* libguile/fluids.c (scm_make_undefined_fluid, scm_fluid_unset_x)
(scm_fluid_bound_p): New functions.
(fluid_ref): New function; like scm_fluid_ref, but will not throw an
error for unbound fluids.
(scm_fluid_ref, swap_fluid): Use `fluid_ref'.
* libguile/fluids.h (scm_make_undefined_fluid, scm_fluid_unset_x)
(scm_fluid_bound_p): New prototypes.
* libguile/vm-i-system.c (fluid_ref): If fluid is unbound, jump to
`vm_error_unbound_fluid'.
* libguile/vm-engine.c (VM_NAME)[vm_error_unbound_fluid]: New error
message.
* test-suite/tests/fluids.test ("unbound fluids")["fluid-ref of unbound
fluid", "fluid-bound? of bound fluid", "fluid-bound? of unbound
fluid", "unbound fluids can be set", "bound fluids can be unset"]: New
tests.
* module/ice-9/boot-9.scm:
* module/ice-9/deprecated.scm (@bind): Deprecate @bind, which was a
thread-unsafe dynamic scoping mechanism, used in the old elisp
support. Fluids are more correct, and are probably faster, given the
VM support for with-fluids.
* test-suite/tests/dynamic-scope.test: Remove.
* test-suite/tests/fluids.test: Move relevant tests from
dynamic-scope.test here, recast in terms of with-fluids.
* test-suite/tests/fluids.test ("initial fluid values")["initial value
is inherited from parent thread"]: New test.
("fluid values are thread-local"): New test.
* libguile/tags.h (scm_tc7_with_fluids): Allocate a tc7 for
"with-fluids" objects, which will only live on the dynamic stack (wind
list), not in normal scheme-land.
* libguile/fluids.h (SCM_WITH_FLUIDS_P, SCM_WITH_FLUIDS_LEN)
(SCM_WITH_FLUIDS_NTH_FLUID, SCM_WITH_FLUIDS_NTH_VAL)
(SCM_WITH_FLUIDS_SET_NTH_VAL): Add some accessors.
* libguile/fluids.c (scm_i_make_with_fluids, scm_i_swap_with_fluids):
New internal functions.
(scm_c_with_fluids, scm_c_with_fluid): Push with-fluids objects on the
dynwind list, not winders.
* libguile/dynwind.c (scm_i_dowinds): Add cases for winding and
unwinding with-fluids objects.
* libguile/memoize.h (scm_sym_with_fluids, SCM_M_BEGIN): New public
data.
* libguile/memoize.c (scm_m_with_fluids): Define with-fluids as a
primitive syntax.
(unmemoize): Add with-fluids case.
* libguile/eval.c (eval):
* module/ice-9/eval.scm (primitive-eval): Add with-fluids cases.
* test-suite/tests/fluids.test
("fluids not modified if nonfluid passed to with-fluids"): Enable a
now-passing test.
