Re: Compiler 101

On Sun, 22 Jan 2005, Jon Masterson wrote:


> I am looking for pointers to starter information on building what is
> really an interpeter.
>
> I am working on a two stage interpeter -
> similar to Java - first stage which is with the code editor does
> syntax checking and analyes the code turning it into a series of
> tokens and associated data. The second stage runs on the users
> computer and executes the tokens.


I would call these two stages "scanning" and "parsing",
whereby I would describe them somewhat differently than
you have done.


> [...] and would appreciate and pointers to where I can read up
> on basic compiler/interpreter principles.


I recommend the GNU Bison manual. The moderator of this
newsgroup, John R. Levine, is also the author of the book
_Lex and Yacc_.


> At the moment, for example, I cannot allow nesting as I have no clue
> as to how to handle that now.


Nesting is easy. You just have to define a data structure
to represent your source of input. Let's call it
`Input_Struct'. An `Input_Struct' should have a data member
that references a source of input, i.e., a file descriptor,
a `FILE', an `istream', a `string', or whatever. You might
want to make this data member a pointer.
`Input_Struct' should also contain a data member of type
`Input_Struct*', which you might want to call `up'.
This is the basis for a linked list of `Input_Structs'.
When you need nesting, you allocate memory for a new
`Input_Struct' dynamically and push it onto the linked list.
When you're done reading from the input source it
represents, you pop it off.


If you want to see how I do this, my code is available at:
http://savannah.gnu.org/cgi-bin/viewcvs/3dldf/3dldf/Group/CWEB/


I do actually use the names `Input_Struct' and `up'.


If you do decide to use GNU Bison, you might want to look at
the archives of the `help-bison@gnu.org' mailing list:
http://lists.gnu.org/archive/html/help-bison/


Laurence Finston
http://www.gnu.org/software/3dldf/LDF.html

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