3 R5RS Module Language

As a library, r5rs provides the syntactic forms and procedures defined by R5RS. When used as a language via #lang, the program is read with the following parameterizations:

(read-case-sensitive #f)

(read-accept-infix-dot #f)

(read-curly-brace-as-paren #f)

(read-square-bracket-as-paren #f)

The r5rs bindings can be imported into a top-level environment, and then evaluation in that top-level environment corresponds to R5RS. Use (namespace-require/copy 'r5rs) with an empty namespace to maximize conformance with R5RS; Using (namespace-require 'r5rs), in contrast, creates primitive bindings as imports, which is the same as using plt-r5rs without the --no-prim flag. More simply, use (scheme-report-environment 5). See also r5rs/init, which sets reader and printer parameters to increase conformance.

Using r5rs via #lang creates a module whose body is implemented with an R5RS-like language. The main difference from R5RS is that, as a module language, r5rs does not allow redefinition of top-level bindings, and expressions evaluated through load and eval cannot automatically access bindings defined within the module.

Changed in version 6.0.1.4 of package r5rs-lib: When an identifier bound by letrec is referenced before it is initialized, an exception is raised, instead of producing #<undefined>.

3.1 Non-R5RS Bindings from r5rs

In addition to the bindings defined by R5RS, the r5rs library provides the following bindings from racket/base (which are not legal identifiers in R5RS syntax, so there is no danger of collisions in R5RS programs):

#%app #%datum #%top #%top-interaction #%require #%provide

It also provides racket’s #%plain-module-begin as #%module-begin. Note that #%require can be used to import Racket libraries into an otherwise R5RS program, and #%provide can be used to export from a module that is implemented in an R5RS-like language.

3.2 Notes on R5RS Functions

The cons of r5rs corresponds to racket/base’s mcons. Similarly, cdr is mcdr, and map is compatibility/mlist’s mmap, and so on.

An R5RS environment is implemented as a racket/base namespace. Also, relative to racket/base, the expr passed to eval is constructed using mutable pairs.

The scheme-report-environment function returns a namespace containing the bindings of r5rs. Procedure values are installed into the namespace using namespace-require/copy, so that they can be redefined.

The null-environment function returns a namespace containing the syntactic forms of r5rs, not including #%module-begin (which is not useful outside of a module).