No Boolean In Comparison

Explicit comparisons of expressions to boolean literals (true or false) should be avoided.

Avoid

mycondition(Assumptions) == true

mycondition(Assumptions) == false

mycondition(Assumptions) =/= true

mycondition(Assumptions) =:= false.

Prefer

mycondition(Assumptions)

not(mycondition(Assumptions))

not(mycondition(Assumptions))

not(mycondition(Assumptions)).

Rationale

Explicitly comparing expressions to boolean literals (e.g., Expr == true or Expr =/= false) is redundant and non-idiomatic in Erlang. Erlang's control flow constructs (such as if, case, guards, and boolean operators like andalso/orelse) are designed to evaluate the truthiness of expressions directly. Using direct comparisons can obscure intent, reduce readability, and increase the risk of subtle bugs - especially in cases where expressions yield non-boolean but truthy values (e.g., atoms or tuples). Favoring direct boolean evaluation leads to clearer, more idiomatic, and more maintainable code.

While developers might often use, for example, =:= (exactly equal to) to imply type-checking, this distinction is largely irrelevant for booleans. Since Erlang does not perform "magic" type-casting for booleans (e.g., 0 is never equal to true), == and =:= behave identically when one operand is a boolean. Therefore, using =:= true offers no functional advantage over simple logical evaluation.

Furthermore, if type safety is a concern (ensuring the value is actually a boolean), one can use is_boolean(Val) andalso Val instead.

Options

• None.

Example configuration

{elvis_style, no_boolean_in_comparison, #{}}