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#############################################################################
##
#W json.g GAP 4 package AtlasRep Thomas Breuer
##
## This file defines and implements a conversion between certain low level
## GAP objects and JSON (JavaScript Object Notation).
##
#############################################################################
##
## <#GAPDoc Label="JsonIntro">
## We define a mapping between certain &GAP; objects and
## JSON (JavaScript Object Notation) texts (see <Cite Key="JSON"/>),
## as follows.
## <P/>
## <List>
## <Item>
## The three &GAP; values <K>true</K>, <K>false</K>, and <K>fail</K>
## correspond to the JSON texts <C>true</C>, <C>false</C>,
## and <C>null</C>, respectively.
## </Item>
## <Item>
## &GAP; strings correspond to JSON strings;
## special characters in a &GAP; string (control characters ASCII <M>0</M>
## to <M>31</M>, backslash and double quote) are mapped as defined in
## JSON's specification, and other ASCII characters are kept as they are;
## if a &GAP; string contains non-ASCII characters, it is assumed that
## it is UTF-8 encoded, and one may choose either to keep non-ASCII
## characters as they are, or to create an ASCII only JSON string, using
## JSON's syntax for Unicode code points (<Q><C>\uXXXX</C></Q>);
## in the other direction, JSON strings are assumed to be UTF-8 encoded,
## and are mapped to UTF-8 encoded &GAP; strings, by keeping the non-ASCII
## characters and converting substrings of the form <C>\uXXXX</C>
## accordingly.
## </Item>
## <Item>
## &GAP; integers (in the sense of <Ref Func="IsInt" BookName="ref"/>)
## are mapped to JSON numbers that consist of digits and optionally
## a leading sign character <C>-</C>;
## in the other direction, JSON numbers of this form and also JSON numbers
## that involve no decimal dots and have no negative exponent
## (for example <C>"2e3"</C>) are mapped to &GAP; integers.
## </Item>
## <Item>
## &GAP; rationals (in the sense of <Ref Func="IsRat" BookName="ref"/>)
## which are not integers are represented by
## JSON floating point numbers;
## the JSON representation (and hence the precision) is given by
## first applying <Ref Attr="Float" BookName="ref"/> and then
## <Ref Attr="String" BookName="ref"/>.
## </Item>
## <Item>
## &GAP; floats (in the sense of Chapter
## <Ref Chap="Floats" BookName="ref"/> in the &GAP; Reference Manual)
## are mapped to JSON floating point numbers;
## the JSON representation (and hence the precision) is given by
## applying <Ref Attr="String" BookName="ref"/>;
## in the other direction, JSON numbers that involve a decimal dot or
## a negative exponent are mapped to &GAP; floats.
## </Item>
## <Item>
## (Nested and not self-referential) dense &GAP; lists of objects
## correspond to JSON arrays such that the list entries correspond
## to each other.
## (Note that JSON does not support non-dense arrays.)
## </Item>
## <Item>
## (Nested and not self-referential) &GAP; records correspond to JSON
## objects such that both labels (which are strings in &GAP; and JSON)
## and values correspond to each other.
## </Item>
## </List>
## <P/>
## The &GAP; functions <Ref Func="AGR.JsonText"/> and
## <Ref Func="AGR.GapObjectOfJsonText"/> can be used to create a JSON
## text from a suitable &GAP; object and the &GAP; object that
## corresponds to a given JSON text, respectively.
## <P/>
## Note that the composition of the two functions is in general <E>not</E>
## the identity mapping,
## because <Ref Func="AGR.JsonText"/> accepts non-integer rationals,
## whereas <Ref Func="AGR.GapObjectOfJsonText"/> does not create such
## objects.
## <P/>
## Note also that the results of <Ref Func="AGR.JsonText"/> do not contain
## information about dependencies between common subobjects.
## This is another reason why applying first <Ref Func="AGR.JsonText"/> and
## then <Ref Func="AGR.GapObjectOfJsonText"/> may yield a &GAP; object with
## different behaviour.
## <P/>
## Applying <Ref Func="AGR.JsonText"/> to a self-referential object
## such as <C>[ ~ ]</C> will raise a <Q>recursion depth trap</Q> error.
