SourceFiles.org - Use the Source, Luke

Back to files

                                   LITHP
         A small simple LISP interpreter

                  Scott "Jerry" Lawrence
                            2001 October
                         jsl@absynth.com

           http://www.cis.rit.edu/~jerry

OVERVIEW

This is a basic, tiny LISP implementation. It was created to be a configuration/logic file format for a game I am working on. It is easily extendable enough to be used for other projects as well.

This project is meant to be included within your own work. There is a sample executable that gets built that reads in from a file, and interprets it, but it is very easy to integrate this source into your own projects.

It is also very easy to add your own methods into the evaluation core.

Supported Commands

Misc

#       # foo           comment - skipped during parsing
;       ; foo           comment - skipped during parsing

A       (A)             returns the value

Variables, Functions:
set (set A B ... ) sets A to B, evaluating both. Returns B. setf (setf A B ... ) sets A to B, evaluating only B. Returns B. setq (setq x 4 y 3) same as 'setf'
defun (defun A B C) defines a function called A with parameter list B

                        and code block C.  Returns A.
        (A X Y)         Calling the above (if there were two parameters.)
                        Wrong number of parameters returns NIL w/o evaluating

enum (enum a b c) sets up N variables with incrementing values.

Numbers

+       (+ A B C)       add a list
-       (- A B C)       subtract a list
*       (* A B C)       multiply a list
/       (/ A B C)       divide a list
%       (% A B)         After A is divided by B, what's the leftover?

1+      (1+ A)          returns the number plus one
1-      (1- A)          returns the number minus one

Comparisons

<       (<  A B)        returns T if A <  B, otherwise NIL
<=      (<= A B)        returns T if A <= B, otherwise NIL
>       (>  A B)        returns T if A >  B, otherwise NIL
>=      (>= A B)        returns T if A >= B, otherwise NIL
=       (=  A B)        returns T if A == B, otherwise NIL

and     (and A B)       eval's the arguments until it hits a NIL
or      (or A B)        eval's the arguments while args are NIL
not     (not A)         returns the opposite of A (T->NIL),(NIL->T)
null    (null A)        same as 'not'

if      (if A B C)      if A is true, then B else C. if there's no C, return NIL

unless (unless A B C) unless A is true, do B, C and any others. when (when A B C) when A is true, do B, C and any others. cond (cond (A B C)) if A is true then do B,C... otherwise, try the next set select (select A B C) case statement. Evaluates 'A', then compares it to

                        the first values of lists B and C.  If they were equal,
                        the rest of the list gets evaluated, and last return 
                        gets returned.

Evaluations

eval (eval (A B)) evaluates (A B) as if it were directly input prog1 (prog1 A B C) evaluates all parts, returns the first's return value prog2 (prog2 A B C) evaluates all parts, returns the second's return value progn (progn A B C) evaluates all parts, returns the last's return value

Lists

quote   quote (A B)     returns the element instead of evaluating it
'       '(A B)          same as 'quote'

atom    (atom E)        returns T if E evaluates to an atom, not a list
equal   (equal A B)     returns T if A and B have the same structure and atoms

car     (car E)         returns the head of list E
cdr     (cdr E)         returns all but the head of list E
cons    (cons A B)      returns a appended to the head of list B
list    (list A B)      returns a list of the elements as passed in

Output

princ   (princ A B)     print out the list entries and atoms
terpri  (terpri)        print out a new line (terminate printing)

Misc

gc      (gc)            garbage collect.  Returns "T".  (does nothing)
garbage-collect         same as 'gc'

BUILD

You should be able to just type 'make' or 'gmake' or whatever your GNU make is called. The Build process depends on:

noweb literate programming toolset

If you want the document, you also need:

        pdflatex
        latex

To build the doc, type:

make docs

The build process will also generate a few sample LISP test files.

VERSION

The latest version of this should be available off of

http://www.cis.rit.edu/~jerry/Software/lithp

Be sure you're using the latest version.

LICENSE

This program is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA