gen_double: Generate finite double values

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

Generate finite double values

Description

At size zero, gen_double() draws only origin. The bounds expand linearly from the origin to min and max, reaching the full interval at size 100. Larger sizes use that same interval. Use gen_resize() to sample the full range at every runner size. Within the current bounds, generation interpolates one uniform draw from stats::runif(). This samples a finite-precision approximation to a continuous uniform distribution, not all representable doubles uniformly. Bounds are inclusive constraints; endpoints are not guaranteed to be drawn. Use gen_choice() with constants to target them.

Usage

gen_double(min = -100, max = 100, origin = NULL)

Arguments

min, max	Finite scalar numeric bounds, with min <= max.
origin	Finite scalar numeric shrink target within the bounds. NULL chooses zero when it is in range, otherwise the nearest bound.

Details

Shrinking tries the origin, then the midpoint between the origin and the generated value, then successive midpoints approaching that value. For example, 8 with origin 0 has children 0, 4, 6, 7, 7.5, and so on. Each child follows the same rule. Candidates remain between the origin and their parent; iteration stops when rounding prevents further progress. Children are built only when visited. Values close to zero can require many steps to shrink through subnormal doubles, so the runner's evaluation budget still applies.

NA, NaN, and infinities are excluded. Add them explicitly with gen_choice() or gen_element(). Branch weights control generation and branch order controls shrinking; zero-weight branches are excluded from both.

Value

An S7 generator with a double element prototype.

References

Haskell Hedgehog separates shrink origins from size-dependent bounds and uses fractional shrinking toward an origin. The R Hedgehog manual documents gen.unif() and mixtures with exceptional numeric values.

Examples

measurements <- gen_double(-10, 10)
gen_example(measurements, size = 100L)

# 80% finite draws; 5% each for NA, NaN, -Inf, and Inf.
numeric_values <- gen_choice(
  measurements, gen_element(c(NA_real_, NaN, -Inf, Inf)),
  prob = c(4, 1)
)
gen_example(gen_vector(numeric_values, max = 5L))

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