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14.12.1 Textual Port Types

The procedures in this section provide means for constructing port types with standard and custom operations, and accessing their operations.

procedure: make-textual-port-type operations port-type

Creates and returns a new port type. Operations must be a list; each element is a list of two elements, the name of the operation (a symbol) and the procedure that implements it. Port-type is either #f or a port type; if it is a port type, any operations implemented by port-type but not specified in operations will be implemented by the resulting port type.

Operations need not contain definitions for all of the standard operations; the procedure will provide defaults for any standard operations that are not defined. At a minimum, the following operations must be defined: for input ports, read-char and peek-char; for output ports, either write-char or write-substring. I/O ports must supply the minimum operations for both input and output.

If an operation in operations is defined to be #f, then the corresponding operation in port-type is not inherited.

If read-char is defined in operations, then any standard input operations defined in port-type are ignored. Likewise, if write-char or write-substring is defined in operations, then any standard output operations defined in port-type are ignored. This feature allows overriding the standard operations without having to enumerate them.

procedure: textual-port-type? object
procedure: textual-input-port-type? object
procedure: textual-output-port-type? object
procedure: textual-i/o-port-type? object

These predicates return #t if object is a port type, input-port type, output-port type, or I/O-port type, respectively. Otherwise, they return #f.

obsolete procedure: make-port-type operations port-type
obsolete procedure: port-type? object
obsolete procedure: input-port-type? object
obsolete procedure: output-port-type? object
obsolete procedure: i/o-port-type? object

These procedures are deprecated; use the procedures defined above.

obsolete procedure: port-type/operations port-type
obsolete procedure: port-type/operation-names port-type
obsolete procedure: port-type/operation port-type symbol

These procedures are deprecated and will be removed in the near future. There are no replacements planned.

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