Class Function

Class Function serves to keep track of the source code for a given executable, and other information needed to recompile it, such as the compiler used to translate from source to executable form.

This information could be kept in the executable itself, of course, but keeping it in a separate object has a number of advantages:

• The function instance exists before the first compile and between compiles and remains the same object between compiles, hence provides a stable place to keep the source code: A new executable will be created by each compile. The function provides a stable place to hang help information, for example.
• Potentially thousands of executables may be created from a single set of source code, if it describes a thunk or promise being used as a data constructor. Factoring all the source information out into a single shared function object provides space efficiency and reduced redundancy.
• Much code is more frequently executed than edited or compiled: by factoring the information needed for recompilation into a separate object from that needed for execution, the former can stay on disk when the latter is swapped into ram.

Class Function adds the following properties to those of Class Plain:

$S.arity:	Number of arguments accepted and returned.
$S.executable:   Most recently compiled executable. There may be others.
$S.compiler:     Program translating source to executable.
$S.fileName:    Debug information: Name of source file.
$S.fnLine:      Debug information: Starting line number in source file.
$S.lineNumbers: Debug information: vector of line numbers, one per bytecode.
$S.source:       String source code.
$S.localVariableNames: Vector of string names for local variables.
$S.specializedParameters:  NIL or count of required args for generic.
$S.defaultMethods:  NIL or mosKey of methods with t as 1st arg specializer.

Note: For convenience, the $S properties are also available in the public (default) propdir.

The fnLine value, and the integers in the lineNumbers vector, are all zero-based: The first line in a file is line zero, the first line in a function is line zero. However, users expect line numbers to begin at one, and text editors conventionally number them this way, so you should add one to either when displaying it.

As of version -1.0.0, compiler and debug information is not used. See section explodeArity.

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