how to use ruby " case ... when " with inequalities?

You are mixing two different types of case statements:

case varwhen 1  dosomethingwhen 2..3  doSomethingElseendcasewhen var == 1   doSomethingwhen var < 12   doSomethingElseend

   case myvar     when  proc { |n| n < -5 }        do somethingA     when -5..-3        do special_something_XX     when -2..-1        do special_something_YY     when proc { |n| n == 0 }        do somethingB     when proc { |n| n > 0 }        go somethingC     end   end

I am not personally convinced that you wouldn't be better off with if statements, but if you want a solution in that form:

Inf = 1.0/0case myvarwhen -Inf..-5  do somethingAwhen -5..-3  do special_something_XXwhen -2..-1  do special_something_YYwhen 0  do somethingBwhen 0..Inf  do somethingCend

My preferred solution follows. Here the order matters and you have to repeat the myvar, but it's much harder to leave out cases, you don't have to repeat each bound twice, and the strictness (< vs <= rather than .. vs ...) is much more obvious.

if myvar <= -5  # less than -5elsif myvar <= -3  # between -5 and -3elsif myvar <= -1  # between -3 and -1elsif myvar <= 0  # between -1 and 0else  # larger than 0end