particular those which cannot be typed directly from
## the keyboard, can also be typed in three digit octal notation, or
## two digit hexadecimal notation.
## And for some special characters (like the newline character) there is a
## further possibility to type them,
## see section <Ref Sect="Special Characters"/>.
## <P/>
## <Example><![CDATA[
## gap> s1 := ['H','e','l','l','o',' ','w','o','r','l','d','.'];
## "Hello world."
## gap> IsString( s1 );
## true
## gap> s2 := "Hello world.";
## "Hello world."
## gap> s1 = s2;
## true
## gap> s3 := ""; # the empty string
## ""
## gap> s3 = [];
## true
## gap> IsString( [] );
## true
## gap> IsString( "123" ); IsString( 123 );
## true
## false
## gap> IsString( [ '1', '2', '3' ] );
## true
## gap> IsString( [ '1', '2', , '4' ] ); # strings must be dense
## false
## gap> IsString( [ '1', '2', 3 ] ); # strings must only contain characters
## false
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareCategoryKernel( "IsString", IsHomogeneousList, IS_STRING );
InstallTrueMethod( IsString, IsCharCollection and IsList );
#############################################################################
##
#R IsStringRep( <obj> )
##
## <#GAPDoc Label="IsStringRep">
## <ManSection>
## <Filt Name="IsStringRep" Arg='obj' Type='Representation'/>
##
## <Description>
## <Ref Filt="IsStringRep"/> is a special (internal) representation of dense
## lists of characters.
## Dense lists of characters can be converted into this representation
## using <Ref Func="ConvertToStringRep"/>.
## Note that calling <Ref Filt="IsString"/> does <E>not</E> change the
## representation.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareRepresentationKernel( "IsStringRep",
IsInternalRep, IS_STRING_REP );
#############################################################################
##
#F ConvertToStringRep( <obj> ) . . . . . . . . . . . . . inplace conversion
##
## <#GAPDoc Label="ConvertToStringRep">
## <ManSection>
## <Func Name="ConvertToStringRep" Arg='obj'/>
##
## <Description>
## If <A>obj</A> is a dense internally represented list of characters then
## <Ref Func="ConvertToStringRep"/> changes the representation to
## <Ref Filt="IsStringRep"/>.
## This is useful in particular for converting the empty list <C>[]</C>,
## which usually is in <Ref Filt="IsPlistRep"/>,
## to <Ref Filt="IsStringRep"/>.
## If <A>obj</A> is not a string then <Ref Func="ConvertToStringRep"/>
## signals an error.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
BIND_GLOBAL( "ConvertToStringRep", CONV_STRING );
#############################################################################
##
#F CopyToStringRep( <obj> ) . . . . . . . . . . . . . . . copy conversion
##
## <#GAPDoc Label="CopyToStringRep">
## <ManSection>
## <Func Name="CopyToStringRep" Arg='obj'/>
##
## <Description>
## If <A>obj</A> is a dense internally represented list of characters then
## <Ref Func="CopyToStringRep"/> copies <A>obj</A> to a new object with
## representation
## <Ref Filt="IsStringRep"/>.
## If <A>obj</A> is not a string then <Ref Func="CopyToStringRep"/>
## signals an error.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
BIND_GLOBAL( "CopyToStringRep", COPY_TO_STRING_REP );
#############################################################################
##
#V CharsFamily . . . . . . . . . . . . . . . . . . . . family of characters
##
## <#GAPDoc Label="CharsFamily">
## <ManSection>
## <Fam Name="CharsFamily"/>
##
## <Description>
## Each character lies in the family <Ref Fam="CharsFamily"/>,
## each nonempty string lies in the collections family of this family.
## Note the subtle differences between the empty list <C>[]</C> and the
## empty string <C>""</C> when both are printed.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
BIND_GLOBAL( "CharsFamily", NewFamily( "CharsFamily", IsChar ) );
#############################################################################
##
#V TYPE_CHAR . . . . . . . . . . . . . . . . . . . . . . type of a character
##
## <ManSection>
## <Var Name="TYPE_CHAR"/>
##
## <Description>
## </Description>
## </ManSection>
##
BIND_GLOBAL( "TYPE_CHAR", NewType( CharsFamily, IsChar and IsInternalRep ) );
#############################################################################
##
## Types and family for strings
##
BIND_GLOBAL( "StringFamily", NewFamily( "StringsFamily", IsCharCollection ) );
BIND_GLOBAL( "TYPE_STRING_MUTABLE",
NewType( StringFamily, IsString and IsStringRep and
IsMutable ) );
BIND_GLOBAL( "TYPE_STRING_IMMUTABLE",
NewType( StringFamily, IsString and IsStringRep ) );
BIND_GLOBAL( "TYPE_STRING_NSORT_MUTABLE",
NewType (StringFamily, IsString and IsStringRep and
HasIsSSortedList and IsMutable ) );
BIND_GLOBAL( "TYPE_STRING_NSORT_IMMUTABLE",
NewType (StringFamily, IsString and IsStringRep and
HasIsSSortedList ) );
BIND_GLOBAL( "TYPE_STRING_SSORT_MUTABLE",
NewType (StringFamily, IsString and IsStringRep and
IsSSortedList and IsMutable ) );
BIND_GLOBAL( "TYPE_STRING_SSORT_IMMUTABLE",
NewType (StringFamily, IsString and IsStringRep and
IsSSortedList ) );
