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97 lines
5 KiB
Markdown
97 lines
5 KiB
Markdown
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# Cheap and fast R7RS Scheme Interpreter
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SKINT is a portable interpreter for the R7RS Scheme programming language.
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It can be built from five C source files (10K lines of code) with a single command. There is no distributives or packages;
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just compile the source files with your favorite C compiler, link them with the standard C runtime libraries,
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and you're done. For some platforms, precompiled binaries are available (please see [releases](https://github.com/false-schemers/skint/releases)).
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## Installation
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Here's how you can compile SKINT on a unix box using GCC:
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```
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gcc -o skint [skint].c -lm
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```
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Some compilers link `<math.h>` library automatically, some require explicit option like `-lm` above. It can be built on 32-bit
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and 64-bit systems.
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For *much* better performance (especially in floating-point calculations) you may pick another compiler, add optimization flags
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and some SKINT-specific options, e.g.:
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```
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clang -o skint -O3 -D NDEBUG -D NAN_BOXING [skint].c -lm
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```
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The NAN_BOXING option assumes that the upper 16 bits of heap pointers are zero (48-bit address space). It is recommended to use this
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option on 64-bit systems that guarantee this.
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The resulting interpreter has no dependencies (except for C runtime and standard -lm math library) and can be run from any location.
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If linked statically, it can be easily moved between systems with the same ABI.
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For a more traditional install, please follow the instructions below. Skint will be
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installed as `/usr/local/bin/skint` command.
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```
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git clone https://github.com/false-schemers/skint.git
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cd skint
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make
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make test
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sudo make install
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```
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## Scheme Compatibility
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SKINT is true to basic Scheme principles -- it features a precise garbage collector, supports proper tail recursion, `call/cc`,
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`dynamic-wind`, multiple return values, has a hygienic macro system, and a library system. It is almost fully compatible
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with R7RS-small, but has the following known limitations and deviations from the standard:
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* fixnums are 30 bit long, flonums are doubles
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* no support for bignums/rational/complex numbers
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* no support for Unicode; strings are 8-bit clean, use system locale
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* source code literals cannot be circular (R7RS allows this)
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Some features of the R7RS-Small standard are not yet implemented or implemented in a simplified or non-conforming way:
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* `read` procedure is always case-sensitive (all ports operate in no-fold-case mode)
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* `#!fold-case` and `#!no-fold-case` directives have no effect
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* `include` and `include-ci` forms work in case-sensitive mode
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* `current-jiffy` and `jiffies-per-second` return inexact integers
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* `current-second` is defined as C `difftime(time(0), 0)+37`
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Here are some details on SKINT's interactive Read-Eval-Print-Loop (REPL) and evaluation/libraries support:
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* `read` supports R7RS notation for circular structures, but both `eval` and `load` reject them
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* all R7RS-small forms are available in the built-in `(skint)` library and REPL environment
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* `-I` and `-A` command-line options extend library search path; initial path is `./`
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* `cond-expand` checks against `(features)` and available libraries
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* `environment` may dynamically fetch external library definitions from `.sld` files
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* both `eval` and `load` accept optional environment argument
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* command-line options can be shown by running `skint --help`
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* both `import` and `define-library` forms can be entered interactively into REPL
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* REPL supports single-line “comma-commands” — type `,help` for a full list
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* on Un*x-like systems, interactive use of skint with line exiting requires external readline wrapper
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such as [rlwrap](https://github.com/hanslub42/rlwrap)
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Please note that SKINT's interaction environment exposes bindings for all R7RS-small procedures
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and syntax forms directly, so there is no need to use `import`. All R7RS-small libraries are built-in and
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do not rely on any external .sld files.
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## Origins
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Parts of SKINT's run-time system and startup code are written in [#F](https://github.com/false-schemers/sharpF),
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a language for building Scheme-like systems. Its #F source code can be found there in `precursors` directory:
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[skint/pre](https://github.com/false-schemers/skint/tree/main/pre)
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SKINT's hygienic macroexpander is derived from Al Petrofsky's EIOD 1.17 (please see the t.scm file for the original copyright info).
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SKINT's VM and compiler follow the stack machine approach described in “Three Implementation Models for Scheme” thesis by R. Kent Dybvig
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([TR87-011](https://www.cs.unc.edu/techreports/87-011.pdf), 1987).
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Supporting library code comes from #F's [LibL library](https://raw.githubusercontent.com/false-schemers/sharpF/master/lib/libl.sf).
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## Family
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Please see [SIOF](https://github.com/false-schemers/siof) repository for a single-file R7RS-small interpreter. It is
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more portable and easier to build, but is less complete and runs significantly slower.
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