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Value (computer science)

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Value (computer science)

In computer science, a value is an expression which cannot be evaluated any further (a normal form).[1] The members of a type are the values of that type.[2] For example, the expression 1 + 2 is not a value as it can be reduced to the expression 3. This expression cannot be reduced any further (and is a member of the type Nat) and therefore is a value.

The "value of a variable" is given by the corresponding mapping in the environment. In languages with assignable variables it becomes necessary to distinguish between the r-value (or contents) and the l-value (or location) of a variable.[3]

In declarative (high-level) languages, values have to be referentially transparent. This means that the resulting value is independent of the location in which a (sub-)expression needed to compute the value is stored. Only the contents of the location (the bits, whether they are 1 or 0) and their interpretation are significant.

}#invoke:anchor|main}}Assignment: l-values and r-values

Some languages use the idea of l-values and r-values. L-values have storage addresses that are programmatically accessible to the running program (e.g., via some address-of operator like "&" in C/C++), meaning that they are variables or dereferenced references to a certain memory location. R-values can be l-values (see below) or non-l-values—a term only used to distinguish from l-values. Consider the C expression 4 + 9. When executed, the computer generates an integer value of 13, but because the program has not explicitly designated where in the computer this 13 is stored, the expression is an r-value. On the other hand, if a C program declares a variable x and assigns the value of 13 to x, then the expression x has a value of 13 and is an l-value.

In C, the term l-value originally meant something that could be assigned to (hence the name, indicating it is on the left side of the assignment operator), but since the reserved word const (constant) was added to the language, the term is now 'modifiable l-value'. In C++11 a special semantic-glyph && exists, to denote the use/access of the expression's address for the compiler only; i.e., the address cannot be retrieved using the address-of, &, operator during the run-time of the program (see the use of move semantics).

This type of reference can be applied to all r-values including non-l-values as well as l-values. Some processors provide one or more instructions which take an immediate value, sometimes referred to as "immediate" for short. An immediate value is stored as part of the instruction which employs it, usually to load into, add to, or subtract from, a register. The other parts of the instruction are the opcode, and destination. The latter may be implicit. (A non-immediate value may reside in a register, or be stored elsewhere in memory, requiring the instruction to contain a direct or indirect address [e.g., index register address] to the value.)

The l-value expression designates (refers to) an object. A non-modifiable l-value is addressable, but not assignable. A modifiable l-value allows the designated object to be changed as well as examined. An r-value is any expression, a non-l-value is any expression that is not an l-value. One example is an "immediate value" (look below) and consequently not addressable.

The notion of l-values and r-values was introduced by CPL. The notions in an expression of r-value, l-value, and r-value/l-value are analogous to the parameter modes of input parameter (has a value), output parameter (can be assigned), and input/output parameter (has a value and can be assigned), though the technical details differ between contexts and languages.

In assembly language

A value can be virtually any kind of data by a given data type, for instance a string, a digit, a single letter.

Processors often support more than one size of immediate data, e.g. 8 or 16 bit, employing a unique opcode and mnemonic for each instruction variant. If a programmer supplies a data value that will not fit, the assembler issues an "Out of range" error message. Most assemblers allow an immediate value to be expressed as ASCII, decimal, hexadecimal, octal, or binary data. Thus, the ASCII character 'A' is the same as 65 or 0x41. The byte order of strings may differ between processors, depending on the assembler and computer architecture.

Notes

References

  • require('Module:No globals')

local function getCatForId( id )

   local title = mw.title.getCurrentTitle()
   local namespace = title.namespace
   if namespace == 0 then

return ''

   elseif namespace == 2 and not title.isSubpage then

return ''

   else

return ''

   end

end

local function viafLink( id )

   if not string.match( id, '^%d+$' ) then
       return false
   end
   return '.. id .. ' ' .. id .. '' .. getCatForId( 'VIAF' )

end

local function kulturnavLink( id )

   return '.. id .. ' id' 

end

local function sikartLink( id )

   return '.. id .. '&lng=en ' .. id .. '' 

end

local function tlsLink( id ) local id2 = mw.ustring.gsub(id, '%s', function(s) return mw.uri.encode(s, 'WIKI') end)

   return '.. id2 .. ' ' .. id .. '' 

end


local function ciniiLink( id )

   return '.. id .. '?l=en ' .. id .. '' 

end

local function bneLink( id )

   return '.. id .. ' ' .. id .. '' 

end


local function uscongressLink( id )

   return '.. id .. ' ' .. id .. '' 

end

local function narapersonLink( id )

   return '.. id .. ' ' .. id .. '' 

end

local function naraorganizationLink( id )

   return '.. id .. ' ' .. id .. '' 

end

local function botanistLink( id ) local id2 = mw.ustring.gsub(id, '%s', function(s) return mw.uri.encode(s, 'PATH') end)

   return '.. id2 .. ' ' .. id .. '' 

end

local function mgpLink( id )

