Libraries

The twelve R7RS libraries a file may import, and what each provides. Every name has its own page in the Reference. A file that opens with (import ...) (see Syntax) sees only the libraries it names; a file with none sees all twelve, plus the Structure and Interpretation of Computer Programs (SICP)-compatibility names.

Library	Provides
(scheme base)	The core: numbers, booleans, pairs and lists, symbols, characters, strings, vectors, bytevectors, control, exceptions, ports -- string and bytevector ports, the current ports -- and input and output; its syntax is on Syntax
(scheme write)	`display` and `write`
(scheme read)	`read`
(scheme char)	Unicode character classes, case mappings and case-insensitive comparisons
(scheme inexact)	Transcendental functions and the float predicates
(scheme cxr)	The three- and four-deep `car`/`cdr` compositions
(scheme lazy)	Promises
(scheme case-lambda)	`case-lambda`
(scheme process-context)	`exit` and `emergency-exit` only
(scheme eval)	`eval` and `environment` -- see eval
(scheme repl)	`interaction-environment`
(scheme file)	File ports, `file-exists?` and `delete-file`

Every input and output procedure takes an optional port argument and uses the current port without one. The current ports are parameter objects, so parameterize redirects them. A file port is opened on a file name -- see (scheme file).

"captured (1 \"two\")"
((a b) 42 #t)

500000500000
4
3

Printing

write and display write a circular list or vector with datum labels, #0=(a b c . #0#); structure shared without a cycle is written out each time.

An exact argument with an exact answer stays exact, and a flonum prints positionally below 1e21 and with an exponent from there (and below 1e-6):

(4 1/2 1.4142135623730951 1 0)
(123456789.123 1e21 0.000001 1.5e-7 +inf.0)

Libraries of your own

A program splits into libraries with define-library: at the beginning of the file, before its imports, or in a file of its own that (import (shapes circle)) finds as shapes/circle.sld beside the program. A library's names are private unless it exports them. include puts a file's contents where it stands; both are read when the program is, so a compiled program needs none of the files at run time.

; file: shapes/circle.sld
(define-library (shapes circle)
  (export area)
  (import (scheme base))
  (begin
    (define pi 314/100)
    (define (area r) (* pi r r))))

(314 3)

Features

cond-expand picks code by the features of the implementation and the libraries it has, when the program is read: a program written for several Scheme systems runs here, and the branches it does not take are never compiled.

rontolisp