4288c6c2c7
punctuations outside of the form, as it does with quote punctuations.
So things like this
#, @foo{...}
that required the space to make the @foo read as a scribble form are
now better written as
@#,foo{...}
This changes all such occurrences. (In case you see this change in
your files and are worried that there might be changes: I mechanically
verified that the result of `read'ing the modified files is identical
to the previous version.)
svn: r15111
226 lines
7.0 KiB
Racket
226 lines
7.0 KiB
Racket
#lang scribble/doc
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@(require "mz.ss"
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(for-label scheme/control))
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@title{Classical Control Operators}
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@note-lib-only[scheme/control]
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The @scheme[scheme/control] library provides various control operators
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from the research literature on higher-order control operators, plus a
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few extra convenience forms. These control operators are implemented
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in terms of @scheme[call-with-continuation-prompt],
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@scheme[call-with-composable-continuations], etc., and they generally
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work sensibly together. Many are redundant; for example,
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@scheme[reset] and @scheme[shift] are aliases.
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@; ----------------------------------------------------------------------
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@defproc[(abort [v any/c] ...) any]{
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Returns the @scheme[v]s to a prompt using the default continuation
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prompt tag and the default abort handler.
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That is, @scheme[(abort v ...)] is equivalent to
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@schemeblock[
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(abort-current-continuation
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(default-continuation-prompt-tag)
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(lambda () (values v ...)))
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]}
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@; ----------------------------------------------------------------------
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@deftogether[(
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@defform*[[(% expr)
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(% expr handler-expr)]]
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@defproc[(fcontrol [v any/c]) any]
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)]{
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Sitaram's operators @cite["Sitaram93"].
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The essential reduction rules are:
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@schemeblock[
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(% _val proc) => _val
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(% _E[(fcontrol _val)] _proc) => (_proc _val (lambda (_x) _E[_x]))
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(code:comment @#,t{where @scheme[_E] has no @scheme[%]})
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]
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When @scheme[handler-expr] is omitted, @scheme[%] is the same as
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@scheme[prompt].}
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@; ----------------------------------------------------------------------
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@deftogether[(
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@defform[(prompt expr ...+)]
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@defform[(control id expr ...+)]
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)]{
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Among the earliest operators for higher-order control
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@cite["Felleisen88" "Sitaram90"].
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The essential reduction rules are:
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@schemeblock[
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(prompt _val) => _val
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(prompt _E[(control _k _expr)]) => (prompt ((lambda (_k) _expr)
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(lambda (_v) _E[_v])))
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(code:comment @#,t{where @scheme[_E] has no @scheme[prompt]})
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]}
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@; ----------------------------------------------------------------------
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@deftogether[(
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@defform[(prompt-at prompt-tag-expr expr ...+)]
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@defform[(control-at prompt-tag-expr id expr ...+)]
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)]{
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Like @scheme[prompt] and @scheme[control], but using specific prompt
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tags:
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@schemeblock[
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(prompt-at _tag _val) => _val
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(prompt-at _tag _E[(control-at _tag _k _expr)]) => (prompt-at _tag
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((lambda (_k) _expr)
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(lambda (_v) _E[_v])))
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(code:comment @#,t{where @scheme[_E] has no @scheme[prompt-at] for @scheme[_tag]})
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]}
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@; ----------------------------------------------------------------------
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@deftogether[(
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@defform[(reset expr ...+)]
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@defform[(shift id expr ...+)]
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)]{
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Danvy and Filinski's operators @cite["Danvy90"].
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The essential reduction rules are:
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@schemeblock[
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(reset _val) => _val
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(reset _E[(shift _k _expr)]) => (reset ((lambda (_k) _expr)
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(lambda (_v) (reset _E[_v]))))
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(code:comment @#,t{where @scheme[_E] has no @scheme[reset]})
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]
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The @scheme[reset] and @scheme[prompt] forms are interchangeable.}
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@; ----------------------------------------------------------------------
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@deftogether[(
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@defform[(reset-at prompt-tag-expr expr ...+)]
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@defform[(shift-at prompt-tag-expr identifer expr ...+)]
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)]{
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Like @scheme[reset] and @scheme[shift], but using the specified prompt
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tags.}
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@; ----------------------------------------------------------------------
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@deftogether[(
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@defform[(prompt0 expr ...+)]
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@defform[(reset0 expr ...+)]
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@defform[(control0 id expr ...+)]
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@defform[(shift0 id expr ...+)]
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)]{
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Generalizations of @scheme[prompt], etc. @cite["Shan04"].
