Source code can be found at: https://github.com/samth/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.
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 [email protected] (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 [email protected] (import drscheme:tool^) (export drscheme:tool-exports^) (define (phase1) (message-box "phase1")) (define (phase2) (message-box "phase2")))]))
#lang racket/base (require version-case (for-syntax racket/base)) (printf "~a~n" (version-case [(version<= (version) "4") 'huh?] [else 'ok]))
(version-case [test code ...] ... [else code ...])
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)).
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.