   -- TODO Implement some sanity checking regex
   return '.. id .. ' ' .. id .. '' 

end

local function rslLink( id )

   -- TODO Implement some sanity checking regex
   return '.. id .. '&CON_LNG=ENG ' .. id .. ''

end

local function leonoreLink( id ) -- Identifiants allant de LH/1/1 à LH/2794/54 (légionnaires) -- Identifiants allant de C/0/1 à C/0/84 (84 légionnaires célèbres) -- Identifiants allant de 19800035/1/1 à 19800035/385/51670 (légionnaires décédés entre 1954 et 1977, et quelques dossiers de légionnaires décédés avant 1954)

   if not string.match( id, '^LH/%d%d?%d?%d?/%d%d?%d?$' ) and
      not string.match( id, '^C/0/%d%d?$' ) and
           not string.match( id, '^19800035/%d%d?%d?%d?/%d%d?%d?%d?%d?$' ) then
       return false
   end
   return '.. id .. ' ' .. id .. '' 

end

local function sbnLink( id )

   if not string.match( id, '^IT\\ICCU\\%d%d%d%d%d%d%d%d%d%d$' ) and not string.match( id, '^IT\\ICCU\\%u%u[%d%u]%u\\%d%d%d%d%d%d$' ) then
       return false
   end
   return '.. id .. ' ' .. id .. '' .. getCatForId( 'SBN' )

end

local function nkcLink( id ) return '.. id .. '&CON_LNG=ENG ' .. id .. '' end

local function nclLink( id )

   if not string.match( id, '^%d+$' ) then
       return false
   end
   return '.. id .. '&CON_LNG=ENG ' .. id .. '' 

end

local function ndlLink( id ) return '.. id .. ' ' .. id .. '' end

local function sudocLink( id )

   if not string.match( id, '^%d%d%d%d%d%d%d%d[%dxX]$' ) then
       return false
   end
   return '.. id .. ' ' .. id .. '' 

end

local function hlsLink( id )

   if not string.match( id, '^%d+$' ) then
       return false
   end
   return '.. id .. '.php ' .. id .. ''

end

local function lirLink( id )

   if not string.match( id, '^%d+$' ) then
       return false
   end
   return '.. id .. '.450.0.html ' .. id .. ''

end

local function splitLccn( id )

   if id:match( '^%l%l?%l?%d%d%d%d%d%d%d%d%d?%d?$' ) then
       id = id:gsub( '^(%l+)(%d+)(%d%d%d%d%d%d)$', '%1/%2/%3' )
   end
   if id:match( '^%l%l?%l?/%d%d%d?%d?/%d+$' ) then
        return mw.text.split( id, '/' )
   end
   return false

end

local function append(str, c, length)

   while str:len() < length do
       str = c .. str
   end
   return str

end

local function lccnLink( id )

   local parts = splitLccn( id )
   if not parts then
       return false
   end
   local lccnType = parts[1] ~= 'sh' and 'names' or 'subjects'
   id = parts[1] .. parts[2] .. append( parts[3], '0', 6 )
   return '.. lccnType .. '/' .. id .. ' ' .. id .. '' .. getCatForId( 'LCCN' )

end

local function mbLink( id )

   -- TODO Implement some sanity checking regex
   return '.. id .. ' ' .. id .. '' .. getCatForId( 'MusicBrainz' )

end

--Returns the ISNI check digit isni must be a string where the 15 first elements are digits local function getIsniCheckDigit( isni )

   local total = 0
   for i = 1, 15 do
       local digit = isni:byte( i ) - 48 --Get integer value
       total = (total + digit) * 2
   end
   local remainder = total % 11
   local result = (12 - remainder) % 11
   if result == 10 then
       return "X"
   end
   return tostring( result )

end

--Validate ISNI (and ORCID) and retuns it as a 16 characters string or returns false if it's invalid --See http://support.orcid.org/knowledgebase/articles/116780-structure-of-the-orcid-identifier local function validateIsni( id )

   id = id:gsub( '[ %-]', ):upper()
   if not id:match( '^%d%d%d%d%d%d%d%d%d%d%d%d%d%d%d[%dX]$' ) then
       return false
   end
   if getIsniCheckDigit( id ) ~= string.char( id:byte( 16 ) ) then
       return false
   end
   return id

end

local function isniLink( id )

