let symbol_of_string = fun s ->
match s with
|"+" -> Add
|"-" -> Sup
|"*" -> Mul
|"/" -> Div
|"_" -> Pass
|"!" -> Stop
|"mem" -> Mem
|"@" -> Delay
|"floor" -> Floor
|"int" -> Int
|"sin" -> Sin
|"cos" -> Cos
|"atan" -> Atan
|"atantwo" -> Atantwo
|"sqrt" -> Sqrt
|"rdtable" -> Rdtable
|"%" -> Mod
|"vectorize" -> Vectorize
|"#" -> Concat
|"[]" -> Nth
|"serialize" -> Serialize
|">" -> Larger
|"<" -> Smaller
|"prefix" -> Prefix
|"selecttwo" -> Selecttwo
|"selectthree" -> Selectthree
| _ -> raise Symbol_not_defined