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Turbo Pascal contains many functions that read or write files, handle error messages and take care for compiler operation.
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This procedure loads Turbo Pascal library (a collection of units). It adjust each unit so that it starts on a segment boundary. Actually, each compiled unit is a group of symbol tables.
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Turbo Pascal needs to access files that may be located in different directories - located where the compiler is run or specified either in the configuration file or at the command line.
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Turbo Pascal needs to create, read from and write to files. Few simple routins take care for this.
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For each source file Turbo Pascal keeps a record with essential data like file handle, file name, current line number, current position, conditional compilation IF level, etc.
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Source files are read into buffer from where source lines are extracted. NextLine procedure moves to the next source line. If a line was read it increments counters and returns True, otherwise if there are no more source lines NextLine returns False.
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CompileUnit calls this procedure to create unit file which is in fact a collection of symbol tables. All segment addresses are cleared and symbol table data is written to the file.
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This short procedure reads unit from file to symbol tables. If header is not valid it reports error.
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