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README.md

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:

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.

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.

It is recommented that Windows users download the binary distribution.

OSX users can 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 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.

Boot file search path

If the environment variable SHEN_BOOTFILE_PATH has a value, it will be used as the path to the boot file to load. If not, it will be searched on at the location defined by the compile-time variable DEFAULT_BOOTFILE_PATH. If the value of DEFAULT_BOOTFILE_PATH is NULL, then a shen.boot file placed at the same directory as the shen-scheme executable will be loaded.

On Windows builds DEFAULT_FILE_PATH defaults to NULL, otherwise it defaults to $(prefix)/lib/shen-scheme/shen.boot. It can be customized at build time by setting the bootfile_path variable when calling make:

make bootfile_path=NULL # Load from same directory as executable
make bootfile_path=\"/home/me/shen/boot\" # Load from custom location

Native Calls

Scheme functions live under the scm namespace (scm. prefix). For example: (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) (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-) (scm. "(+ 1 2)")
3

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

(2-) (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.

Example:

(1-) (scm.import (rename (rnrs) (+ add-numbers)))
#<void>

(2-) (scm.add-numbers 1 2 3 4)
10

License