E08085: logical expression is always true or always false

What went wrong

This logical expression is always true or always false regardless of the operand value.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 795 (What is a logical tautology and why does EK9 reject it?)

How to fix it

1. Check variable names for typos
2. If always-true is intended, use 'true' directly
3. If always-false is intended, use 'false' directly
4. Simplify the logic to use different variables

Common causes

• Typo (same variable used twice instead of different variables)
• Refactoring error (condition was changed but negation was not removed)
• Misunderstanding of Boolean logic

See also

• E08081: self-comparison
• E08084: redundant Boolean comparison

Examples

Every example is compiled by the EK9 compiler: the first fails exactly as captioned, the others fix it.

Fails with E08085: logical expression is always true or always false

#!ek9
defines module error.e08085.bad

  defines function

    checkOrNotTautology()
      -> isEnabled as Boolean
      <- result as Boolean?

      result: isEnabled or not isEnabled

    checkAndNotContradiction()
      -> isEnabled as Boolean
      <- result as Boolean?

      result: isEnabled and not isEnabled

    checkNotOrTautology()
      -> isEnabled as Boolean
      <- result as Boolean?

      result: not isEnabled or isEnabled

    checkNotAndContradiction()
      -> isEnabled as Boolean
      <- result as Boolean?

      result: not isEnabled and isEnabled

Fixed: Combine different conditions

#!ek9
defines module error.e08085.good

  defines function

    orDifferentVars()
      ->
        first as Boolean
        second as Boolean
      <- result as Boolean?

      result: first or second

    andNotDifferentVar()
      ->
        first as Boolean
        second as Boolean
      <- result as Boolean?

      result: first and not second

    bothNegatedDifferent()
      ->
        first as Boolean
        second as Boolean
      <- result as Boolean?

      result: not first or not second

Questions and answers

These Q&A entries show E08085 and its fix:

• Q795: What is a logical tautology and why does EK9 reject it?