##
## <Subsection Label="subsect:WhyJSON">
## <Heading>Why JSON?</Heading>
##
## The aim of this JSON interface is to read and write certain data files
## with &GAP; such that these files become easily accessible independent
## of &GAP;.
## The function <Ref Func="AGR.JsonText"/> is intended just as a prototype,
## variants of this function are very likely to appear in other contexts,
## for example in order to force certain line formatting or ordering of
## record components.
## <P/>
## It is <E>not</E> the aim of the JSON interface to provide self-contained
## descriptions of arbitrary &GAP; objects, in order to read them into a
## &GAP; session.
## Note that those &GAP; objects for which a JSON equivalent exists (and
## many more) can be easily written to files as they are,
## and &GAP; can read them efficiently.
## On the other hand, more complicated &GAP; objects can be written and read
## via the so-called <E>pickling</E>, for which a framework is provided by
## the &GAP; package <Package>IO</Package> <Cite Key="IO"/>.
## <P/>
## Here are a few situations which are handled well by pickling but which
## cannot be addressed with a JSON interface.
## <P/>
## <List>
## <Item>
## Pickling and unpickling take care of common subobjects of the given
## &GAP; object.
## The following example shows that the applying first
## <Ref Func="AGR.JsonText"/> and then
## <Ref Func="AGR.GapObjectOfJsonText"/>
## may yield an object which behaves differently.
## <P/>
## <Example><![CDATA[
## gap> l:= [ [ 1 ] ];; l[2]:= l[1];; l;
## [ [ 1 ], [ 1 ] ]
## gap> new:= AGR.GapObjectOfJsonText( AGR.JsonText( l ) ).value;
## [ [ 1 ], [ 1 ] ]
## gap> Add( l[1], 2 ); l;
## [ [ 1, 2 ], [ 1, 2 ] ]
## gap> Add( new[1], 2 ); new;
## [ [ 1, 2 ], [ 1 ] ]
## ]]></Example>
## </Item>
## <Item>
## &GAP; admits self-referential objects, for example as follows.
## <P/>
## <Example><![CDATA[
## gap> l:= [];; l[1]:= l;;
## ]]></Example>
## <P/>
## Pickling and unpickling take care of self-referential objects,
## but <Ref Func="AGR.JsonText"/> does not support the conversion of such
## objects.
## </Item>
## </List>
## </Subsection>
## <#/GAPDoc>
##
#############################################################################
##
## Every GAP function that produces a string for the outside world
## must say something about the encoding of this string.
## We provide a function that produces an ASCII string
## and a function that assumes UTF-8 encoding of GAP strings,
## and keeps this encoding except if the JSON specification prescribes
## something different.
##
#############################################################################
##
#F AGR.JsonStringEncodeKeep( <string> )
##
## creates a string that describes the GAP string <string>
## as a JSON string that has the same encoding as <string>.
## We replace backslashes by double backslashes,
## escape double quotes,
## and replace the control characters 0, 1, ..., 31
## by the corresponding values in JSON's '\uXXXX' format.
##
## Note that we do not check whether <string> is a valid
## UTF-8 encoded string.
##
AGR.JsonStringEncodeKeep:= function( string )
local replace, pair;
replace:= [
[ "\\", "\\\\" ], [ "\"", "\\\"" ],
[ "\000", "\\u0000" ], [ "\>", "\\u0001" ], [ "\<", "\\u0002" ],
[ "\c", "\\u0003" ], [ "\004", "\\u0004" ], [ "\005", "\\u0005" ],
[ "\006", "\\u0006" ], [ "\007", "\\u0007" ], [ "\b", "\\b" ],
[ "\t", "\\t" ], [ "\n", "\\n" ], [ "\013", "\\u000B" ],
[ "\014", "\\f" ], [ "\r", "\\r" ], [ "\016", "\\u000E" ],
[ "\017", "\\u000F" ], [ "\020", "\\u0010" ], [ "\021", "\\u0011" ],
[ "\022", "\\u0012" ], [ "\023", "\\u0013" ], [ "\024", "\\u0014" ],
[ "\025", "\\u0015" ], [ "\026", "\\u0016" ], [ "\027", "\\u0017" ],
[ "\030", "\\u0018" ], [ "\031", "\\u0019" ], [ "\032", "\\u001A" ],
[ "\033", "\\u001B" ], [ "\034", "\\u001C" ], [ "\035", "\\u001D" ],
[ "\036", "\\u001E" ], [ "\037", "\\u001F" ],
];
for pair in replace do
string:= ReplacedString( string, pair[1], pair[2] );
od;
return string;
end;
#############################################################################
##
#F AGR.JsonStringEncodeASCII( <string> )
