Standard Types

These types are predefined with the following names.

Instead if 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/Scheme.java.

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

Variable: Object

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

Variable: number

The type of Scheme numbers.

Variable: quantity

The type of quantities optionally with units. This is a sub-type of number.

Variable: complex

The type of complex numbers. This is a sub-type of quantity.

Variable: real

The type of real numbers. This is a sub-type of complex.

Variable: rational

The type of exact rationl numbers. This is a sub-type of real.

Variable: integer

The type of exact Scheme integers. This is a sub-type of rational.

Variable: symbol

The type of Scheme symbols. (Implemented using the Java class gnu.mapping.Symbol.) (Compatibility note: 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 note: Previous versions of Kawa implemented 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 methods any parameter whose type is java.lang.String is converted as if it was declared as a String.

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.