Control structures

Case

A case expression has the following syntax:

case value
| pat1 := branch1
..
| patN := branchN

For example, one can evaluate the following expression in the REPL:

Stdlib.Prelude> case 2 | zero := 0 | suc x := x | _ := 19
1

Lazy builtins

The standard library provides several builtin functions which are treated specially and evaluated lazily. These builtins must always be fully applied.

• if condition branch1 branch2. First evaluates condition, if true evaluates and returns branch1, otherwise evaluates and returns branch2.
• a || b. Lazy disjunction. First evaluates a, if true returns true, otherwise evaluates and returns b.
• a && b. Lazy conjunction. First evaluates a, if false returns false, otherwise evaluates and returns b.
• a >> b. Sequences two IO actions. Lazy in the second argument.