##
## creates an ASCII string that describes the GAP string <string>
## as a JSON string.
## We replace backslashes by double backslashes,
## escape double quotes,
## and replace the control characters 0, 1, ..., 31
## by the corresponding values in JSON's '\uXXXX' format.
## Moreover, we rewrite all Unicode code points
## except lower half ASCII to JSON's '\uXXXX' format.
## Note that code points above U+FFFF are encoded via
## UTF-16 surrogate pairs, using the reserved codepoints U+D800 to U+DBFF
## for the first part and U+DC00 to U+DFFF for the second part.
##
## If <string> is not a valid UTF-8 encoded string then 'fail' is returned.
##
AGR.JsonStringEncodeASCII:= function( string )
local encodesmall, ustr, res, n, n2;
encodesmall:= [ "\\u0000", "\\u0001", "\\u0002", "\\u0003", "\\u0004",
"\\u0005", "\\u0006", "\\u0007", "\\b", "\\t", "\\n", "\\u000B", "\\f",
"\\r", "\\u000E", "\\u000F", "\\u0010", "\\u0011", "\\u0012", "\\u0013",
"\\u0014", "\\u0015", "\\u0016", "\\u0017", "\\u0018", "\\u0019",
"\\u001A", "\\u001B", "\\u001C", "\\u001D", "\\u001E", "\\u001F", " ",
"!", "\\\"" ];
ustr:= Unicode( string );
if ustr = fail then
return fail;
fi;
res:= "";
for n in IntListUnicodeString( ustr ) do
if n < 35 then
Append( res, encodesmall[ n+1 ] );
elif n = 92 then
Append( res, "\\\\" );
elif n < 128 then
Add( res, CHAR_INT( n ) );
elif n < 256 then
Append( res, "\\u00" );
Append( res, HexStringInt( n ) );
elif n < 4096 then
Append( res, "\\u0" );
Append( res, HexStringInt( n ) );
elif n < 65536 then
Append( res, "\\u" );
Append( res, HexStringInt( n ) );
elif n < 1114112 then
n:= n - 65536;
n2:= n mod 1024;
Append( res, "\\u" );
Append( res, HexStringInt( ( n - n2 ) / 1024 + 55296 ) );
Append( res, "\\u" );
Append( res, HexStringInt( n2 + 56320 ) );
else
return fail;
fi;
od;
return res;
end;
#############################################################################
##
#F AGR.JsonText( <obj>[, <mode>] )
