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A simple lexer.

The procedures in this module surprisingly often suffice to parse an input stream. They either skip, or build and return tokens, according to inclusion or delimiting semantics. The list of characters to expect, include, or to break at may vary from one invocation of a function to another. This allows the functions to easily parse even context-sensitive languages.

EOF is generally frowned on, and thrown up upon if encountered. Exceptions are mentioned specifically. The list of expected characters (characters to skip until, or break-characters) may include an EOF "character", which is to be coded as the symbol, *eof*.

The input stream to parse is specified as a port, which is usually the last (and optional) argument. It defaults to the current input port if omitted.

If the parser encounters an error, it will throw an exception to the key parser-error. The arguments will be of the form (port message specialising-msg*).

The first argument is a port, which typically points to the offending character or its neighborhood. You can then use port-column and port-line to query the current position. message is the description of the error. Other arguments supply more details about the problem.

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