#############################################################################
##
#F IsEmptyString( <str> ) . . . . . . . . . . . . . . . empty string tester
##
## <#GAPDoc Label="IsEmptyString">
## <ManSection>
## <Func Name="IsEmptyString" Arg='str'/>
##
## <Description>
## <Ref Func="IsEmptyString"/> returns <K>true</K> if <A>str</A> is the
## empty string in the representation <Ref Filt="IsStringRep"/>,
## and <K>false</K> otherwise.
## Note that the empty list <C>[]</C> and the empty string <C>""</C> have
## the same type, the recommended way to distinguish them is via
## <Ref Func="IsEmptyString"/>.
## For formatted printing, this distinction is sometimes necessary.
## <!-- The type is the same because <C>IsStringRep</C> is not <E>set</E> in this type,-->
## <!-- and <C>IsPlistRep</C> is <E>set</E>,-->
## <!-- although <E>calling</E> <C>IsStringRep</C> for <C>[]</C> yields <K>false</K>,-->
## <!-- and <E>calling</E> <C>IsPlistRep</C> for <C>""</C> yields <K>false</K>, too.-->
## <P/>
## <Example><![CDATA[
## gap> l:= [];; IsString( l ); IsEmptyString( l ); IsEmpty( l );
## true
## false
## true
## gap> l; ConvertToStringRep( l ); l;
## [ ]
## ""
## gap> IsEmptyString( l ); IsEmptyString( "" ); IsEmptyString( "abc" );
## true
## true
## false
## gap> ll:= [ 'a', 'b' ]; IsStringRep( ll ); ConvertToStringRep( ll );
## "ab"
## false
## gap> ll; IsStringRep( ll );
## "ab"
## true
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
BIND_GLOBAL( "IsEmptyString",
obj -> IsString( obj )
and IsEmpty( obj )
and IsStringRep( obj ) );
############################################################################
##
#M String( <str> ) . . . . . . . . . . . . . . . . . . . . . . for a string
##
InstallMethod( String,
"for a string (do nothing)",
[ IsString ],
function(s)
if Length(s) = 0 and not IsStringRep(s) then
return "[ ]";
else
return s;
fi;
end);
############################################################################
##
#M String( <str> ) . . . . . . . . . . . . . . . . . . . . for a character
##
InstallMethod( String,
"for a character",
[ IsChar ],
function(ch)
local res; res := "\'"; Add(res, ch); Add(res, '\''); return res;
end);
#############################################################################
##
#F UserHomeExpand( <str> ) . . . . . . . . . . . . expand leading ~ in str
##
## <#GAPDoc Label="UserHomeExpand">
## <ManSection>
## <Func Name="UserHomeExpand" Arg='str'/>
## <Description>
## If the string <A>str</A> starts with a <C>'~'</C> character this
## function returns a new string with the leading <C>'~'</C> substituted by
## the user's home directory as stored in <C>GAPInfo.UserHome</C>.
## Otherwise <A>str</A> is returned unchanged.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
BIND_GLOBAL("UserHomeExpand", function(str)
if IsString(str) and Length(str) > 0 and str[1] = '~'
and IsString(GAPInfo.UserHome) and Length( GAPInfo.UserHome ) > 0 then
return Concatenation( GAPInfo.UserHome, str{[2..Length(str)]});
else
return str;
fi;
end);
# the character set definitions might be needed when processing files, thus
# they must come earlier.
BIND_GLOBAL("CHARS_DIGITS",MakeImmutable(LIST_SORTED_LIST("0123456789")));
BIND_GLOBAL("CHARS_UALPHA",
MakeImmutable(LIST_SORTED_LIST("ABCDEFGHIJKLMNOPQRSTUVWXYZ")));
BIND_GLOBAL("CHARS_LALPHA",
MakeImmutable(LIST_SORTED_LIST("abcdefghijklmnopqrstuvwxyz")));
BIND_GLOBAL("CHARS_ALPHA",
MakeImmutable(LIST_SORTED_LIST("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")));
BIND_GLOBAL("CHARS_SYMBOLS",
MakeImmutable(LIST_SORTED_LIST(" !\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~")));
#############################################################################
##
#F _StripEscapeSequences( <str> ) . . . . . remove escape sequences from str
##
## <#GAPDoc Label="_StripEscapeSequences">
## <ManSection >
## <Func Arg="str" Name="_StripEscapeSequences" />
## <Returns>string without escape sequences</Returns>
## <Description>
## This function returns the string one gets from the string <A>str</A> by
## removing all escape sequences. If <A>str</A> does not contain such a
## sequence then <A>str</A> itself is returned.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
BIND_GLOBAL("_StripEscapeSequences", function(str)
local esc, res, i, ls, p;
esc := CHAR_INT(27);
res := "";
i := 1;
ls := Length(str);
while i <= ls do
if str[i] = esc then
i := i+1;
while not str[i] in CHARS_ALPHA do
i := i+1;
od;
# first letter is last character of escape sequence
i := i+1;
# remove \027 marker of inner escape sequences as well
if IsBound(str[i]) and str[i] = '\027' then
i := i+1;
fi;
else
p := Position(str, esc, i);
if p=fail then
if i=1 then
# don't copy if no escape there
return str;
else
Append(res, str{[i..ls]});
return res;
fi;
else
Append(res, str{[i..p-1]});
i := p;
fi;
fi;
od;
return res;
end);
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