88 lines
3.1 KiB
Racket
88 lines
3.1 KiB
Racket
#reader(lib "docreader.ss" "scribble")
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@require[(lib "manual.ss" "scribble")]
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@require[(lib "eval.ss" "scribble")]
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@require["guide-utils.ss"]
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@title{Module Syntax}
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The @litchar{#module} at the start of a module file begins a shorthand
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for a @scheme[module] form, much like @litchar{'} is a shorthand for a
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@scheme[quote] form. Unlike @litchar{'}, the @litchar{#module}
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shorthand does not work well in a REPL, in part because it must be
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terminated by an end-of-file, but also because the longhand expansion
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of @litchar{#module} depends on the name of the enclosing file.
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@;------------------------------------------------------------------------
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@section{The @scheme[module] Form}
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The longhand form of a module declaration, which works in a REPL as
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well as a file, is
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@specform[
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(module name-id initial-module-path
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decl ...)
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]
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where the @scheme[_name-id] is a name for the module,
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@scheme[_initial-module-path] is an initial import, and each
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@scheme[_decl] is an import, export, definition, or expression. In
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the case of a file, @scheme[_name-id] must match the name of the
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containing file, minus its directory path or file extension.
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The @scheme[_initial-module-path] is needed because even the
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@scheme[require] form must be imported for further use in the module
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body. In other words, the @scheme[_initial-module-path] import
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bootstraps the syntax available in the body. The most commonly used
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@scheme[_initial-module-path] is @scheme[(lib "big/lang.ss")], which
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supplies most of the bindings described in this guide, including
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@scheme[require], @scheme[define], and @scheme[provide].
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For example, the @file{cake.ss} example of the
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@seclink["guide:module-basics"]{previous section} could be written as
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@schemeblock[
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(module cake (lib "big/lang.ss")
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(provide print-cake)
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(define (print-cake n)
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(printf " ~a \n" (make-string n #\.))
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(printf " .-~a-.\n" (make-string n #\|))
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(printf " | ~a |\n" (make-string n #\space))
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(printf "---~a---\n" (make-string n #\-))))
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]
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Furthermore, this @scheme[module] form can be evaluated in a REPL to
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declare a @scheme[cake] module that is not associated with any file.
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@;------------------------------------------------------------------------
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@section{The @schememodfont{#module} Shorthand}
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Unlike @litchar{'}, there is no fixed syntax for the body of a
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@litchar{#module} shorthand. In general, the syntax is determined by
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the language name that follows @litchar{#module}.
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In the case of @schememodfont{#module} @schememodname[big], the syntax
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is
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@schememod[
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big
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_decl ...]
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which reads the same as
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@schemeblock[
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(module _name (lib "big/lang.ss")
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_decl ...)
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]
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where @scheme[_name] is derived from the name of the file that
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contains the @schememodfont{#module} form.
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The @schememodfont{#module} @scheme[little] form has the same syntax
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as @schememodfont{#module} @schememodname[big], except that the
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longhand expansion uses @scheme[(lib "little/lang.ss")] instead of
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@scheme[(lib "big/lang.ss")]. The @schememodfont{#module}
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@scheme[honu] form, in contrast, has a completely different syntax
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that doesn't even look like Scheme, and which we do not attempt to
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describe in this guide.
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