   id = validateIsni( id )
   if not id then
       return false
   end
   return '.. id .. ' ' .. id:sub( 1, 4 ) .. ' ' .. id:sub( 5, 8 ) .. ' '  .. id:sub( 9, 12 ) .. ' '  .. id:sub( 13, 16 ) .. '' .. getCatForId( 'ISNI' )

end

local function orcidLink( id )

   id = validateIsni( id )
   if not id then
       return false
   end
   id = id:sub( 1, 4 ) .. '-' .. id:sub( 5, 8 ) .. '-'  .. id:sub( 9, 12 ) .. '-'  .. id:sub( 13, 16 )
   return '.. id .. ' ' .. id .. '' .. getCatForId( 'ORCID' )

end

local function gndLink( id )

   return '.. id .. ' ' .. id .. '' .. getCatForId( 'GND' )

end

local function selibrLink( id ) if not string.match( id, '^%d+$' ) then

       return false
   end
   return '.. id .. ' ' .. id .. '' .. getCatForId( 'SELIBR' )

end

local function bnfLink( id )

   --Add cb prefix if it has been removed
   if not string.match( id, '^cb.+$' ) then
       id = 'cb' .. id
   end
   return '.. id .. ' ' .. id .. ' .. id .. ' (data)' .. getCatForId( 'BNF' )

end

local function bpnLink( id )

   if not string.match( id, '^%d+$' ) then
       return false
   end
   return '.. id .. ' ' .. id .. '' .. getCatForId( 'BPN' )

end

local function ridLink( id )

   return '.. id .. ' ' .. id .. '' .. getCatForId( 'RID' )

end

local function bibsysLink( id )

   return '.. id .. '&feltselect=bs.autid ' .. id .. '' .. getCatForId( 'BIBSYS' )

end

local function ulanLink( id )

   return '.. id .. ' ' .. id .. '' .. getCatForId( 'ULAN' )

end

local function nlaLink( id ) return '.. id .. ' ' .. id .. '' .. getCatForId( 'NLA' ) end

local function rkdartistsLink( id ) return '.. id .. ' ' .. id .. '' .. getCatForId( 'RKDartists' ) end

local function getIdsFromWikidata( item, property )

   local ids = {}
   if not item.claims[property] then
       return ids
   end
   for _, statement in pairs( item.claims[property] ) do
         if statement.mainsnak.datavalue then
          table.insert( ids, statement.mainsnak.datavalue.value )
         end
   end
   return ids

end

local function matchesWikidataRequirements( item, reqs )

   for _, group in pairs( reqs ) do
       local property = 'p' .. group[1]
       local qid = group[2]
       if item.claims[property] ~= nil then
           for _, statement in pairs ( item.claims[property] ) do
                if statement.mainsnak.datavalue ~= nil then
                        if statement.mainsnak.datavalue.value['numeric-id'] == qid then
                        return true
                end
            end
           end
       end
   end
   return false

end

local function createRow( id, label, rawValue, link, withUid )

   if link then
       if withUid then
           return '* ' .. label .. ' ' .. link .. '\n'
       else
           return '* ' .. label .. ' ' .. link .. '\n'
       end
   else

return '* \n'

   end

end

--In this order: name of the parameter, label, propertyId in Wikidata, formatting function local conf = {

   { 'VIAF', 'VIAF', 214, viafLink },
   { 'LCCN', 'LCCN', 244, lccnLink },
   { 'ISNI', 'ISNI', 213, isniLink },
   { 'ORCID', 'ORCID', 496, orcidLink },
   { 'GND', 'GND', 227, gndLink },
   { 'SELIBR', 'SELIBR', 906, selibrLink },
   { 'SUDOC', 'SUDOC', 269, sudocLink },    
   { 'BNF', 'BNF', 268, bnfLink },
   { 'BPN', 'BPN', 651, bpnLink },
   { 'RID', 'ResearcherID', 1053, ridLink },
   { 'BIBSYS', 'BIBSYS', 1015, bibsysLink },
   { 'ULAN', 'ULAN', 245, ulanLink },
   { 'HDS', 'HDS', 902, hlsLink },
   { 'LIR', 'LIR', 886, lirLink },
   { 'MBA', 'MusicBrainz', 434, mbLink },
   { 'MGP', 'MGP', 549, mgpLink },    
   { 'NLA', 'NLA', 409, nlaLink },
   { 'NDL', 'NDL', 349, ndlLink },
   { 'NCL', 'NCL', 1048, nclLink },
   { 'NKC', 'NKC', 691, nkcLink },
   { 'Léonore', 'Léonore', 640, leonoreLink }, 
   { 'SBN', 'ICCU', 396, sbnLink },     
   { 'RLS', 'RLS', 947, rslLink },
   { 'Botanist', '[[Author ci 

External links

  • Value Object
  • Transfer Object Pattern
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