none-coalescing operator

The none-coalescing operator (??) selects a fallback only when its left operand evaluates to none.

example.fql

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let user = { profile: {} } return user?.profile?.displayName ?? "Anonymous"

If displayName is missing, optional chaining produces none and the expression returns "Anonymous".

How it evaluates

For left ?? right, FQL evaluates left once.

If left is not none, the expression returns it without evaluating right.
If left is none, FQL evaluates and returns right.

The two operands may have different types. The selected operand becomes the result without conversion.

Only none selects the fallback

null represents the same absent runtime value as none, so both select the fallback. Other values remain present even when a logical operator would treat them as false.

Left operand	Result of `left ?? "fallback"`
`none`	`"fallback"`
`null`	`"fallback"`
`false`	`false`
`0`	`0`
`""`	`""`
`[]`	`[]`
`{}`	`{}`

This makes ?? useful when false, zero, or an empty value carries meaning and must not be replaced.

Coalescing and logical or

Logical or selects its right operand when the left operand is false according to FQL’s truth-value rules. ?? selects its right operand only for none.

Value	`value or "fallback"`	`value ?? "fallback"`
`none`	`"fallback"`	`"fallback"`
`false`	`"fallback"`	`false`
`0`	`"fallback"`	`0`
`""`	`"fallback"`	`""`

Use or for truth-based control flow. Use ?? for an absent-value fallback.

Short-circuiting and errors

The fallback expression is evaluated only when the left operand is none.

example.fql

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func buildDefaultName() => "Anonymous" let name = "Ada" // The fallback function is not called. return name ?? buildDefaultName()

?? does not catch runtime errors. An error from the left operand propagates before FQL can test the value:

example.fql

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// Division by zero still fails. return (1 / 0) ?? 42

Apply recovery first when an error should become none and then select a fallback:

example.fql

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// Postfix recovery turns the error into NONE, so this returns 42. return (1 / 0)? ?? 42

See Error Handling for explicit recovery options.

Associativity and precedence

?? is right-associative. A chain groups from the right:

example.fql

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let primary = none let secondary = none return { chain: primary ?? secondary ?? "fallback", grouped: primary ?? (secondary ?? "fallback") }

Logical or binds more tightly than ??, while ?? binds more tightly than the ternary operator. Parentheses can make a different grouping explicit.

See Operator Precedence for the complete order.

Next steps

Learn Operators Compare, combine, and transform values with FQL's operators. Learn Logical Operators Logical and, or, not operators with short-circuit evaluation and boolean conversion. Learn Ternary Operator Conditional evaluation with the ternary operator and its shortcut form. Learn Error Handling Recover from runtime failures with recovery tails and optional chaining.