##
## <#GAPDoc Label="AGR.JsonText">
## <ManSection>
## <Func Name="AGR.JsonText" Arg='obj[, mode]'/>
##
## <Returns>
## a new mutable string that describes <A>obj</A> as a JSON text,
## or <K>fail</K>.
## </Returns>
##
## <Description>
## If <A>obj</A> is a &GAP; object for which a corresponding JSON text
## exists, according to the mapping described above,
## then such a JSON text is returned.
## Otherwise, <K>fail</K> is returned.
## <P/>
## If the optional argument <A>mode</A> is given and has the value
## <C>"ASCII"</C> then the result in an ASCII string,
## otherwise the encoding of strings that are involved in <A>obj</A>
## is kept.
## <P/>
## <Example><![CDATA[
## gap> AGR.JsonText( [] );
## "[]"
## gap> AGR.JsonText( "" );
## "\"\""
## gap> AGR.JsonText( "abc\ndef\cghi" );
## "\"abc\\ndef\\u0003ghi\""
## gap> AGR.JsonText( rec() );
## "{}"
## gap> AGR.JsonText( [ , 2 ] );
## fail
## gap> str:= [ '\303', '\266' ];; # umlaut o
## gap> json:= AGR.JsonText( str );; List( json, IntChar );
## [ 34, 195, 182, 34 ]
## gap> AGR.JsonText( str, "ASCII" );
## "\"\\u00F6\""
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
AGR.JsonText:= function( arg )
local mode, stringencode, obj, res, subobj, next, names, nam;
stringencode:= AGR.JsonStringEncodeKeep;
if Length( arg ) = 1 then
obj:= arg[1];
mode:= "";
elif Length( arg ) = 2 and IsBound( GAPInfo ) then
obj:= arg[1];
mode:= arg[2];
if mode = "ASCII" then
stringencode:= AGR.JsonStringEncodeASCII;
fi;
else
Error( "usage: AGR.JsonText( <obj>[, \"ASCII\"] )" );
fi;
if IsString( obj ) and ( IsStringRep( obj ) or not IsEmpty( obj ) ) then
obj:= stringencode( obj );
if obj = fail then
return fail;
else
return Concatenation( "\"", obj, "\"" );
fi;
elif IsInt( obj ) then
return String( obj );
elif IsRat( obj ) then
return String( Float( obj ) );
elif IsFloat( obj ) then
return String( obj );
elif obj = true then
return "true";
elif obj = false then
return "false";
elif obj = fail then
return "null";
elif IsDenseList( obj ) then
res:= "[";
if Length( obj ) = 0 then
Add( res, ']' );
else
for subobj in obj do
next:= AGR.JsonText( subobj, mode );
if next = fail then
return fail;
fi;
Append( res, next );
Add( res, ',' );
od;
res[ Length( res ) ]:= ']';
fi;
elif IsRecord( obj ) then
res:= "{";
names:= RecNames( obj );
if Length( names ) = 0 then
Add( res, '}' );
else
for nam in names do
next:= AGR.JsonText( nam, mode );
if next = fail then
return fail;
fi;
Append( res, next );
Append( res, ":" );
next:= AGR.JsonText( obj.( nam ), mode );
if next = fail then
return fail;
fi;
Append( res, next );
Add( res, ',' );
od;
res[ Length( res ) ]:= '}';
fi;
else
return fail;
fi;
return res;
end;
#############################################################################
##
#F AGR.GapObjectOfJsonText( <string> )
