version-case: conditionally compile code based on current version number

Danny Yoo <[email protected]>

Source code can be found at: https://github.com/dyoo/version-case.

This library provides support for conditionally compiling code based on the version of Racket. One common application of this module is to write compatibility bindings.

1 Example

The following example shows how one can write unit code that works with both the old and new unit libraries.

(module some-sample-unit-code mzscheme

(require (planet "version-case.ss" ("dyoo" "version-case.plt" 1))

(lib "mred.ss" "mred"))

(version-case

[(version<= (version) "360")

(printf "old unit code~n")

(require (lib "tool.ss" "drscheme")

(lib "unitsig.ss"))

(define tool@

(unit/sig drscheme:tool-exports^

(import drscheme:tool^)

(define (phase1)

(message-box "phase1"))

(define (phase2)

(message-box "phase2"))))]

[else

(printf "new unit code~n")

(require (lib "tool.ss" "drscheme")

(lib "unit.ss"))

(define-unit tool@

(import drscheme:tool^)

(export drscheme:tool-exports^)

(define (phase1)

(message-box "phase1"))

(define (phase2)

(message-box "phase2")))]))

2 Usage

3 Gotchas

The tests are done at compile time. If the language of your module doesn’t include compile-time bindings for function application, you may see funny error messages. For example, scheme/base doesn’t automatically provide the necessary compile-time bindings, so if you use version-case with it, you also need to do a (require (for-syntax scheme/base)).

4 Thanks

Special thanks to Carl Eastlund providing the implementation that doesn’t use eval, and for feedback. Thanks also to Ambjorn Elder for noticing a bug regarding the use of syntax-case within a version-case’s body.