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### 1 The Example Package

This chapter describes the GAP package Example. As its name suggests it is an example of how to create a GAP package. It has little functionality except for being a package.

See Sections 2.1, 2.2 and 2.3 for how to install, compile and load the Example package, or Appendix A for guidelines on how to write a GAP package.

If you are viewing this with on-line help, type:

gap> ?Example package


to see the functions provided by the Example package.

#### 1.1 The Main Functions

The following functions are available:

##### 1.1-1 ListDirectory
 ‣ ListDirectory( [dir] ) ( function )

lists the files in directory dir (a string) or the current directory if called with no arguments.

##### 1.1-2 FindFile
 ‣ FindFile( directory_name, file_name ) ( function )

searches for the file file_name in the directory tree rooted at directory_name and returns the absolute path names of all occurrences of this file as a list of strings.

 ‣ LoadedPackages( ) ( function )

returns a list with the names of the packages that have been loaded so far. All this does is execute

gap> RecNames( GAPInfo.PackagesLoaded );


You might like to check out some of the other information in the GAPInfo record (see Reference: GAPInfo).

##### 1.1-4 Which
 ‣ Which( prg ) ( function )

returns the path of the program executed if Exec(prg); is called, e.g.

gap> Which("date");
"/bin/date"
gap> Exec("date");
Fri 28 Jan 2011 16:22:53 GMT


##### 1.1-5 WhereIsPkgProgram
 ‣ WhereIsPkgProgram( prg ) ( function )

returns a list of paths of programs with name prg in the current packages loaded. Try:

gap> WhereIsPkgProgram( "hello" );


##### 1.1-6 HelloWorld
 ‣ HelloWorld( ) ( function )

executes the C program hello provided by the Example package.

##### 1.1-7 FruitCake
 ‣ FruitCake ( global variable )

is a record with the bits and pieces needed to make a boiled fruit cake. Its fields satisfy the criteria for Recipe (1.1-8).

##### 1.1-8 Recipe
 ‣ Recipe( cake ) ( operation )

displays the recipe for cooking cake, where cake is a record satisfying certain criteria explained here: its recognised fields are name (a string giving the type of cake or cooked item), ovenTemp (a string), cookingTime (a string), ingredients (a list of strings each containing an _ which is used to line up the entries and is replaced by a blank), method (a list of steps, each of which is a string or list of strings), and notes (a list of strings). The global variable FruitCake (1.1-7) provides an example of such a string.

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