lambda_calculus is a simple implementation of the untyped lambda calculus in Rust.

§Stack depth

Reduction, and every other operation on a Term, walks a tree of boxes recursively, so stack use scales with how deeply nested the term is. Deep enough and the process dies on a guard page — a SIGSEGV with no unwinding, no panic message and no failing assertion.

Two unrelated things cause that, and only one of them is cured by a bigger stack.

An unbounded reduction is not: an applicative-family order (APP, HAP) applied to a term built on a recursion combinator never converges, so it exhausts whatever stack it is given. The functions this affects say so under # Errors; the answer is a normal-order strategy, not a larger stack_size.

A genuinely deep term is, because its depth is bounded by the input. That is worth measuring rather than guessing, and it can be measured without instrumenting anything — see the Stack depth section of the README for how, and for the figures this crate’s own tests/stack_depth.rs pins down. The short version: nesting costs roughly half a kilobyte per level unoptimized for beta, Term::clone, Debug and Display, which makes ~3600 levels the ceiling on the 2 MiB stack libtest gives each test. Debug is worth knowing about specifically because it is the path assert_eq! takes when it fails, so past its own limit a mismatch aborts while being rendered rather than reported.