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The essential reduction rules are:
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@schemeblock[
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(prompt0 _val) => _val
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(prompt0 _E[(control0 _k _expr)]) => ((lambda (_k) _expr)
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(lambda (_v) _E[_v]))
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(reset0 _val) => _val
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(reset0 _E[(shift0 _k _expr)]) => ((lambda (_k) _expr)
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(lambda (_v) (reset0 _E[_v])))
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]
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The @scheme[reset0] and @scheme[prompt0] forms are interchangable.
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Furthermore, the following reductions apply:
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@schemeblock[
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(prompt _E[(control0 _k _expr)]) => (prompt ((lambda (_k) _expr)
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(lambda (_v) _E[_v])))
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(reset _E[(shift0 _k _expr)]) => (reset ((lambda (_k) _expr)
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(lambda (_v) (reset0 _E[_v]))))
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(prompt0 _E[(control _k _expr)]) => (prompt0 ((lambda (_k) expr)
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(lambda (_v) _E[_v])))
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(reset0 _E[(shift _k _expr)]) => (reset0 ((lambda (_k) expr)
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(lambda (_v) (reset _E[_v]))))
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]
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That is, both the @scheme[prompt]/@scheme[reset] and
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@scheme[control]/@scheme[shift] sites must agree for @scheme[0]-like
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behavior, otherwise the non-@scheme[0] behavior applies.}
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@; ----------------------------------------------------------------------
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@deftogether[(
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@defform[(prompt0-at prompt-tag-expr expr ...+)]
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@defform[(reset0-at prompt-tag-expr expr ...+)]
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@defform[(control0-at prompt-tag-expr id expr ...+)]
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@defform[(shift0-at prompt-tag-expr id expr ...+)]
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)]{
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Variants of @scheme[prompt0], @|etc| that accept a prompt tag.}
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@; ----------------------------------------------------------------------
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@defproc[(spawn [proc ((any/c . -> . any) . -> . any)]) any]{
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The operators of Hieb and Dybvig @cite["Hieb90"].
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The essential reduction rules are:
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@schemeblock[
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(prompt-at _tag _obj) => _obj
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(spawn _proc) => (prompt _tag (_proc (lambda (_x) (abort _tag _x))))
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(prompt-at _tag _E[(abort _tag _proc)])
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=> (_proc (lambda (_x) (prompt-at _tag _E[_x])))
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(code:comment @#,t{where @scheme[_E] has no @scheme[prompt-at] for @scheme[_tag]})
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]}
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@; ----------------------------------------------------------------------
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@defproc[(splitter [proc (((-> any) . -> . any)
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((continuation? . -> . any) . -> . any)
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. -> . any)])
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any]{
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The operator of Queinnec and Serpette @cite["Queinnec91"].
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The essential reduction rules are:
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@schemeblock[
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(splitter _proc) => (prompt-at _tag
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(_proc (lambda (_thunk)
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(abort _tag _thunk))
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(lambda (_proc)
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(control0-at _tag _k (_proc _k)))))
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(prompt-at _tag _E[(abort _tag _thunk)]) => (_thunk)
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(code:comment @#,t{where @scheme[_E] has no @scheme[prompt-at] for @scheme[_tag]})
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(prompt-at _tag _E[(control0-at _tag _k _expr)]) => ((lambda (_k) _expr)
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(lambda (_x) _E[_x]))
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(code:comment @#,t{where @scheme[_E] has no @scheme[prompt-at] for @scheme[_tag]})
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]}
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@; ----------------------------------------------------------------------
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@deftogether[(
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@defproc[(new-prompt) any]
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@defform[(set prompt-expr expr ...+)]
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@defform[(cupto prompt-expr id expr ...+)]
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)]{
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The operators of Gunter et al. @cite["Gunter95"].
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In this library, @scheme[new-prompt] is an alias for
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@scheme[make-continuation-prompt-tag], @scheme[set] is an alias for
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@scheme[prompt0-at], and @scheme[cupto] is an alias for @scheme[control0-at].
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}
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