Variable value

[Raknarg]

Is there a way to have an if statement seeing if a variable has no value?

Turing:

if has_value (x) = false then      do_something () end if

[[Gandalf]]

As far as I remember, Turing doesn't default initialize variables. So it's more of a design issue, since trying to reference an uninitialized variable will fail at compile time. Usually you would initialize your value x to some sentinel value and check for that...

Turing:

var x : int := -1 if x = -1 then      do_something () end if

The key here is that -1 has no meaning for "normal" values of x. If the use case isn't trivial, you can consider making x an object, and keep track of its initialization state in a member variable.

[Raknarg]

Thats true, but the way my program wad weird, it was hard to reference specific variables. Linked lists are weird I got around it though.

[Dreadnought]

It is possible to detect if a variable is initialized or not. Turing saves one bit representation in each type for this, we just have to find out what it is and get Turing to check it. Here's a way of doing it for the more common built-in types:

Turing:

const strUnInit := 16#80 const intUnInit := 16#80000000 const realPartUnInit := 16#80000000 const boolUnInit := 16#FF /* The char type does not have an uninitialized value,  When declared, a char is given the value of the zero  character chr(0) or '/0'  */ var a : char % := '\0' var b : string if #b = strUnInit then     put "String named 'b' is not initialized" else     put "String named 'b' is initialized" end if var c : int if #c = intUnInit then     put "Integer named 'c' is not initialized" else     put "Integer named 'c' is initialized" end if var d : real if nat4@(addr(d)) = realPartUnInit and nat4@(addr(d)+ (sizeof(real) div 2)) = realPartUnInit then     put "Real named 'd' is not initialized" else     put "Real named 'd' is initialized" end if var f : boolean if #f = boolUnInit then     put "Boolean named 'f' is not initialized" else     put "Boolean named 'f' is initialized" end if

If you find any bugs let me know.

If you want to try stuff out yourself, here's a function that will print 32 bits.

Turing:

% Calls to printBits should be made with a # in front of the argument % Example: printBits(#arg) % The # is a cheat to nat proc printBits (N : nat4)     for decreasing i : 31 .. 0         put sign (N & (1 shl i)) ..     end for     put "" end printBits

Hope, this helps.

[Dreadnought]

I'd like to add a check for pointers (might be helpful for lists).

Turing:

const ptrUnInit := 16#FFFFFFFF var g : ^anyclass if #g = ptrUnInit then     put "Pointer named 'g' is not initialized" else     put "Pointer named 'g' is initialized" end if

[Tony]

pointers should be initialized (manually, if needs be) to null (which is 0). Null-Pointer Exceptions are much much much easier to figure out and solve, than random segfaults where the program just grabs a random piece of memory and runs with it as if it was a valid object, until something else breaks.