[Chicken-janitors] #516: letrec fails when used in re-assigning top-level bindings

[Chicken Trac]

#516: letrec fails when used in re-assigning top-level bindings
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 Reporter:  syn                        |       Owner:  felix
     Type:  defect                     |      Status:  new  
 Priority:  major                      |   Milestone:  4.7.0
Component:  compiler                   |     Version:  4.6.x
 Keywords:  compiler letrec top-level  |  
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 The following program works as expected when interpreted, i.e. it prints
 "hey". However, when compiled it prints {{{#<unbound value>}}} or, when
 compiled as a shared object, it signals {{{unbound variable: foo#bar}}}.
 The comments in the program point out two ways of making it work when
 compiled. It seems that the optimizer removes the original binding of
 {{{bar}}} when {{{letrec}}} is used for its redefinition. Putting some
 top-level code between definition and re-definition prevents that as well
 as replacing {{{letrec}}} with {{{let*}}}. Note that the module form can
 be left out to reproduce the problem, too.

 {{{

 (module foo

 (bar)
 (import chicken scheme)

 (define bar 'hey)

 ;; uncommenting the next line makes it work when compiled
 ;; (print 'some-top-level-expression)

 (set! bar
       ;; changing the letrec to a let* also makes it work when compiled
       (letrec ((baz bar)
                (qux (lambda () baz)))
         qux))

 (print (bar))

 )

 }}}

-- 
Ticket URL: <http://bugs.call-cc.org/ticket/516>
Chicken Scheme <http://www.call-with-current-continuation.org/>
Chicken Scheme is a compiler for the Scheme programming language.