maybe.h File Reference

An optional value. More...

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Macros
#define	ML99_just(x)
	Some value x.
#define	ML99_nothing(...)
	No value.
#define	ML99_isJust(maybe)
	ML99_true() if maybe contains some value, otherwise ML99_false().
#define	ML99_isNothing(maybe)
	The inverse of ML99_isJust.
#define	ML99_maybeEq(cmp, maybe, other)
	Tests maybe and other for equality.
#define	ML99_maybeUnwrap(maybe)
	Returns the contained value on ML99_just(x) or emits a fatal error on ML99_nothing().
#define	ML99_JUST(x)
#define	ML99_NOTHING(...)
#define	ML99_IS_JUST(maybe)
#define	ML99_IS_NOTHING(maybe)

Detailed Description

An optional value.

Macro Definition Documentation

ML99_IS_JUST

#define ML99_IS_JUST

(

maybe

)

Value:

ML99_PRIV_IS_JUST(maybe)

ML99_IS_NOTHING

#define ML99_IS_NOTHING

(

maybe

)

Value:

ML99_NOT(ML99_IS_JUST(maybe))

ML99_isJust

#define ML99_isJust

(

maybe

)

Value:

ML99_call(ML99_isJust, maybe)

ML99_true() if maybe contains some value, otherwise ML99_false().

Examples

#include <metalang99/maybe.h>
 
// 1
ML99_isJust(ML99_just(v(123)))
 
// 0
ML99_isJust(ML99_nothing())

ML99_isNothing

#define ML99_isNothing

(

maybe

)

Value:

ML99_call(ML99_isNothing, maybe)

The inverse of ML99_isJust.

Examples

#include <metalang99/maybe.h>
 
// 1
ML99_isNothing(ML99_nothing())
 
// 0
ML99_isNothing(ML99_just(v(123)))

ML99_JUST

#define ML99_JUST

(

x

)

Value:

ML99_CHOICE(just, x)

ML99_just

#define ML99_just

(

x

)

Value:

ML99_call(ML99_just, x)

Some value x.

ML99_maybeEq

#define ML99_maybeEq	(		cmp,
			maybe,
			other )

Value:

ML99_call(ML99_maybeEq, cmp, maybe, other)

Tests maybe and other for equality.

Examples

#include <metalang99/maybe.h>
#include <metalang99/nat.h>
 
// 1
ML99_maybeEq(v(ML99_natEq), ML99_just(v(123)), ML99_just(v(123)));
 
// 0
ML99_maybeEq(v(ML99_natEq), ML99_just(v(4)), ML99_just(v(6)));
 
// 0
ML99_maybeEq(v(ML99_natEq), ML99_just(v(4)), ML99_nothing());

ML99_maybeUnwrap

#define ML99_maybeUnwrap

(

maybe

)

Value:

ML99_call(ML99_maybeUnwrap, maybe)

Returns the contained value on ML99_just(x) or emits a fatal error on ML99_nothing().

Examples

#include <metalang99/maybe.h>
 
// 123
ML99_maybeUnwrap(ML99_just(v(123)))
 
// Emits a fatal error.
ML99_maybeUnwrap(ML99_nothing())

ML99_NOTHING

#define ML99_NOTHING

(

...

)

Value:

ML99_CHOICE(nothing, ~)

ML99_nothing

#define ML99_nothing

(

...

)

Value:

ML99_callUneval(ML99_nothing, )

No value.