Question regarding the syntax of "is"

[Fredo Erxleben‏]

Hello there!

First, congratulations on the release of version 1.2

I have been following the development of the language and its features for a moment, and there is a little thing that bugs me:

Why is the syntax for the type checking
  

is (type name) (variable name)

?

Wouldn't it be far more readable to have an infix operator like

(variable name) is (type name)

, especially in combinations with assertions or assignments?

Disclaimer: I am aware that this is linguistic nit-picking and that there are quite good reasons for how things are… I merely have not found a satisfying answer for myself.

[Tom Bentley‏]

I think this is what you're asking http://ceylon-lang.org/documentation/1.2/faq/language-design/#prefix_form_for_is_type_exists_and_nonempty

Cheers,

Tom

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[Lucas Werkmeister‏]

However, that page doesn’t mention that `variable is Type` is actually legal syntax. The difference is that the postfix form is a regular expression which doesn’t narrow the type while the prefix form is a *condition* (not an expression by itself) which does narrow the type.

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[Fredo Erxleben‏]

This indeed was my issue.

I so far never thought about this kind of mixing expressions, since I find them terribly unreadable.
Also I would rather write

!(is Person mike)
// or, in the unsupported syntax:
!(mike is Person)

and introduce parenthesis for readability. I am aware you can't enforce this though. And introducing the keyword isnot wouldn't probably be the best way either.

Well, I suppose I will have to live with this kind of syntax and ignore my grammar sense tingling all the time :)

But thanks for the clarification.