maybe.h¶

An optional value.

Defines

ML99_just(x)¶: Some value x.

ML99_nothing(...)¶: No value.

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(maybe)¶

The inverse of ML99_isJust.

Examples

#include <metalang99/maybe.h>

// 1
ML99_isNothing(ML99_nothing())

// 0
ML99_isNothing(ML99_just(v(123)))

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(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_JUST(x)¶

ML99_NOTHING(...)¶

ML99_IS_JUST(maybe)¶

ML99_IS_NOTHING(maybe)¶