14.5 Whole-module Signatures and Units

In programs that use units, modules like "toy-factory-sig.rkt" and "simple-factory-unit.rkt" are common. The racket/signature and racket/unit module names can be used as languages to avoid much of the boilerplate module, signature, and unit declaration text.

For example, "toy-factory-sig.rkt" can be written as

#lang racket/signature

build-toys  ; (integer? -> (listof toy?))

repaint     ; (toy? symbol? -> toy?)

toy?        ; (any/c -> boolean?)

toy-color   ; (toy? -> symbol?)

The signature toy-factory^ is automatically provided from the module, inferred from the filename "toy-factory-sig.rkt" by replacing the "-sig.rkt" suffix with ^.

Similarly, "simple-factory-unit.rkt" module can be written

#lang racket/unit

(require "toy-factory-sig.rkt")

(import)

(export toy-factory^)

(printf "Factory started.\n")

(define-struct toy (color) #:transparent)

(define (build-toys n)

(for/list ([i (in-range n)])

(make-toy 'blue)))

(define (repaint t col)

(make-toy col))

The unit simple-factory@ is automatically provided from the module, inferred from the filename "simple-factory-unit.rkt" by replacing the "-unit.rkt" suffix with @.