##
## <#GAPDoc Label="AGR.GapObjectOfJsonText">
## <ManSection>
## <Func Name="AGR.GapObjectOfJsonText" Arg='string'/>
##
## <Returns>
## a new mutable record whose <C>value</C> component, if bound,
## contains a mutable &GAP; object that represents the JSON text
## <A>string</A>.
## </Returns>
## <Description>
## If <A>string</A> is a string that represents a JSON text
## then the result is a record with the components <C>value</C>
## (the corresponding &GAP; object in the sense of the above interface) and
## <C>status</C> (value <K>true</K>).
## Otherwise, the result is a record with the components
## <C>status</C> (value <K>false</K>) and <C>errpos</C> (the position in
## <A>string</A> where the string turns out to be not valid JSON).
## <P/>
## <Example><![CDATA[
## gap> AGR.GapObjectOfJsonText( "{ \"a\": 1 }" );
## rec( status := true, value := rec( a := 1 ) )
## gap> AGR.GapObjectOfJsonText( "{ \"a\": x }" );
## rec( errpos := 8, status := false )
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
## rules for UTF-8 encoding of unicode code points:
## 0000, ..., 007F in 1 byte, as 0xxxxxxx (7 bits)
## 0080, ..., 07FF in 2 bytes, as 110xxxxx 10xxxxxx (5+6 bits)
## 0800, ..., FFFF in 3 bytes, as 1110xxxx 10xxxxxx 10xxxxxx (4+6+6 bits)
## 10000, ..., 10FFFF in 4 bytes, as 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
## (3+6+6+6 bits)
##
## For example, U+0070 is encoded by 70, and U+0080 by C2 80.
## Not all such sequences of bytes represent code points,
## for example 0800 is binary 00001000 00000000,
## which is encoded as 11100000 10100000 10000000.
##
AGR.GapObjectOfJsonText:= function( string )
local len, whitespace, res, pos, expectstringor\}, expectstring,
SIGNEDCHARSDIGITS, HEXCHARS, c, val, i, pos2, hex, high, low,
number, dpos, pos3, pos4, pos5, expsign, exp, new, pair;
if not IsString( string ) then
Error( "<string> must be a nonempty string" );
fi;
len:= Length( string );
if len = 0 then
Error( "<string> must be a nonempty string" );
fi;
# Whitespace is defined as sequence of the HEX characters 09, 0A, 0D, 20.
whitespace:= "\t\n\r ";
res:= rec( type:= "unknown" );
pos:= 1;
expectstringor\}:= false;
expectstring:= false;
SIGNEDCHARSDIGITS:= "-0123456789";
IsSSortedList( SIGNEDCHARSDIGITS ); # store that this is strictly sorted
HEXCHARS:= "0123456789ABCDEFabcdef";
IsSSortedList( HEXCHARS ); # store that this is strictly sorted
while pos <= len do
c:= string[ pos ];
if c in whitespace then
# Ignore whitespace.
pos:= pos + 1;
elif c = '\"' then
# A string follows.
# Rewrite the substrings \b, \f, \n, \r, \t, \\, \/,
# and interpret \uXXXX.
val:= "";
i:= pos + 1;
while i <= len do
c:= string[i];
if c = '\"' then
# The string is complete.
pos2:= i;
break;
elif c = '\\' then
# Deal with a special character.
if i = len then
return rec( status:= false, errpos:= pos );
fi;
i:= i+1;
c:= string[i];
if c in "\\\"/" then
Add( val, c );
elif c = 't' then
Add( val, '\t' );
elif c = 'r' then
Add( val, '\r' );
elif c = 'n' then
Add( val, '\n' );
elif c = 'b' then
Add( val, '\b' );
elif c = 'f' then
Add( val, '\014' );
elif c = 'u' then
# Add the encoding of a unicode code point.
if len < i + 4 then
return rec( status:= false, errpos:= pos );
fi;
hex:= string{ [ i+1 .. i+4 ] };
if not IsSubset( HEXCHARS, hex ) then
return rec( status:= false, errpos:= pos );
elif hex[1] in "Dd" then
if hex[2] in "CDEFcdef" then
# \uDC00 to \uDFFF must occur only as the second half
# of a UTF-16 surrogate pair.
return rec( status:= false, errpos:= pos );
elif hex[2] in "89ABab" then
# This is the first half of a UTF-16 surrogate pair.
high:= IntHexString( hex ) - 55296;
if len < i + 10 or string{ [ i+5, i+6 ] } <> "\\u" then
return rec( status:= false, errpos:= pos );
fi;
hex:= string{ [ i+7 .. i+10 ] };
if not ( IsSubset( HEXCHARS, hex )
and hex[1] in "Dd" and hex[2] in "CDEFcdef" ) then
return rec( status:= false, errpos:= pos );
fi;
low:= IntHexString( hex ) - 56320;
# Use an undocumented GAPDoc function.
Append( val, UNICODE_RECODE.UTF8UnicodeChar(
1024 * high + low + 65536 ) );
i:= i + 10;
else
# Use an undocumented GAPDoc function.
Append( val, UNICODE_RECODE.UTF8UnicodeChar(
IntHexString( hex ) ) );
i:= i + 4;
fi;
