Front-end

Input files (or source files) are read by files_map.ad[sb]. Only regular files can be read, because they are read entirely before being scanned. This simplifies the scanner, but this also allows to have a unique index for each character in any file. Therefore the source location is a simple 32-bit integer whose type is Location_Type. From the location, files_map can deduce the source file (type is Source_File_Entry) and then the offset in the source file. There is a line table for each source file in order to speed-up the conversion from file offset to line number and column number.

The scanner (file vhdl-scanner.ad[sb]) reads the source files and creates token from them. The tokens are defined in file vhdl-tokens.ads. Tokens are scanned one by one, so the scanner doesn’t keep in memory the previous token. Integer or floating point numbers are special tokens because beside the token itself there is also a variable for the value of the number.

For identifiers there is a table containing all identifiers. This is implemented by file name_table.ad[sb]. Each identifier is associated to a 32-bit number (they are internalized). So the number is used to reference an identifier. About one thousand identifiers are predefined (by std_names.ad[sb]). Most of them are reserved identifiers (or keywords). When the scanner find an identifier, it checks if it is a keyword. In that case it changes the token to the keyword token.

The procedure scan is called to get the next token. The location of the token and the location after the token are available to store it in the parser tree.

The main client of the scanner is the parser.