Esch: Embedded Scheme


Embedded SCHeme is an implemetation of Scheme interpreter. It starts from a subset of R6RS standard, and may add features in future releases. The first goal is to make it as much compliant as R6RS standard. However, given the complexity of R6RS itself, the implementation may choose only a reasonable subset from first release. Other features may be added in the future.

The second goal of Esch is to make this implementation small enough to be embedded into other programs. The code is written in C to keep portability between compilers and operating systems.

While keeping the two above as committed goals, a third goal here is to make Esch a compiler to generate bytecode for different virtual machines. For example, it could be really nice to make Esch genreates .pyc code so the script can be executed with Python. However, this will not be implemented in a near future.

Build Esch

Esch uses SCons as build system. It allows Esch to be built cross platforms.

Esch tries to stick to C89 standard. Thus, Esch should be able to compile with any C89 compilant C compiler. The only two exceptions are: C-binding and threading. Esch uses platform-dependent libraries to implement dynamic library loading and threading.

Right now Esch supports building only on Mac. Linux and other Unix family OS should be OK but not tested. Windows build support will be added later.

To build Esch, make sure to install the following dependencies:

When everything is downloaded, do the following:

hg clone https://fuzhouch@bitbucket.org/fuzhouch/esch
cd esch

An output of build result looks like below (assume you are with Unix):

scons: Reading SConscript files ...
Build mode = release
scons: done reading SConscript files.
scons: Building targets ...
gcc -o src/esch_alloc.o -c -std=c89 -O2 -DNDEBUG -Isrc src/esch_alloc.c
gcc -o src/esch_log.o -c -std=c89 -O2 -DNDEBUG -Isrc src/esch_log.c
gcc -o src/utest/esch_t_alloc.o -c -std=c89 -O2 -DNDEBUG -Isrc src/utest/esch_t_alloc.c
gcc -o src/utest/esch_utest.o -c -std=c89 -O2 -DNDEBUG -Isrc src/utest/esch_utest.c
ar rc src/libesch.a src/esch_alloc.o src/esch_log.o
ranlib src/libesch.a
gcc -o src/esch_utest src/utest/esch_t_alloc.o src/utest/esch_utest.o -Lsrc -lesch
scons: done building targets.

Now, copy src/esch.h and src/libesch.a to your project. Start coding.

To debug Esch code, use scons mode=debug instead of scons to build project. Debug build removes optimization, enables assertion and adds additional logging support.

When everything is done, user gets two binaries:

  • A library, libesch.a. This is a library to provide core features of Scheme interpretation and core library.
  • An executable interpreter, esch. This is the interpreter and debugger to execute given Scheme script.

NOTE: The interpreter is currently under implementing.

Run Scheme scripts with Esch


Embedded Esch in C/C++



Esch v0.1

  • Implement source code structure.
  • Compelete build system. Support building on Mac.
  • Implement language parser.
    • Define variables.
    • If statement.
    • Function definition support.
    • Symbols support.
    • List support.
    • Write to standard output.
  • Implement a basic runtime engine.

Esch v1.0

  • Implement full R6RS language and library specification.