Library syntax
A library definition takes the following form:
(define-library {library-name}
{library declaration} ...)
{library name} is a list whose members are identifiers and exact non-negative integers. It is used to
identify the library uniquely when importing from other programs or
libraries.
Libraries whose first identifier is scheme are reserved for use by this
report and future versions of this report.
Libraries whose first identifier is srfi are reserved for libraries
implementing Scheme Requests for Implementation.
It is inadvisable, but not an error, for identifiers in library names to
contain any of the characters | \ ? * < " : > + [ ] /
or control characters after escapes are expanded.
A library declaration is any of:
(export {export spec} ...)
(import {import set} ...)
(begin {command or definition} ...)
(include {filename1} {filename2} ...)
An export declaration specifies a list of identifiers which
can be made visible to other libraries or programs.
An export spec takes one of the following forms:
{identifier}
(rename {identifier1} {identifier2})
In an export spec, an identifier names a single
binding defined within or imported into the library, where the
external name for the export is the same as the name of the binding
within the library. A rename spec exports the binding
defined within or imported into the library and named by
{identifier1} in each ({identifier1} {identifier2} pairing, using
{identifier2} as the external name.
An import declaration provides a way to import the identifiers
exported by another library. It has the same syntax and semantics as
an import declaration used in a program or at the REPL (see section 5.2).
The begin and include declarations are
used to specify the body of
the library. They have the same syntax and semantics as the corresponding
expression types.
This form of begin is analogous to, but not the same as, the
two types of begin defined in section 4.2.3.
When a library is loaded, its expressions are executed
in textual order.
If a library's definitions are referenced in the expanded form of a
program or library body, then that library must be loaded before the
expanded program or library body is evaluated. This rule applies
transitively. If a library is imported by more than one program or
library, it may possibly be loaded additional times.
Similarly, during the expansion of a library (foo), if any syntax
keywords imported from another library (bar) are needed to expand
the library, then the library (bar) must be expanded and its syntax
definitions evaluated before the expansion of (foo).
Regardless of the number of times that a library is loaded, each
program or library that imports bindings from a library must do so from a
single loading of that library, regardless of the number of import
declarations in which it appears.
That is, (import (only (foo) a)) followed by (import (only (foo) b))
has the same effect as (import (only (foo) a b)).
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