9 Parameterizations

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 Each thread has its own initial parameterization, which is extended functionally and superseded by parameterizations that are attached to a particular continuation mark.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:

• MZCONFIG_ENV – current-namespace (use scheme_get_env)

• MZCONFIG_INPUT_PORT – current-input-port

• MZCONFIG_OUTPUT_PORT – current-output-port

• MZCONFIG_ERROR_PORT – current-error-port

• MZCONFIG_ERROR_DISPLAY_HANDLER – error-display-handler

• MZCONFIG_ERROR_PRINT_VALUE_HANDLER – error-value->string-handler

• MZCONFIG_EXIT_HANDLER – exit-handler

• MZCONFIG_INIT_EXN_HANDLER – uncaught-exception-handler

• MZCONFIG_EVAL_HANDLER – current-eval

• MZCONFIG_LOAD_HANDLER – current-load

• MZCONFIG_PRINT_HANDLER – current-print

• MZCONFIG_PROMPT_READ_HANDLER – current-prompt-read

• MZCONFIG_CAN_READ_GRAPH – read-accept-graph

• MZCONFIG_CAN_READ_COMPILED – read-accept-compiled

• MZCONFIG_CAN_READ_BOX – read-accept-box

• MZCONFIG_CAN_READ_PIPE_QUOTE – read-accept-bar-quote

• MZCONFIG_PRINT_GRAPH – print-graph

• MZCONFIG_PRINT_STRUCT – print-struct

• MZCONFIG_PRINT_BOX – print-box

• MZCONFIG_CASE_SENS – read-case-sensitive

• MZCONFIG_SQUARE_BRACKETS_ARE_PARENS – read-square-brackets-as-parens

• MZCONFIG_CURLY_BRACES_ARE_PARENS – read-curly-braces-as-parens

• MZCONFIG_ERROR_PRINT_WIDTH – error-print-width

• MZCONFIG_ALLOW_SET_UNDEFINED – allow-compile-set!-undefined

• MZCONFIG_CUSTODIAN – current-custodian

• MZCONFIG_USE_COMPILED_KIND – use-compiled-file-paths

• MZCONFIG_LOAD_DIRECTORY – current-load-relative-directory

• MZCONFIG_COLLECTION_PATHS – current-library-collection-paths

• MZCONFIG_PORT_PRINT_HANDLER – global-port-print-handler

• MZCONFIG_LOAD_EXTENSION_HANDLER – current-load-extension

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.

Scheme_Object*   scheme_get_param ( Scheme_Config* config,         int param_id)

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_get_thread_param ( Scheme_Config* config,     Scheme_Thread_Cell_Table* cells,     int param_id)

Like scheme_get_param, but using an arbitrary thread’s cell-value table.

Scheme_Object* scheme_set_thread_param ( Scheme_Config* config,     Scheme_Thread_Cell_Table* cells,     int param_id,     Scheme_Object* v)

Like scheme_set_param, but using an arbitrary thread’s cell-value table.

Scheme_Object*   scheme_extend_config ( Scheme_Config* base,         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.

void   scheme_install_config ( Scheme_Config* config)

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).

Scheme_Thread_Cell_Table* scheme_inherit_cells ( Scheme_Thread_Cell_Table* cells)

Creates a new thread-cell-value table, copying values for preserved thread cells from cells.

int   scheme_new_param ( )

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).

Scheme_Object*   scheme_register_parameter ( Scheme_Prim* function,         char* name,         int exnid)

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. 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).