  
  [1X83 [33X[0;0YLibrary Files[133X[101X
  
  [33X[0;0YThis  chapter  describes  some  of  the  conventions used in the [5XGAP[105X library
  files. These conventions are intended as a help on how to read library files
  and  how  to find information in them. So everybody is recommended to follow
  these  conventions,  although they do not prescribe a compulsory programming
  style –[5XGAP[105X itself will not bother with the formatting of files.[133X
  
  [33X[0;0YFilenames  have  traditionally [5XGAP[105X adhered to the 8+3 convention (to make it
  possible to use the same filenames even on a MS-DOS file system) and been in
  lower  case  (systems  that  do  not recognize lower case in file names will
  convert  them  automatically to upper case). It is no longer so important to
  adhere  to  these conventions, but at the very least filenames should adhere
  to a 16+5 convention, and be distinct even after identifying upper and lower
  case.  Directory  names  of  packages,  however,  [13Xmust[113X be in lower case (the
  [2XLoadPackage[102X ([14X76.2-1[114X) command assumes this).[133X
  
  
  [1X83.1 [33X[0;0YFile Types[133X[101X
  
  [33X[0;0YThe  [5XGAP[105X  library consists of the following types of files, distinguished by
  their suffixes:[133X
  
  [8X[10X.g[110X[8X [108X
        [33X[0;6YFiles  which  contain  parts of the [21Xinner workings[121X of [5XGAP[105X. These files
        usually   do   not  contain  mathematical  functionality,  except  for
        providing links to kernel functions.[133X
  
  [8X[10X.gd[110X[8X [108X
        [33X[0;6YDeclaration files. These files contain declarations of all categories,
        attributes, operations, and global functions. These files also contain
        the operation definitions in comments.[133X
  
  [8X[10X.gi[110X[8X [108X
        [33X[0;6YImplementation files. These files contain all installations of methods
        and global functions. Usually declarations of representations are also
        considered to be part of the implementation and are therefore found in
        the [10X.gi[110X files.[133X
  
  [33X[0;0YAs a rule of thumb, all [10X.gd[110X files are read in before the [10X.gi[110X files are read.
  Therefore  a  [10X.gi[110X  file usually may use any operation or global function (it
  has  been declared before), and no care has to be taken towards the order in
  which the [10X.gi[110X files are read.[133X
  
  
  [1X83.2 [33X[0;0YFinding Implementations in the Library[133X[101X
  
  [33X[0;0YFor  a  concretely  given  function,  you  can  use [2XFilenameFunc[102X ([14X5.1-4[114X) and
  [2XStartlineFunc[102X  ([14X5.1-5[114X)  for finding the file where this function is defined,
  and the line in this file where the definition of this function starts. This
  does  not work for arbitrary functions, see Section [2XFilenameFunc[102X ([14X5.1-4[114X) for
  the restrictions.[133X
  
  [33X[0;0YIf  you are interested in getting the function which implements a method for
  specific arguments, you can use [14X7.2-1[114X. If [2XFilenameFunc[102X ([14X5.1-4[114X) does not work
  for  this  method then setting the print level of [14X7.2-1[114X higher will give you
  the  installation string for this method, which can be used for searching in
  library files.[133X
  
  [33X[0;0YTo   find   the  occurrence  of  functions,  methods,  function  names,  and
  installation  strings  in the library, one can use the [10Xgrep[110X tool under UNIX.
  To find a function, search for the function name in the [10X.gd[110X files; as global
  variables  are  usually declared only once, only few files will show up. The
  function installation is likely to occur in the corresponding [10X.gi[110X file.[133X
  
  [33X[0;0YTo  find a method from the known operation name and the installation string,
  search  for the string [21X[10XMethod([110X[121X (this catches both [2XInstallMethod[102X ([14X78.3-1[114X) and
  [2XInstallOtherMethod[102X  ([14X78.3-2[114X))  and  the installation string or the operation
  name.[133X
  
  [33X[0;0YThe  following  tools  from the [5XGAP[105X package [5XBrowse[105X can be used for accessing
  the code of functions.[133X
  
  [30X    [33X[0;6Y[2XBrowseGapMethods[102X  ([14XBrowseGapMethods???[114X)  shows  an  overview  of [5XGAP[105X's
        operations  and  methods, and allows one to navigate through the files
        that contain the implementations of the methods, using a pager.[133X
  
  [30X    [33X[0;6Y[2XBrowseProfile[102X  ([14XBrowseProfile???[114X)  shows profiling results (similar to
        [2XDisplayProfile[102X  ([14X7.8-9[114X))  and allows one to navigate through the files
        that  contain  the implementations of the functions that were actually
        used, using a pager.[133X
  
  
  [1X83.3 [33X[0;0YUndocumented Variables[133X[101X
  
  [33X[0;0YFor  several  global  variables  in [5XGAP[105X, no information is available via the
  help  system (see Section [14X'Tutorial: Help'[114X, for a quick overview of the help
  system,  or  Chapter [14X2[114X, for details). There are various reasons for [21Xhiding[121X a
  variable  from  the  user;  namely, the variable may be regarded as of minor
  importance  (for  example,  it  may  be  a function called by documented [5XGAP[105X
  functions  that  first  compute  many  input parameters for the undocumented
  function),  or it belongs to a part of [5XGAP[105X that is still experimental in the
  sense  that  the meaning of the variable has not yet been fixed or even that
  it  is  not  clear  whether  the  variable  will  vanish in a more developed
  version.[133X
  
  [33X[0;0YAs a consequence, it is dangerous to use undocumented variables because they
  are not guaranteed to exist or to behave the same in future versions of [5XGAP[105X.[133X
  
  [33X[0;0YConversely,  for [13Xdocumented[113X variables, the definitions in the [5XGAP[105X manual can
  be relied on for future [5XGAP[105X versions (unless they turn out to be erroneous);
  if  the  [5XGAP[105X  developers  find  that  some  piece  of  minor, but documented
  functionality  is an insurmountable obstacle to important developments, they
  may  make  the smallest possible incompatible change to the functionality at
  the  time of a major release. However, in any such case it will be announced
  clearly in the [5XGAP[105X Forum what has been changed and why.[133X
  
  [33X[0;0YSo  on  the  one  hand,  the  developers  of [5XGAP[105X want to keep the freedom of
  changing  undocumented  [5XGAP[105X code. On the other hand, users may be interested
  in using undocumented variables.[133X
  
  [33X[0;0YIn  this case, whenever you write [5XGAP[105X code involving undocumented variables,
  and  want  to  make sure that this code will work in future versions of [5XGAP[105X,
  you  may  ask  at  [7Xmailto:support@gap-system.org[107X for documentation about the
  variables  in  question.  The  [5XGAP[105X  developers  then  decide  whether  these
  variables shall be documented or not, and if yes, what the definitions shall
  be.[133X
  
  [33X[0;0YIn  the  former case, the new documentation is added to the [5XGAP[105X manual, this
  means that from then on, this definition is protected against changes.[133X
  
  [33X[0;0YIn the latter case (which may occur for example if the variables in question
  are  still  experimental), you may add the current values of these variables
  to  your  private  code  if  you want to be sure that nothing will be broken
  later due to changes in [5XGAP[105X.[133X
  
