Shen/Scheme, a Scheme port of the Shen language

Shen is a portable functional programming language by Mark Tarver that offers

pattern matching,
λ calculus consistency,
macros,
optional lazy evaluation,
static type checking,
an integrated fully functional Prolog,
and an inbuilt compiler-compiler.

shen-scheme is a port of the Shen language that runs on top of Sheme implementations.

Right now the following implementations are supported:

chez-scheme

The following implementations were supported in version 0.15, but are not supported since version 0.16. Support may be added back in future releases.

Binaries

Starting with version 0.18, binaries are provided for Windows, Linux and OSX. See releases.

OSX users can also use homebrew to install Shen/Scheme:

$ brew install Shen-Language/homebrew-shen/shen-scheme
==> Installing shen-language/shen/shen-scheme
==> Downloading https://github.com/tizoc/shen-scheme/releases/download/0.17/shen-scheme-0.17-src.tar.gz
Already downloaded: /Users/bruno/Library/Caches/Homebrew/shen-scheme-0.17.tar.gz
==> Downloading https://github.com/cisco/ChezScheme/archive/v9.5.tar.gz
Already downloaded: /Users/bruno/Library/Caches/Homebrew/shen-scheme--chezscheme-9.5.tar.gz
==> make install prefix=/usr/local/Cellar/shen-scheme/0.17
  /usr/local/Cellar/shen-scheme/0.17: 7 files, 2.8MB, built in 1 minute 16 seconds

Building

Building from the source distribution

Running make should do the job. It will download and compile Chez under the _build directory, and then the shen-scheme binary and shen.boot boot files.

make prefix=/opt/shen-scheme # optional prefix, defaults to /usr/local

then to install:

make install

This will install the shen-scheme binary to $(prefix)/bin/shen-scheme and the boot file to $(prefix)/lib/shen-scheme/shen.boot.

To build on Windows, an environment with curl, 7zip, make and Visual Studio 2017 is needed (all installable with chocolatey).

Building from scratch

This step is only necessary if cloning from this repository, the release tarballs include pregenerated .scm files.

To build from source, obtain a copy of the Shen kernel distribution and copy the .kl files to the kl/ directory of shen-scheme. Then with a working Shen implementation do:

(load "scripts/build.shen")
(build program "shen-scheme.scm")

This will produce .scm files in the compiled/ directory and a shen-scheme.scm file in the current directory.

After doing this the procedure is the same as building from the source distribution.

Running

shen-scheme will start the Shen REPL. shen-scheme script <some shen file> will run a script. shen-scheme eval <shen expression> will evaluate an expression.

Home and Boot file search path

Shen/Scheme will use as its home directory a path relative to the executable: ../lib/shen-scheme. For example, if the executable is /usr/local/bin/shen-bin then the home directory will be /usr/local/lib/shen-scheme. This can be overriden by the SHEN_SCHEME_HOME environment variable.

By default, the boot file will be loaded from <shen-scheme-home>/shen.boot, but the location can be overriden with the SHEN_SCHEME_BOOT environment variable.

Native Calls

Scheme functions live under the scm namespace (scm. prefix), and the names need to be wrapped with the foreign form in calls. For example: ((foreign scm.write) [1 2 3 4]) invokes Scheme's write function with a list as an argument.

Because Scheme functions can have variable numbers of arguments and the code passed to scm. is not preprocessed, any imported function that is intended to support partial application has to be wrapped with a defun:

(0-) (defun my-for-each (F L) ((foreign scm.for-each) F L))
my-for-each

(1-) (my-for-each (/. X (do (print (+ X X)) (nl))) [1 2 3 4 5])
2
4
6
8
10
0

(2-) (my-for-each (function print))
#<procedure>

Literal Scheme Code

Scheme code can be compiled as-is with the scm. special form that takes a string with Scheme code as an argument.

Example:

(0-) ((foreign scm.) "(+ 1 2)")
3

(1-) ((foreign scm.) "(begin (display c#34;testc#34;) (newline))")
test
#<void>

(2-) ((foreign scm.) "(list #t #f (quote symbol) 'symbol)")
[true false symbol symbol]

Importing bindings from Scheme modules

import expressions are supported through the scm. prefix. Names will be imported under the scm. namespace.