FYI: Ceylon

[Paul D. Anderson]

I took a quick look at the Ceylon language 
(http://ceylon-lang.org/) which is supposed to be a follow on to 
Java (they disavow the name "Java Killer" <wink, wink, nudge, 
nudge>).

One of their design goals is "familiar, readable syntax", but 
they seemed to have missed the boat on that one. Their type 
system is Byzantine and it is the heart of the language.
But I thought this little fragment from their spec dealing with 
type constraints was interesting:

(The words "given", "satisfies", "abstracts", "of" and "is" are 
keywords.)

<quote>
There are five different kinds of type constraint:

• an upper bound, given X satisfies T, specifies that the type 
parameter X is a subtype of a given type T,

• a lower bound, given X abstracts T, specifies that a given 
type T is a subtype of the type parameter X,

• an enumerated bound, given X of T|U|V specifies that the type 
parameter X represents one of the enumerated types,

• a parameter bound, given X(...) specifies that the type 
parameter X is a concrete class with the given parameter types, 
and

• a metatype bound, given X is T, specifies that the concrete 
metatype of the type parameter is a subtype of a given type T.
</quote>

They also have couple of operators, '===' and '<=>' meaning 
'identical' and 'compare', respectively. They have an identity 
operator but also have the keyword 'is', which should give you an 
inkling of the languages complexity. I assume 'compare' is the 
same as D's 'opCmp', and it strikes me as a useful operator. 
(Although I think the unusual comparison operators in D ('!<>=') 
wound up high on the list of the "too many features" post.

Paul