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18.1 Standard Types

These types are predefined with the following names.

Instead of plain typename you can also use the syntax <typename> with angle brackets, but that syntax is no longer recommended, because it doesn’t “fit” as well with some ways type names are used.

To find which Java classes these types map into, look in kawa/standard/

Note that the value of these variables are instances of gnu.bytecode.Type, not (as you might at first expect) java.lang.Class.

The numeric types (number, quantity, complex, real, rational, integer, long, int, short, byte ulong, uint, ushort, ubyte, double, float) are discussed in Numerical types.

The types character and char are discussed in Characters.

Variable: Object

An arbitrary Scheme value - and hence an arbitrary Java object.

Variable: symbol

The type of Scheme symbols. (Implemented using the Java class gnu.mapping.Symbol.) (Compatibility: Previous versions of Kawa implemented a simple Scheme symbol using an interned java.lang.String.)

Variable: keyword

The type of keyword values. See Keywords.

Variable: list

The type of Scheme lists (pure and impure, including the empty list).

Variable: pair

The type of Scheme pairs. This is a sub-type of list.

Variable: string

The type of Scheme strings. (Implemented using java.lang.String for immutable strings, and gnu.lists.FString for mutable strings. Both of these implement the interface java.lang.CharSequence. In the future, we may change the representation for strings containing “surrogate characters”, for efficient indexing.) (Compatibility: Previous versions of Kawa always used gnu.lists.FString.)

Variable: character

The type of Scheme character values. This is a sub-type of Object, in contrast to type char, which is the primitive Java char type.

Variable: vector

The type of Scheme vectors.

Variable: procedure

The type of Scheme procedures.

Variable: input-port

The type of Scheme input ports.

Variable: output-port

The type of Scheme output ports.

Variable: String

This type name is a special case. It specifies the class java.lang.String. However, coercing a value to String is done by invoking the toString method on the value to be coerced. Thus it "works" for all objects. It also works for #!null.

When Scheme code invokes a Java method, any parameter whose type is java.lang.String is converted as if it was declared as a String.

Variable: parameter

A parameter object, as created by make-parameter. This type can take a type parameter (sic):

(define-constant client ::parameter[Client] (make-parameter #!null))

This lets Kawa know that reading the parameter (as in (client)) returns a value of the specified type (in this case Client).

More will be added later.

A type specifier can also be one of the primitive Java types. The numeric types long, int, short, byte, float, and double are converted from the corresponding Scheme number classes. Similarly, char can be converted to and from Scheme characters. The type boolean matches any object, and the result is false if and only if the actual argument is #f. (The value #f is identical to Boolean.FALSE, and #t is identical to Boolean.TRUE.) The return type void indicates that no value is returned.

A type specifier can also be a fully-qualified Java class name (for example java.lang.StringBuffer). In that case, the actual argument is cast at run time to the named class. Also, java.lang.StringBuffer[] represents an array of references to java.lang.StringBuffer objects.

Variable: dynamic

Used to specify that the type is unknown, and is likely to change at run-time. Warnings about unknown member names are supressed (a run-time name lookup is formed). An expression of type dynamic is (statically) compatible with any type.

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