5.1 Variables

Felix provides a way to create variables using the var binder. Again using the bindings from the first and second chapters:

  include './intro_02';

hello world
3
mytrue
3
2

Note that since {intro_02.flx} includes {intro_01.flx} both get included by {include './intro_02';}.

5.1.1 The `var` binder

We will now show you the var binder. We'll repeat the code, using variables:

  var hello-world = mycat (mycat (hello, white), world); 
  myprint (hello-world); myendl();
  
  // show 1 + 2, should be 3
  var thre = (myadd (one, two));
  myprintln (thre);
  
  // basic axiom check
  var onetwo = myadd (one, two);
  var twoone = myadd (two, one); 
  var ok = myeq (onetwo, twoone);
  
  myprint (ok); myendl();

hello world
3
mytrue

Note the spelling {hello-world}. Felix allows hyphens in identifiers. So be careful not to write {x-1} and expect that to be considered a subtraction!

5.1.2 Simple Assignment

Variables can be assigned new values. For example:

  var x = one;
  myprintln (x);
  x = two;
  myprintln (x);

1
2

The var binder requires either a type or an initialiser or both. Here's an example:

  var y : myint = two;
  var z = myadd(y,one);
  var u : myint;
  u = myadd(z,one);
  myprintln (u);

The first line shows a variable initialised by two and the type myint given. This serves and an extra check on the type.

On the second line we allow the type of the RHS expression to determine the variable type.

On the third line, we have an uninitialised variable of type myint. Use of variables before a value is stored in them may have unpredictable results.

5.1 Variables

5.1.1 The var binder

5.1.2 Simple Assignment

5.1.1 The `var` binder