11 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 Each thread has its own initial parameterization, which is extended functionally and superseded by parameterizations that are attached to a particular continuation mark.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_CAN_READ_DOT — read-accept-dot
MZCONFIG_CAN_READ_INFIX_DOT — read-accept-infix-dot
MZCONFIG_CAN_READ_QUASI — read-accept-quasiquote
MZCONFIG_CAN_READ_READER — read-accept-reader
MZCONFIG_CAN_READ_LANG — read-accept-lang
MZCONFIG_READ_DECIMAL_INEXACT — read-decimal-as-inexact
MZCONFIG_READ_CDOT — read-cdot
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_SQUARE_BRACKETS_ARE_TAGGED — read-square-brackets-with-tag
MZCONFIG_CURLY_BRACES_ARE_TAGGED — read-curly-braces-with-tag
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 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.

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1	Overview
2	Embedding into a Program
3	Writing Racket Extensions
4	Values and Types
5	Memory Allocation
6	Namespaces and Modules
7	Procedures
8	Evaluation
9	Exceptions and Escape Continuations
10	Threads
11	Parameterizations
12	Continuation Marks
13	String Encodings
14	Bignums, Rationals, and Complex Numbers
15	Ports and the Filesystem
16	Structures
17	Security Guards
18	Custodians
19	Subprocesses
20	Miscellaneous Utilities
	Index