after read mono

use the token () method from the cs-tokenizer.cs , i can recognize how the csharp compiler to work. follow this,that is the most important part of the driver : static void tokenize_file (SourceFile file) firstly ,the mcs used some expression to replace the general parser which is got from book.(like as " if ( is_identifier || is_identifier_numeric){...} "); Each time a token is returned, the location for the token is recorded into the `Location' property, that can be accessed by the parser. The parser retrieves the Location properties as it builds its internal representation to allow the semantic analysis phase to produce error messages that can pin point the location of the problem. Some tokens have values associated with it, for example when the tokenizer encounters a string, it will return a LITERAL_STRING token, and the actual string parsed will be available in the `Value' property of the tokenizer. The same mechanism is used to return integers and floating point numbers. //

//i can not understand that why design the location. //

** Locations Locations are encoded as a 32-bit number (the Location struct) that map each input source line to a linear number. As new files are parsed, the Location manager is informed of the new file, to allow it to map back from an int constant to a file + line number. Prior to parsing/tokenizing any source files, the compiler generates a list of all the source files and then reserves the low N bits of the location to hold the source file, where N is large enough to hold at least twice as many source files as were specified on the command line (to allow for a #line in each file). The upper 32-N bits are the line number in that file. The token 0 is reserved for ``anonymous'' locations, ie. if we don't know the location (Location.Null). The tokenizer also tracks the column number for a token, but this is currently not being used or encoded. It could probably be encoded in the low 9 bits, allowing for columns from 1 to 512 to be encoded.