A value of type 'a gen is a generator of values of type 'a.

A generator is a function of type unit -> 'a.

A generator has the ability to draw random data from a source that is specified (on the command line) when the Monolith engine is started. An end user who wishes to implement generator does not have direct access to this source of random data, but can access it indirectly by calling other generators such as bool, byte, bits, and so on.

A generator can fail if (somehow) it detects that it has made incorrect choices and entered a dead end. It does so by invoking the functions reject or guard. This not a fatal failure. This is a silent failure that causes the engine to backtrack (to an unspecified point) and retry.

Invoking a generator is permitted only while the engine is running, that is, while a call to main is ongoing.

reject generates nothing. It always fails.

guard b fails if b is false.

byte generates a byte. A byte is viewed as an unsigned integer. It is therefore a value in the semi-open interval [0, 256).

bits generates a signed integer.

bool generates a Boolean value.

char generates a character.

int n generates an integer in the semi-open interval [0, n). If this interval is empty, the generator fails.

semi_open_interval i j generates an integer in the semi-open interval [i, j). If this interval is empty, the generator fails.

closed_interval i j generates an integer in the closed interval [i, j]. If this interval is empty, the generator fails.

lt j is synonymous with int j and with semi_open_interval 0 j.

le j is synonymous with closed_interval 0 j.

sequential() produces a fresh stateful sequential generator of integers. This generator is deterministic. Every time this generator is invoked, it produces a new integer, counting from 0 and up.

choose xs picks an element in the list xs. If this list is empty, the generator fails.

An option generator.

A result generator.

A list generator. If n is a length generator (where a length is a nonnegative integer) and if element is an element generator then list n element is a list generator.

An array generator. If n is a length generator (where a length is a nonnegative integer) and if element is an element generator then array n element is a array generator.

A string generator. If n is a length generator (where a length is a nonnegative integer) and if char is a character generator then string n char is a string generator.