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Scheme 48

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Scheme 48
ParadigmsMulti: functional, procedural, meta
Designed byRichard Kelsey,
Jonathan Rees
DevelopersRichard Kelsey,
Jonathan Rees
First appearedMarch 1987; 37 years ago (1987-03)
Stable release
1.9.2 / 12 April 2014; 10 years ago (2014-04-12)
Typing disciplineDynamic, strong, Latent

Scheme 48 is a programming language, a dialect of the language Scheme, an implementation using an interpreter which emits bytecode.[2] It has a foreign function interface for calling functions from the language C[3] and comes with a library for regular expressions (regex),[4] and an interface for Portable Operating System Interface (POSIX).[5] It is supported by the portable Scheme library SLIB, and is the basis for the Scheme shell Scsh.[2] It has been used in academic research.[6] It is free and open-source software released under a BSD license.

It is called "Scheme 48" because the first version was written in 48 hours in August 1986.[7] The authors now[when?] say it is intended to be understood in 48 hours.[citation needed]



Scheme 48 uses a virtual machine to interpret the bytecode, which is written in a restricted dialect of Scheme called PreScheme, which can be translated to C and compiled to a native binary. PreScheme, or Pre-Scheme, is a statically-typed dialect of Scheme with the efficiency and low-level machine access of C while retaining many of the desirable features of Scheme.

Pre-scheme was quite interesting. Kelsey published a paper on it, as well, I believe. It was Scheme in the sense that you could load it into a Scheme system and run the code. But it was restrictive – it required you to write in a fashion that allowed complete Hindley-Milner static type inference, and all higher-order procedures were beta-substituted away at compile time, meaning you could *straightforwardly* translate a prescheme program into "natural" C code with C-level effiency [sic]. That is, you could view prescheme as a really pleasant alternative to C for low-level code. And you could debug your prescheme programs in the interactive Scheme development environment of your choice, before flipping a switch and translating to C code, because prescheme was just a restricted Scheme. The Scheme 48 byte-code interpreter was written in prescheme. Prescheme sort of died – beyond the academic paper he wrote, Kelsey never quite had the time to document it and turn it into a standalone tool that other people could use (Ian Horswill's group at Northwestern is an exception to that claim – they have used prescheme

— Olin Shivers, "Olin Shivers: History of T"[8]


  1. ^ R5RS claim at project website
  2. ^ a b Kelsey, Richard; Rees, Jonathan. "Scheme 48". S48.org. Retrieved 2018-12-05.
  3. ^ Kelsey, Richard; Rees, Jonathan; Sperber, Mike (10 January 2008). "The Incomplete Scheme 48 Reference Manual for release 1.8: Mixing Scheme 48 and C". S48.org. Retrieved 2018-12-05., Chapter 8 in manual for version 1.8.
  4. ^ Kelsey, Richard; Rees, Jonathan; Sperber, Mike (10 January 2008). "The Incomplete Scheme 48 Reference Manual for release 1.8: Regular Expressions". S48.org. Retrieved 2018-12-05., Chapter 5 in manual for version 1.8.
  5. ^ Kelsey, Richard; Rees, Jonathan; Sperber, Mike (10 January 2008). "The Incomplete Scheme 48 Reference Manual for release 1.8: Access to POSIX". S48.org. Retrieved 2018-12-05., Chapter 9 in manual for version 1.8.
  6. ^ Final shift for call/cc: direct implementation of shift and reset
  7. ^ Rees, Jonathan A. "JAR's Scheme 48 Page". Jonathan A. Rees. Mumble.net. Retrieved 2018-12-05.
  8. ^ Shivers, Olin. "Olin Shivers: History of T". PaulGraham.com. Retrieved 2018-12-05.