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[Chicken-janitors] Re: #505: permit user-defined read-syntax to restart

From: Chicken Trac
Subject: [Chicken-janitors] Re: #505: permit user-defined read-syntax to restart the reader
Date: Thu, 17 Feb 2011 23:37:12 -0000

#505: permit user-defined read-syntax to restart the reader
  Reporter:  zbigniew        |       Owner:  zbigniew             
      Type:  enhancement     |      Status:  new                  
  Priority:  minor           |   Milestone:  4.7.0                
 Component:  core libraries  |     Version:  4.6.x                
Resolution:                  |    Keywords:  don't fear the reader

Comment(by zbigniew):

 Here's another possibility which I think is cleaner.  It adds new starred
 variants of {{{set-read-syntax!}}}, {{{set-parameterized-read-syntax!}}}
 and {{{set-sharp-read-syntax!}}}, which take 2 arguments (p restart)
 instead of just (p).  Invoking (restart) will restart the reader, like if
 you had returned zero values in the previous patch.  E.g.

 ;; instead of
 (set-read-syntax! #\! (lambda (p) (read-line p) (values)))

 ;; we can use
 (set-read-syntax!* #\! (lambda (p restart) (read-line p) (restart)))

 ;; then
 (list 'foo ! 'bar 'baz
 ; => (foo quux)


 The starred names are ugly, I also thought of {{{set-restartable-read-
 syntax!}}}, {{{set-restartable-sharp-read-syntax!}}} and {{{set-
 restartable-parameterizable-read-syntax!}}} but it gets ridiculously long.
 (To be fair, I doubt parameterizable read syntax will need a restartable

 Only thing this doesn't do is allow calls to {{{##sys#user-read-hook to
 restart}}}, but I can live with that!

Ticket URL: <>
Chicken Scheme <>
Chicken Scheme is a compiler for the Scheme programming language.

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