Sometimes it's hard to believe Felix is SOO dang good!
This works now:
var squares = \{ (?x,?y) : int * int | y == x * x \} ;
println$ (3,9) \in squares;
The general form is
\{ pattern : type | predicate \}
A predicate is any expression evaluating to bool, which may use
the variables in the pattern match. We have to specify the type
of the pattern, and our patterns have ugly ? in them sometimes,
but otherwise this is similar to a mathematical set.
A set_form is a real object. Any object with a method
has_elt: T -> bool
acts like a set courtesy of these definition in std/algebra/set.flx:
interface set_form[T] { has_elt: T -> bool; }
fun \in[T] (elt:T, s:set_form[T]) => s.has_elt elt;
If your object has other methods you can "cast" them away
with a coercion to meet the specification.
It's easy to define the union now:
fun \cup[T] (A:set_form[T], B:set_form[T]) => \{ ?x : T | x \in A or x
\in B \};
I will do some more work on this.
* At present, \{ \} can must be used. It's possible the parser will work with
plain {}
* To display it right you need to go into math mode:
\( \{ (?x,?y) : int * int | y == x * x \} \)
which will also display the \( \) parents ;( I may be able to fix this,
I'm not sure: not all program code looks right in math mode.
* \mid works better than |, whether it should be allowed,
or flx_web should just change the | I don't know (matches
can be used in the expression so it could be confused .. )
--
john skaller
skal...@users.sourceforge.net
http://felix-lang.org
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