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(Fluids): Touched up a bit, added with-fluids.

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Marius Vollmer 2002-08-13 22:05:46 +00:00
parent dc61cbc6cd
commit a05a88b3b2
1 changed files with 24 additions and 16 deletions
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40
doc/ref/scheme-scheduling.texi
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@ -11,7 +11,7 @@ reviewed and largely reorganized.]
* Asyncs:: Asynchronous procedure invocation.
* Dynamic Roots:: Root frames of execution.
* Threads:: Multiple threads of execution.
* Fluids:: Dynamically scoped variables.
* Fluids:: Thread-local variables.
@end menu
@ -392,16 +392,17 @@ fluid are only visible in the same dynamic root. Since threads are
executed in separate dynamic roots, fluids can be used for thread local
storage (@pxref{Threads}).
Fluids can be used to simulate dynamically scoped variables. These are
used in several (especially in older) dialects of lisp, such as in Emacs
Lisp, and they work a bit like global variables in that they can be
modified by the caller of a procedure, and the called procedure will see
the changes. With lexically scoped variables---which are normally used
in Scheme---this cannot happen. See the description of
@code{with-fluids*} below for details.
Fluids can be used to simulate the desirable effects of dynamically
scoped variables. Dynamically scoped variables are useful when you
want to set a variable to a value during some dynamic extent in the
execution of your program and have them revert to their original value
when the control flow is outside of this dynamic extent. See the
description of @code{with-fluids} below for details.
New fluids are created with @code{make-fluid} and @code{fluid?} is used
for testing whether an object is actually a fluid.
New fluids are created with @code{make-fluid} and @code{fluid?} is
used for testing whether an object is actually a fluid. The values
stored in a fluid can be accessed with @code{fluid-ref} and
@code{fluid-set!}.
@deffn {Scheme Procedure} make-fluid
@deffnx {C Function} scm_make_fluid ()
@ -420,9 +421,6 @@ Return @code{#t} iff @var{obj} is a fluid; otherwise, return
@code{#f}.
@end deffn
The values stored in a fluid can be accessed with @code{fluid-ref} and
@code{fluid-set!}.
@deffn {Scheme Procedure} fluid-ref fluid
@deffnx {C Function} scm_fluid_ref (fluid)
Return the value associated with @var{fluid} in the current
@ -442,11 +440,21 @@ given values. After the procedure returns, the old values are restored.
@deffn {Scheme Procedure} with-fluids* fluids values thunk
@deffnx {C Function} scm_with_fluids (fluids, values, thunk)
Set @var{fluids} to @var{values} temporary, and call @var{thunk}.
@var{fluids} must be a list of fluids and @var{values} must be the same
number of their values to be applied. Each substitution is done
one after another. @var{thunk} must be a procedure with no argument.
@var{fluids} must be a list of fluids and @var{values} must be the
same number of their values to be applied. Each substitution is done
in the order given. @var{thunk} must be a procedure with no argument.
it is called inside a @code{dynamic-wind} and the fluids are
set/restored when control enter or leaves the established dynamic
extent.
@end deffn
@deffn {Scheme Macro} with-fluids ((fluid value) ...) body...
Execute @var{body...} while each @var{fluid} is set to the
corresponding @var{value}. Both @var{fluid} and @var{value} are
evaluated and @var{fluid} must yield a fluid. @var{body...} is
executed inside a @code{dynamic-wind} and the fluids are set/restored
when control enter or leaves the established dynamic extent.
@end deffn
@c Local Variables:
@c TeX-master: "guile.texi"