else
# Use an undocumented GAPDoc function.
Append( val, UNICODE_RECODE.UTF8UnicodeChar(
IntHexString( hex ) ) );
i:= i + 4;
fi;
else
return rec( status:= false, errpos:= pos );
fi;
elif IntChar( c ) <= 31 then
return rec( status:= false, errpos:= pos );
else
Add( val, c );
fi;
i:= i + 1;
od;
if len < i then
return rec( status:= false, errpos:= pos );
fi;
res.type:= "string";
res.value:= val;
expectstringor\}:= false;
expectstring:= false;
pos:= pos2 + 1;
elif expectstring or ( expectstringor\} and c <> '}' ) then
# We had just opened an object, or had just read a ',' in an object.
return rec( status:= false, errpos:= pos );
elif c in SIGNEDCHARSDIGITS then
# A number follows.
res.type:= "number";
pos2:= pos + 1;
if c = '-' then
number:= 0;
else
number:= POS_LIST_DEFAULT( CHARS_DIGITS, c, 0 ) - 1;
fi;
while pos2 <= len do
dpos:= POS_LIST_DEFAULT( CHARS_DIGITS, string[ pos2 ], 0 );
if dpos = fail then
break;
fi;
number:= 10 * number + dpos - 1;
pos2:= pos2 + 1;
od;
if ( c = '-' and ( pos2 = pos + 1 or ( pos + 2 < pos2 and
string[ pos + 1 ] = '0' ) ) ) or
( c = '0' and pos + 1 < pos2 ) then
return rec( status:= false, errpos:= pos );
elif len < pos2 then
# end of the string
if c = '-' then
number:= - number;
fi;
res.value:= number;
pos:= pos2;
elif string[ pos2 ] = '.' then
# A fractional part follows, we will create a float.
pos3:= pos2 + 1;
while pos3 <= len and string[ pos3 ] in CHARS_DIGITS do
pos3:= pos3 + 1;
od;
if pos3 = pos2 + 1 then
return rec( status:= false, errpos:= pos2 );
elif len < pos3 then
res.value:= Float( string{ [ pos .. pos3 - 1 ] } );
pos:= pos3;
elif string[ pos3 ] in "eE" then
# An exponent follows after the fractional part:
# [ pos .. pos2 - 1 ] is the integer part,
# [ pos2 + 1 .. pos3 - 1 ] is the fractional part,
# [ pos4 .. pos5 - 1 ] is the exponent, including the sign.
pos4:= pos3;
if len = pos4 then
return rec( status:= false, errpos:= pos3 );
elif string[ pos4 + 1 ] = '+' then
pos4:= pos4 + 1;
elif string[ pos4 + 1 ] = '-' then
pos4:= pos4 + 1;
fi;
pos5:= pos4 + 1;
while pos5 <= len and string[ pos5 ] in CHARS_DIGITS do
pos5:= pos5 + 1;
od;
if pos4 + 1 = pos5 then
return rec( status:= false, errpos:= pos3 );
fi;
res.value:= Float( string{ [ pos .. pos5 - 1 ] } );
pos:= pos5;
else
# There is no exponent.
res.value:= Float( string{ [ pos .. pos3 - 1 ] } );
pos:= pos3;
fi;
elif string[ pos2 ] in "eE" then
# An integer followed by an exponent (perhaps create an integer).
# [ pos .. pos2-1 ] is the integer part,
# [ pos3+1 .. pos4 - 1 ] is the abs. value of the exponent,
# expsign det. the sign
pos3:= pos2;
expsign:= false;
if len = pos3 then
return rec( status:= false, errpos:= pos2 );
elif string[ pos3 + 1 ] = '+' then
pos3:= pos3 + 1;
elif string[ pos3 + 1 ] = '-' then
pos3:= pos3 + 1;
expsign:= true;
fi;
pos4:= pos3 + 1;
while pos4 <= len and string[ pos4 ] in CHARS_DIGITS do
pos4:= pos4 + 1;
od;
if pos3 + 1 = pos4 then
return rec( status:= false, errpos:= pos3 );
elif expsign then
# We create a float.
res.value:= Float( string{ [ pos .. pos4 - 1 ] } );
else
# We create an integer.
exp:= 0;
for i in [ pos3 + 1 .. pos4 - 1 ] do
dpos:= POSITION_SORTED_LIST( CHARS_DIGITS, string[i] );
exp:= 10 * exp + dpos - 1;
od;
if c = '-' then
number:= - number;
fi;
res.value:= number * 10 ^ exp;
fi;
pos:= pos4;
else
# The number is an integer.
if c = '-' then
number:= - number;
fi;
res.value:= number;
pos:= pos2;
fi;
