This module contains the functions that read a source file.
Script basic has several passes until it can start to execute the code. The very first pass is to read the source lines from the files. The routines in this module perform this task and build up a linked list that contains the ascii values of the lines.
The input functions are parametrized, and the caller should support. If you have different system dependent file reading functions, or if you have the input file in some format in memory or in any other data holding space you can support these routines with character fetch functions.