This site is a static rendering of the Trac instance that was used by R7RS-WG1 for its work on R7RS-small (PDF), which was ratified in 2013. For more information, see Home.

Source for ticket #106

cc


    
changetime

    
2011-01-24 06:54:00

    
component

    
WG1 - Core

    
description

    
As discussed in

  https://groups.google.com/group/scheme-reports-wg1/browse_thread/thread/99c05dcb6a500183

users invariably want some way to conditionally
select code depending on the implementation and/or
feature set available.  SRFI-0 provides `cond-expand`,
R6RS implementations informally provide a library
naming hack, and numerous other personal hacks exist.

Do we want to include something along these lines
in WG1 Scheme?


    
id

    
106

    
keywords

    

    
milestone

    

    
owner

    
alexshinn

    
priority

    
major

    
reporter

    
alexshinn

    
resolution

    
fixed

    
severity

    

    
status

    
closed

    
summary

    
conditional code selection

    
time

    
2010-11-30 13:04:16

    
type

    
defect

    
Changes

    
Change at time 2011-01-24 06:54:00

    
author

    
cowan

    
field

    
comment

    
newvalue

    
WG1 decided to go with CondExpandCowan.

    
oldvalue

    
3

    
raw-time

    
1295823240000000

    
ticket

    
106

    
time

    
2011-01-24 06:54:00

    
Change at time 2011-01-24 06:54:00

    
author

    
cowan

    
field

    
resolution

    
newvalue

    
fixed

    
oldvalue

    

    
raw-time

    
1295823240000000

    
ticket

    
106

    
time

    
2011-01-24 06:54:00

    
Change at time 2011-01-24 06:54:00

    
author

    
cowan

    
field

    
status

    
newvalue

    
closed

    
oldvalue

    
new

    
raw-time

    
1295823240000000

    
ticket

    
106

    
time

    
2011-01-24 06:54:00

    
Change at time 2010-12-17 15:51:09

    
author

    
arcfide

    
field

    
comment

    
newvalue

    
I want to mention [http://www.scheme.com/csug8/syntax.html#./syntax:h9 meta-cond] which I think is a particularly nice and general solution. I think we could make it work.

    
oldvalue

    
2

    
raw-time

    
1292572269000000

    
ticket

    
106

    
time

    
2010-12-17 15:51:09

    
Change at time 2010-11-30 16:04:44

    
author

    
medernac

    
field

    
comment

    
newvalue

    
Definitely yes, we need a standard way to inspect the availability
of optional features and select code accordingly. There already are many existing proposals, this is either a module feature or a meta-language feature:
 
* SRFI-0 defines a registry of "feature identifiers" and a 'cond-expand' form.
* SRFI-55 has 'require-extension'
* SLIB has 'require / provided? / provide' forms
* Modules systems have their import mechanism
* There are also configuration languages such as Scheme48, Racket, etc.



    
oldvalue

    
1

    
raw-time

    
1291104284000000

    
ticket

    
106

    
time

    
2010-11-30 16:04:44