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Original author(s)George J. Carrette
Stable release
3.63 / April 27, 2008 (2008-04-27)
Written inC
Operating systemCross-platform
TypeProgramming language
LicenseGNU Lesser General Public License

Scheme In One Defun (or Scheme In One Day) is a small-footprint implementation of the Scheme programming language, written in C and designed to be embedded inside C programs. It is notable for being perhaps the smallest practical implementation of a Lisp-like language. It was originally written by George J. Carrette.


  • SIOD implements the original version of Scheme from the Lambda Papers, but it does not implement any of the modern language standards.
  • SIOD represents a very early use of conservative garbage collection in a Lisp interpreter, a technique which was later copied by SCM and Guile.
  • Compilation is implemented by emitting a fixed machine code prologue followed by a fast-loading binary representation of the parse tree to be interpreted.


  • GIMP used SIOD as its primary extension language, Script-Fu, until version 2.4 was released.[1]
  • SIAG (Scheme in a grid) is a spreadsheet application using SIOD as a base.
  • Festival Speech Synthesis System uses SIOD as its underlying command interpreter. [2]


  1. ^ "GIMP - Script-Fu Migration Guide". Retrieved November 12, 2011.
  2. ^ "CSTR Festival Speech Synthesis System". Retrieved May 26, 2013.

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