E08087: condition is always false based on data flow analysis

What went wrong

This condition is always false based on the values assigned to variables on this code path. The compiler tracks variable assignments and can determine that this comparison will never be satisfied, making the if-body unreachable dead code.

A guard over a Boolean is a truth guard: in an 'if' / 'else if', 'if ok <- check()' enters only when ok is SET AND TRUE. So 'if ok <- false' (or 'if ok <- Boolean()', which is unset) never enters, and 'then not ok' after such a guard is always false.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 796 (Why does EK9 reject comparisons against variables with kn...)

How to fix it

1. Remove the unreachable condition and its body
2. Check if the variable should have been assigned a different value
3. Verify this isn't a copy-paste error with an incorrect comparison value
4. Check if a reassignment is missing between the assignment and the condition

Common causes

• Variable assigned a constant but compared to a different constant
• Applies to all literal types: Integer, Float, Character, String, Date, Time, DateTime, Millisecond
• Contradictory conditions (e.g., checking x < 0 after throwing on x < 0)
• Refactoring changed an assignment but not the corresponding condition
• Dead switch case where an earlier case always matches
• 'if ok <- false' or 'then not ok' after 'if ok <- check()' — a Boolean guard enters only when ok is true

See also

• E08082: comparison between literal values (both operands are literals)
• E08086: condition always true (dead else instead of dead if-body)
• E08085: logical tautology (structural pattern like 'a and not a')

Examples

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

Fails with E08087: condition is always false based on data flow analysis

#!ek9
defines module error.e08087.bad

  defines constant
    MANY <- 10
    FEW <- 3

  defines function

    classify()
      -> count as Integer
      <- rtn as String: "some"
      if count > MANY and count < FEW
        rtn: "impossible"

    describe()
      <- rtn as String: "unknown"
      status <- "ready"
      if status == "error"
        rtn: "failed"

Fixed: Test a value that can vary

#!ek9
defines module error.e08087.good

  defines constant
    MANY <- 10
    FEW <- 3

  defines function

    classify()
      -> count as Integer
      <- rtn as String: "some"
      if count > MANY or count < FEW
        rtn: "outside"

    describe()
      -> status as String
      <- rtn as String: "unknown"
      if status == "error"
        rtn: "failed"

Questions and answers

These Q&A entries show E08087 and its fix:

• Q796: Why does EK9 reject comparisons against variables with known constant values?