Boolean

Common commands that can be used with bool

• if, while

• match (in clauses where the expression matches the clause expression, or the _ value which is always true)

• is-empty, is-not-empty

• is-admin

• is-terminal

The following commands take a closure (or a row condition) as their main argument. The return value from the closure must be a boolean:

• where
• any, all, skip until, skip while, take until, take while

Common operators that can be used with bool

• ==, !=, <, <=, >, >=
• and, or, xor, not
• in
• Regex comparison operators: =~, !~ <regex>
• String comparison operators: ends-with, starts-with

Short-circuit evaluation

and and or short-circuit: the right-hand operand is only evaluated when the left-hand operand doesn't already decide the result. With and, the right-hand side is skipped when the left-hand side is false; with or, it is skipped when the left-hand side is true.

def check [] { print "check was called"; true }

false and (check)
# => false

true or (check)
# => true

true and (check)
# => check was called
# => true

This means a condition can guard an expression that would otherwise fail:

let text = ""
($text != "") and (($text | split chars | last) == "%")
# => false