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Source for wiki RedefiningSyntax version 1

author

cowan

comment

ipnr

198.185.18.207

name

RedefiningSyntax

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text

I've been poking around the usual list of Schemes, trying to find out
what the behavior is when an identifier is defined as a value and then
redefined as syntax.  For example:

{{{
        (define (noodle) (foodle))
        (define (foodle) 23)
        (noodle) => ??
        
        (define-syntax foodle (syntax-rules ()
          ((foodle) 17)))
        (noodle) => ??
        
        (define (noodle) (foodle))
        (noodle) => ??
}}}

I tested Racket, Gauche, MIT, Chicken, Bigloo, Scheme48/scsh, Guile 2.0,
Kawa, SISC, Chibi, Chez, SCM, !IronScheme, Ikarus, Larceny, Ypsilon, Mosh,
STklos, and Scheme 9.

All the implementations behave the same way on the first and third calls
to `noodle`, returning 23 and 17 respectively.  The first definition of
`noodle` refers to `foodle`, which is undefined, and is therefore assumed to
be a variable.  (Some but not all Schemes print a warning at this point.)

The second definition of `noodle` refers to the current (syntax) definition
of `foodle`.  All but Guile and Chibi also return 23 on the second call to
noodle, ignoring the syntax definition.  Guile and Chibi, however, signal
an error to the effect that a macro was invoked where a function was expected.

time

2012-05-17 04:52:20