elif c = '[' then
# An array follows.
res.type:= "list";
new:= rec( type:= "unknown", parent:= res );
res.entries:= [ new ];
res.nrentries:= 1;
res:= new;
pos:= pos + 1;
elif c = '{' then
# An object follows.
res.type:= "record";
expectstringor\}:= true;
new:= rec( type:= "string", parent:= res );
res.pairs:= [ [ new ] ];
res.nrpairs:= 1;
res.lenlastpair:= 1;
res:= new;
pos:= pos + 1;
elif c = '}' then
# If we are processing an object then it is closed now.
if not IsBound( res.parent ) then
return rec( status:= false, errpos:= pos );
fi;
expectstringor\}:= false;
res:= res.parent;
if res.type <> "record" then
return rec( status:= false, errpos:= pos );
elif res.nrpairs = 1 and res.lenlastpair = 1
and not IsBound( res.pairs[1][1].value ) then
# The record is empty.
res.value:= rec();
elif res.lenlastpair = 1 then
return rec( status:= false, errpos:= pos );
else
res.value:= rec();
for pair in res.pairs do
res.value.( pair[1].value ):= pair[2].value;
od;
fi;
pos:= pos + 1;
elif c = ']' then
# If we are processing a list then it is closed now.
if not IsBound( res.parent ) then
return rec( status:= false, errpos:= pos );
fi;
res:= res.parent;
if res.type <> "list" then
return rec( status:= false, errpos:= pos );
elif res.nrentries = 1 and res.entries[1].type= "unknown" then
# The list is empty.
res.value:= [];
elif res.entries[ res.nrentries ].type= "unknown" then
return rec( status:= false, errpos:= pos );
else
res.value:= List( res.entries, x -> x.value );
fi;
pos:= pos + 1;
elif c = ',' then
# If we process an object or array then the next entry follows.
if not IsBound( res.parent ) or not IsBound( res.value ) then
return rec( status:= false, errpos:= pos );
fi;
res:= res.parent;
if res.type = "list" then
# We have processed a value.
res.nrentries:= res.nrentries + 1;
new:= rec( type:= "unknown", parent:= res );
res.entries[ res.nrentries ]:= new;
res:= new;
elif res.type = "record" and res.lenlastpair = 2 then
# We have processed both a label and a value.
expectstring:= true;
res.nrpairs:= res.nrpairs + 1;
new:= rec( type:= "string", parent:= res );
res.pairs[ res.nrpairs ]:= [ new ];
res.lenlastpair:= 1;
res:= new;
else
return rec( status:= false, errpos:= pos );
fi;
pos:= pos + 1;
elif c = ':' then
# In an object, this character separates labels and values.
if res.type <> "string" then
return rec( status:= false, errpos:= pos );
fi;
res:= res.parent;
if res.type <> "record" or res.lenlastpair <> 1 then
return rec( status:= false, errpos:= pos );
fi;
# We have just processed a label.
new:= rec( type:= "unknown", parent:= res );
res.pairs[ res.nrpairs ][2]:= new;
res.lenlastpair:= 2;
res:= new;
pos:= pos + 1;
elif c = 't' then
# true follows.
if len < pos + 3 or string{ [ pos .. pos + 3 ] } <> "true" then
return rec( status:= false, errpos:= pos );
fi;
res.type:= "constant";
res.value:= true;
pos:= pos + 4;
elif c = 'f' then
# false follows.
if len < pos + 4 or string{ [ pos .. pos + 4 ] } <> "false" then
return rec( status:= false, errpos:= pos );
fi;
res.type:= "constant";
res.value:= false;
pos:= pos + 5;
elif c = 'n' then
# null follows.
if len < pos + 3 or string{ [ pos .. pos + 3 ] } <> "null" then
return rec( status:= false, errpos:= pos );
fi;
res.type:= "constant";
res.value:= fail;
pos:= pos + 4;
else
return rec( status:= false, errpos:= pos );
fi;
od;
if not IsBound( res.value ) or IsBound( res.parent) then
return rec( status:= false, errpos:= pos );
fi;
return rec( value:= res.value, status:= true );
end;
#############################################################################
##
#E
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