Variables in Standard ML

In Standard ML, variables are typically declared and initialized in one step. The language uses type inference to determine the types of variables.

```sml
(* Declare and initialize a variable *)
val a = "initial";
print (a ^ "\n");

(* Declare multiple variables at once *)
val (b, c) = (1, 2);
print (Int.toString b ^ " " ^ Int.toString c ^ "\n");

(* Standard ML will infer the type of initialized variables *)
val d = true;
print (Bool.toString d ^ "\n");

(* Variables declared without initialization are not allowed in Standard ML *)
(* Instead, we can use option types for potentially uninitialized values *)
val e : int option = NONE;
print (case e of
           SOME x => Int.toString x
         | NONE => "NONE"
);
print "\n";

(* Standard ML doesn't have a := syntax for declaration and initialization *)
(* Instead, we use val for both declaration and initialization *)
val f = "apple";
print (f ^ "\n");

To run this Standard ML program, you would typically save it to a file (e.g., variables.sml) and then use an SML interpreter or compiler. For example, if you’re using Standard ML of New Jersey (SML/NJ), you could run it like this:

$ sml variables.sml
initial
1 2
true
NONE
apple

In Standard ML:

Variables are immutable by default. Once a value is bound to a variable, it cannot be changed.
There’s no need for explicit type declarations in most cases due to type inference.
Standard ML doesn’t have a concept of “zero values” like Go does. Instead, for potentially uninitialized values, we use option types.
The language doesn’t have a special syntax for short variable declarations. All variable bindings use the val keyword.
Standard ML is a functional programming language, so it approaches some concepts differently from imperative languages like Go.

Values in Standard ML

Constants in Standard ML

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Variables in Standard ML