MiniLisp

So many years working with lush have taken their toll. There are many things I really dislike doing in C or C++ when I know how easy they would be in Lisp.

At some point I decided to simply write a C++ library to handle the basic lisp data structure: S-expressions. The implementation fits in a single C++ file, including a garbage collector and a pretty printer. The full documentation is available as comments in the header file miniexp.h

MiniExp handles four basic types of S-expressions:

• Integers, in range <latex>[-2^{29}\cdots 2^{29}-1]</latex>.
• Symbols, which are small strings represented by a unique handle.
• Pairs, which are the basic components of lists.
• Objects, which encapsulate any C++ object derived from class miniobj_t

Examples:

minivar_t a_symbol = miniexp_symbol("foo");
minivar_t a_number = miniexp_number(23);
minivar_t a_list = miniexp_cons(a_symbol, miniexp_cons(a_number, miniexp_nil));
minivar_t an_object = miniexp_string("Strings are implemented as objects.");

The type of the S-expression is miniexp_t. But we often store them into variables of type minivar_t. The difference is garbage collection. The garbage collector preserves all S-expressions stored in a minivar_t and all S-expressions recursively pointed by preserved S-expresssions.

To print a S-expression, one could write something like:

if (miniexp_numberp(exp))
  printf("%d", miniexp_to_int(exp));
else if (miniexp_symbolp(exp))
  printf("%s", miniexp_to_name(exp));
else if (miniexp_consp(exp))
  ....

But there is an easier way:

miniexp_print(exp);

and a prettier way:

miniexp_pprint(exp, 72);  // 72 is the target number of columns

You can also read S-expressions from the standard input

minivar_t exp = miniexp_read();

See the documentation in file miniexp.h for more details.

Both MiniExp and MiniLisp are available in the DjVu CVS repository.

• miniexp.h
• miniexp.cpp
• minilisp

But it might be simpler to download the tarball here: minilisp-1.0.tar.gz