Data Types and Predicates


Data Types and Predicates
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— testing for data types.

Unlike many languages, just about every expression in Gamma is a data type. This gives the flexibility to manipulate functions, arrays, lists, classes, instances and so on as if they were data.

The following data types are defined in Gamma. Beside each data type is the name of a function which can be used to test an expression for that type. These functions are called predicates, and will return t if the test is true (the expression is that data type), or nil if it is false.

Table 3. Data Types and Related Predicates

Type	Predicate	Comments
alist	`alist_p`	An association list. See `assoc`.
array	`array_p`	See `array` and Lists and Arrays.
autotrace	`autotrace_p`
breakpoint	`breakpoint_p`
buffer	`buffer_p`	See `buffer`.
builtin	`builtin_p`
class	`class_p`	See `class`.
cons	`cons_p`	See `cons` and `list`.
constant	`constant_p`	Constants can be assigned or defined. See `defvar` and `::=`.
destroyed instance	`destroyed_p`	See `new` `(instance)`.
file	`file_p`	See `open` and `open_string`.
fixed-point real	`fixed_point_p`	See Numeric Types.
function	`function_p`	See `function`.
instance	`instance_p`	See `new` `(instance)`.
integer	`int_p`, `long_p`	See Literals.
list	`list_p`	See `list` and Lists and Arrays.
macro	`macro_p`	See `macro`.
method	`method_p` (obsolete, always returns `nil`)	See `method`.
nil	`nil_p`	See `nil`.
number	`number_p`	Integer and floating point values are both considered numbers. See Literals.
real	`real_p`	See Literals.
registered	`registered_p`	See `register_point`.
string	`string_p`	See Literals and `string`.
sym-alist	`sym_alist_p`	A symbol-indexed association list. See `assoc`.
symbol	`symbol_p`	See Literals.
t	`true_p`	See t.
task descriptor	none	See `locate_task`.
undefined	`undefined_p`	See `undefined_p`.
undefined symbol	`undefined_symbol_p`	See `undefined_symbol_p`.

Predicates

Predicates are used to test a Gamma object for a given type, as listed. If a Gamma object is of that type, the predicate will return the value t.

Syntax

alist_p (s_exp)
array_p (s_exp)
autotrace_p (s_exp)
breakpoint_p (s_exp)
buffer_p (s_exp)
builtin_p (s_exp)
class_p (s_exp)
cons_p (s_exp)
constant_p (s_exp)
destroyed_p (s_exp)
file_p (s_exp)
fixed_point_p (s_exp)
function_p (s_exp)
instance_p (s_exp)
int_p (s_exp)
list_p (s_exp)
long_p (s_exp)
macro_p (s_exp)
method_p (s_exp)
nil_p (s_exp)
number_p (s_exp)
real_p (s_exp)
registered_p (s_exp)
string_p (s_exp)
sym_alist_p (s_exp)
symbol_p (s_exp)
true_p (s_exp)
none_p (s_exp)
undefined_p (s_exp)
undefined_symbol_p (s_exp)

Arguments

any expression

Returns

t or nil.

Example

Here is an example for the predicate function_p. All the other predicates work in a similar way.

Gamma> function_p(div);
t
Gamma> function_p(strcmp);
t
Gamma> function_p(5);
nil
Gamma>