The Lisp Reader

The Lisp reader is a program that reads input in character form and converts it into Lisp's internal form, including:

  1. Looking up symbol names to find the pointers to the corresponding symbol data structures in memory. Lisp structures within the computer always use pointers rather than names. The only times Lisp uses the name of a symbol are:
    1. When reading in the symbol, the Lisp reader looks up the symbol's name in a symbol table to find the corresponding pointer.

    2. When printing a symbol, Lisp follows a pointer from the symbol data structure to the string that is the symbol's print name and prints it as the external representation of the symbol.

  2. Building list structure for parenthesized expressions.

  3. Ignoring comments.

  4. Changing ' expr into (quote expr ).

  5. Performing other transformations of input into internal forms, e.g. converting numbers from printed form to machine binary.

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