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has?

has? returns true if the given path expression is valid (regardless of the value it points to).

Examples

  • (set! $var 42) (has? $var.foo) ➜ false
  • (set! $var {foo "bar"}) (has? $var.foo) ➜ true

Forms

(has? expr:expression) ➜ bool

  • expr is exactly 1 expression. This can be any expression that supports path expressions (like variables, objects, vectors, tuples).

The value of the expression is evaluated without applying the path expression at first. If this evaluation results in an error, the error is returned from has?. If the value was successfully computed, the path expression is evaluated against it. The function then returns whether the path can be traversed successfully.

Context

has? evaluates the expression in its own scope, so variables defined in it do not leak.