Control flow

Conditionals

Conditionals produce values:

Fragment:

if score >= 60 then "pass" else "retry"

The condition must be Bool, and both branches must have compatible types. Only the selected branch is evaluated.

Cases and guards

Cases try arms from top to bottom:

Fragment:

case input {
  | Just item -> item
  | Nothing -> 0
}

Failed patterns fall through without evaluating their guards. A matching arm's guard can use names bound by the pattern; False continues to the next arm. Guards must be Bool, and every arm body must produce a compatible result type. Ordered pattern lambdas use the same selection rules.

Cases and pattern lambdas must be statically exhaustive. Only unguarded arms contribute to coverage, so a guarded arm always needs an unguarded covering arm elsewhere. The compiler reports E2018 with a missing-pattern example when coverage is incomplete and E2019 when earlier unguarded arms make an entire later arm unreachable.

The runtime keeps E3022 as a defensive boundary for independently constructed canonical core. Source programs that pass compilation do not rely on it for ordinary match selection.

Static checks

Jazz has no imperative loop construct. Repetition uses recursion or collection operations such as the folds in the List module.