compile/assert

Symbol: compile/assert (surface: assert)

Syntax:

• (assert EXPR) – raise AssertionError when EXPR is falsey.

• (assert EXPR MESSAGE) – the same, with MESSAGE as the exception argument.

Behaviour: Expands to a falsey-check that raises AssertionError – effectively (unless EXPR (raise (AssertionError MESSAGE?))). MESSAGE is an ordinary expression and is evaluated only when the assertion fails.

The expansion is gated by the compiler/enable-asserts pragma setting (default on). When disabled, an assert form expands to nothing at all: neither the condition nor the message is compiled or evaluated, mirroring Python’s -O behavior. The gate is consulted as each assert form is compiled, so a pragma change is forward-only – it affects the asserts that appear after it, and an assert already compiled away stays gone even if asserts are re-enabled later in the load.

(assert (< x limit))
(assert (< x limit) f"x too large: {x}")

(pragma [compiler/enable-asserts False])
(assert (expensive-invariant-check))   ; compiles away entirely

See Pragmas and feature settings for how pragma forms work.