BeginPackage["KnotTheory`"];

HyperbolicVolume; NotHyperbolic;

Begin["`HyperbolicVolume`"]

HyperbolicVolume["Not hyperbolic"] = 
      NotHyperbolic
HyperbolicVolume[
        S_String /; 
          StringMatchQ[S, 
            DigitCharacter ..  ~~ "." ~~ DigitCharacter .. ]] := 
      ToExpression[S]

End[]

EndPackage[]