18 Parameterizations (BC)
A parameterization is a set of parameter values. Each thread
has its own initial parameterization, which is extended functionally
and superseded by parameterizations that are attached to a particular
continuation mark.
Parameterization information is stored in a Scheme_Config
record. For the currently executing thread,
scheme_current_config returns the current parameterization.
To obtain parameter values, a Scheme_Config is combined with the
current threads Scheme_Thread_Cell_Table, as stored in the
thread record’s cell_values field.
Parameter values for built-in parameters are obtained and modified
(for the current thread) using scheme_get_param and
scheme_set_param. Each parameter is stored as a
Scheme_Object * value, and the built-in parameters are accessed
through the following indices:
To get or set a parameter value for a thread other than the current
one, use scheme_get_thread_param and
scheme_set_thread_param, each of which takes a
Scheme_Thread_Cell_Table to use in resolving or setting a
parameter value.
When installing a new parameter with scheme_set_param, no check
is performed on the supplied value to ensure that it is a legal value
for the parameter; this is the responsibility of the caller of
scheme_set_param. Note that Boolean parameters should only be
set to the values #t and #f.
New primitive parameter indices are created with
scheme_new_param and implemented with
scheme_make_parameter and scheme_param_config.
Gets the current value (for the current thread) of the parameter
specified by param_id.
Scheme_Object* | | scheme_set_param | ( | Scheme_Config* config, | | | | | int param_id, | | | | | Scheme_Object* v) |
|
Sets the current value (for the current thread) of the parameter
specified by param_id.
Scheme_Object* | scheme_set_thread_param | ( | Scheme_Config* config, | | | Scheme_Thread_Cell_Table* cells, | | | int param_id, | | | Scheme_Object* v) |
|
Creates and returns a parameterization that extends
base with a
new value
v (in all threads) for the parameter
param_id. Use
scheme_install_config to make this
configuration active in the current thread.
Adjusts the current thread’s continuation marks to make
config
the current parameterization. Typically, this function is called
after
scheme_push_continuation_frame to establish a new
continuation frame, and then
scheme_pop_continuation_frame
is called later to remove the frame (and thus the parameterization).
Creates a new thread-cell-value table, copying values for preserved
thread cells from cells.
Allocates a new primitive parameter index. This function must be
called
before scheme_basic_env, so it is only
available to embedding applications (i.e., not extensions).
Use this function instead of the other primitive-constructing
functions, like
scheme_make_prim, to create a primitive
parameter procedure. See also
scheme_param_config, below.
This function is only available to embedding applications (i.e., not
extensions).
Scheme_Object* | | scheme_param_config | ( | char* name, | | | | | Scheme_Object* param, | | | | | int argc, | | | | | Scheme_Object** argv, | | | | | int arity, | | | | | Scheme_Prim* check, | | | | | char* expected, | | | | | int isbool) |
|
Call this procedure in a primitive parameter procedure to implement
the work of getting or setting the parameter. The
name argument
should be the parameter procedure name; it is used to report
errors. The
param argument is a fixnum corresponding to the
primitive parameter index returned by
scheme_new_param. The
argc and
argv arguments should be the un-touched and
un-tested arguments that were passed to the primitive parameter.
Argument-checking is performed within
scheme_param_config
using
arity,
check,
expected, and
isbool:
If arity is non-negative, potential parameter values must
be able to accept the specified number of arguments. The check
and expected arguments should be NULL.
If check is not NULL, it is called to check a
potential parameter value. The arguments passed to check are
always 1 and an array that contains the potential parameter
value. If isbool is 0 and check returns
scheme_false, then a type error is reported using name
and expected as a type description. If isbool is 1, then a type error is
reported only when check returns NULL and any
non-NULL return value is used as the actual value to be stored
for the parameter.
Otherwise, isbool should be 1. A potential procedure
argument is then treated as a Boolean value.
This function is only available to embedding applications (i.e., not
extensions).
Scheme_Object* | | scheme_param_config2 | ( | char* name, | | | | | Scheme_Object* param, | | | | | int argc, | | | | | Scheme_Object** argv, | | | | | int arity, | | | | | Scheme_Prim* check, | | | | | char* expected_contract, | | | | | int isbool) |
|
The same as
scheme_param_config, but with
expected_contract as a contract instead of type description.