GAP (Example) - Chapter 1: The Example Package

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1 The Example Package
1.1 The Main Functions
1.1-1 ListDirectory
1.1-2 FindFile
1.1-3 LoadedPackages
1.1-4 Which
1.1-5 WhereIsPkgProgram
1.1-6 HelloWorld
1.1-7 FruitCake
1.1-8 Recipe

### 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.

##### 1.1-3 LoadedPackages

`‣ 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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