E0004: invalid use of !

Generated from rellum-diagnostics/src/db.rs.

Explanation

The ! character is part of effect identifiers such as print!, or the != operator. A standalone ! is not a unary operator in Rellum syntax.

Common causes

• writing !flag instead of the Rellum logical not form
• placing ! after punctuation instead of as part of an effect name
• starting an effect call without an identifier before !

Canonical fixes

• use not for logical negation

Before:

value = !flag

After:

value = not flag

• write a complete effect identifier

Before:

main! = !(value)

After:

main! = print!(value)

Code example

value = !flag

Links

• RellC diagnostic overview