[r6rs-discuss] [Formal] fenders should be dropped from syntax-rules

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This message is a formal comment which was submitted to formal-comment_at_r6rs.org, following the requirements described at: http://www.r6rs.org/process.html
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Name: David Van Horn
Email: dvanhorn_at_cs.brandeis.edu
Type: Simplification
Priority: Major
R6RS component: Macros
Version of the report: 5.91
Summary of the issue
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The <fender> production should be removed from the language of 
syntax-rules forms.
Full description
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Allowing fenders in syntax-rules significantly complicates the semantics 
of syntax-rules-based transformations, introducing phase distinctions 
where there used to be none and allowing the use of arbitrary Scheme 
code in what was once a simple rewritting specification.  The 
complications add essentially no practical benefit without also using 
the (r6rs syntax-case) library.  With the inclusion of syntax-case in 
R6RS, when fenders are needed, they may be used and a derived form 
syntax-rules/fenders can be defined using (r6rs syntax-case), but this 
makes it explicit that the enhanced facilities provided by syntax-case 
are being relied upon.