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added note about experimenting with contracts

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svn: r12088
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Robby Findler 2008-10-21 21:24:49 +00:00
parent 0ec881dc60
commit 505cc65181
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37
collects/scribblings/guide/contracts-intro.scrbl
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@ -193,3 +193,40 @@ services, it also demands the client to deliver
something. This kind of thing happens when a module exports
a function, an object, a class or other values that enable
values to flow in both directions.
@ctc-section{Experimenting with examples}
All of the contracts and module in this chapter (excluding those just
following) are written using the standard @tt{#lang} syntax for
describing modules. Thus, if you extract examples from this chapter in
order to experiment with the behavior of the contract system, you
would have to make multiple files.
To rectify this, PLT Scheme provides a special language, called
@tt{scheme/load}. The contents of such a module is other modules (and
@scheme[require] statements), using the parenthesized syntax for a
module. For example, to try the example earlier in this section, you
would write:
@schememod[
scheme/load
(module m scheme
(define amount 150)
(provide/contract [amount (and/c number? positive?)]))
(module n scheme
(require 'm)
(+ amount 10))
(require 'n)]
Each of the modules and their contracts are wrapped in parenthesis
with the @scheme[module] keyword at the front. The first argument to
@scheme[module] should be the name of the module, so it can be used in
a subsequent @scheme[require] statement (note that in the
@scheme[require], the name of the module must be prefixed with a
quote). The second argument to @scheme[module] is the language (what
would have come lang @tt{#lang} in the usual notation), and the
remaining arguments are the body of the module. After all of the
modules, there must a @scheme[require] to kick things off.