gen_bind: Compose dependent, sized, and recursive generators

In s7contract: Behavioral Contracts and Generative Laws for 'S7'

Compose dependent, sized, and recursive generators

Description

gen_bind() passes a generated value to bind, which constructs the next generator. Shrinking first rebuilds that generator for smaller source values, then shrinks its output. Each rebuild uses the same locally captured seed and size, so random downstream draws remain reproducible regardless of shrink traversal or random draws made by a law. The surrounding RNG state is restored after each rebuild. Callbacks must not depend on external mutable state or change the RNG configuration.

Usage

gen_bind(generator, bind, prototype = list())

gen_sized(factory, prototype = list())

gen_resize(generator, size)

gen_recursive(base, expand, prototype = list())

Arguments

generator, base	A generator. base produces non-recursive values.
bind	Function of one generated value returning a generator.
prototype	Zero-length prototype of generated values, used when this generator is an element of gen_vector(). Defaults to list elements.
factory	Function of one non-negative integer size returning a generator.
size	Non-negative integer size to use for every draw.
expand	Function accepting a child generator and returning a generator for one recursive layer.

Details

gen_sized() passes the current size to a generator factory. gen_resize() fixes the size used by one generator without changing its siblings.

gen_recursive() chooses between base and the generator returned by expand(child). The supplied child recursively uses half the current size, rounded down; size zero draws only from base. Shrinking tries the base branch before shrinking the expanded value. Recursion through child therefore terminates, provided callbacks themselves terminate and do not introduce other recursion. Size bounds recursion depth, not total node count.

Value

An S7 generator object.

Examples

sized_vectors <- gen_bind(gen_integer(1L, 8L), function(n) {
  gen_product(n = gen_constant(n), x = gen_vector(gen_integer(), n, n))
})
gen_example(sized_vectors)

trees <- gen_recursive(gen_constant(0L), function(child) {
  gen_product(left = child, right = child)
})
gen_example(trees, size = 4L)

s7contract documentation built on Sept. 10, 2026, 1:09 a.m.