R7RS Compatibility

Sigil implements most of R7RS Small, with practical extensions. This page lists what works, what works with differences, and what is missing, as of Sigil 0.22.8.

Where R7RS Names Live

Sigil does not provide the (scheme ...) library names: (import (scheme base)) fails with "library not found". The R7RS procedures live in Sigil's own modules:

• (sigil core), which every program and library sees without an import, has most of (scheme base), (scheme case-lambda), (scheme char), (scheme lazy) and (scheme write).
• (sigil io) has the port procedures that read and write characters, strings, bytes and bytevectors, string and bytevector ports, and file ports.
• (sigil math) has (scheme inexact): sqrt, exp, log, the trigonometric functions, finite?, infinite? and nan?. It also re-exports the (scheme base) math procedures that core has, such as floor and quotient.
• (sigil string) has the case-insensitive string-ci comparisons.
• (sigil process), (sigil time) and (sigil fs) have the process-context, time and file-system procedures.

Tables on this page say "in (sigil io)" and so on where a name is not in core.

R7RS Libraries

Import Modifiers

All R7RS import set modifiers are supported in both define-library and top-level import forms:

Modifiers compose through nesting, e.g. (prefix (only (sigil math) sqrt exp) m:).

Intentionally Omitted

Sigil prioritizes practical utility over numeric tower completeness:

No Exact Rationals

Sigil has integers (fixnums and bignums) and floating-point numbers, but no rational number type:

;; Other Schemes:
(/ 1 3)  ; => 1/3 (exact rational)

;; Sigil:
(/ 1 3)  ; => 0.333... (inexact float)

numerator, denominator and rationalize work on floats and return inexact results for fractional values.

No Complex Numbers

The (scheme complex) library is not provided. complex? and real? are the same as number?.

No R5RS Compatibility Library

The (scheme r5rs) library is not provided. The R5RS names exact->inexact and inexact->exact are in core.

(scheme base) Coverage

Control Flow

Procedures

Numeric

Lists and Pairs

Booleans and Symbols

Strings

Vectors

Bytevectors

Error Objects

I/O

Notes on write:

• It prints floats with 6 significant digits ((write (/ 1.0 3)) prints 0.333333), so a written float may not read back as the same number. number->string keeps full precision.
• It uses datum labels for shared structure even when there is no cycle: a list holding the same sublist twice prints as (#0=(1 2) #0#). write-simple prints no labels.
• It writes printable non-ASCII text as itself, so (write "λ") prints "λ". Control characters and invisible formatting characters (zero-width spaces, bidi controls, the byte order mark) print as one escape per character, such as \x1B; or \x202E;, and a byte that is not valid UTF-8 as \x<byte>;, which reads back as the character with that number. Everything else write prints for a string reads back as the same string. Before 0.22.13 it wrote each UTF-8 byte as \xHH with no ;, which read rejected.
• #\λ reads as one character; a non-ASCII character is written as #\x3BB.

Records

Macros

(scheme char) Coverage

Feature Identifiers

The features procedure returns a list of supported feature identifiers for use with cond-expand:

(features)
; => (r7rs sigil linux posix unix x86-64 lp64 64bit little-endian)

Available features:

• r7rs - R7RS compliance
• sigil - Sigil implementation
• Platform: linux, darwin, windows, freebsd, openbsd, netbsd
• POSIX: posix, unix (on Unix-like systems)
• Architecture: x86-64, aarch64, arm, i386, riscv
• Data model: ilp32, lp64
• Word size: 32bit, 64bit
• Endianness: little-endian, big-endian

Sigil Extensions

Sigil provides additional features beyond R7RS:

Pattern Matching

(import (sigil match))

(match value
  ((a b c) (list a b c))
  ((x . rest) rest)
  (_ 'default))

Keywords

Keyword arguments in procedures:

(define (greet name: "World" times: 1)
  (do ((i 0 (+ i 1)))
      ((= i times))
    (display "Hello, ")
    (display name)
    (newline)))

(greet name: "Sigil" times: 3)

Additional Modules

• (sigil core) - Extended list operations, filter-map, fold-left, etc.
• (sigil json) - JSON parsing and generation
• (sigil http) - HTTP client and server
• (sigil socket) - TCP/UDP networking
• (sigil process) - Process spawning
• (sigil path) - Path manipulation
• (sigil fs) - File system operations
• (sigil time) - Date and time
• (sigil channels) - CSP-style concurrency

See the Library Reference for complete documentation.

Porting from Other Schemes

Replace (scheme ...) imports with Sigil modules. Most code needs no import at all for (scheme base), because (sigil core) is always available; add (sigil io), (sigil math) or (sigil string) for the names listed above.

From Guile

Guile modules map directly:

;; Guile
(use-modules (ice-9 match))

;; Sigil
(import (sigil match))

From Racket

Racket's #lang is not supported. Convert to standard module syntax:

;; Racket
#lang racket
(define (foo x) x)

;; Sigil
(define-library (my-module)
  (export foo)
  (import (sigil core))
  (begin
    (define (foo x) x)))

From Chicken

SRFI libraries are not bundled: (import (srfi srfi-1)) fails with "library not found". Core has list procedures with SRFI-1 names, but some differ from SRFI-1:

• fold calls its procedure as (proc acc elem), so (fold cons '() '(1 2 3)) gives (((() . 1) . 2) . 3).
• remove takes an item to remove, not a predicate.
• any returns #t, not the true value its predicate returned.