Curl primitive never-returns

The docs for the Curl package CURL.LANGUAGE.CORE-TYPES cover a distinctive primitive: never-returns

There is an example by Chris Barber here.

The IDE docs example is in a Curl live-docs {example } macro for running/editing/saving doc code snippets and goes like this

{define-proc {not-odd-error i:int}:never-returns
    {error {format "%s is not odd", i}}
}
{define-proc {assert-odd val:int}:int
    {return
        {if {bit-and val, 1} == 1 then
            val
         else
            {not-odd-error val}
        }
    }
}

 It is not at all the same as the language primitive named void.

Which somehow brings me round to JavaScript and new.

In Curl, the programmer is not required to use the {new } macro - and using it requires another comma in a declaration.

So why ever use {new MyObject, my_args} ?

It might be this: what MyObject is specifying for the macro is a type - and that type may be determined at runtime.  This is not what you usually expect in a language that is "typed" - but this is a language which also has an any type.

So one step further: in Smalltalk the issue is to know who should implement new and basicNew and new:

But in Curl, new is also a method: it is a method of 3 classes in the package  CURL.LANGUAGE.REFLECTION

Constructor
Factory
InstanceMaker

Here is what the docs say about InstanceMaker:

public abstract sealed InstanceMaker {inherits ClassMember}
Package: CURL.LANGUAGE.REFLECTION
Direct Known Subclasses: Factory, Constructor
The representation of a Constructor or Factory for objects of some class.
Notes
See ClassType.

Note that the {new } macro is from the package: CURL.LANGUAGE.COMPILER
Which somehow brings me to {let  ...} {set  ...} and {def  ...} ... and {value  ...}

I recently posted a Rebol tyro puzzler
   p: 42 lst: [p ] what: first lst ; What is the value of :what ?

There is a great little bit in Icon about assignments which do not occur and assignments which reverse when an expression does not succeed. Like Rebol and Curl, Icon is expression-based.  But what huge differences in the paradigms of these three unusual languages. Icon has the prefix dot for de-referencing and Rebol has the word reduce.

let and def are primitives of the Curl language; set, however, is a macro - as are {value ...} and {do ...}.

In some ways, the Curl docs articles on let and value are a great introduction to the language ( def came to Curl only recently.)

What I have found is that it is not all so very clear to neophytes just what is meant by "top-level" code.

Let's take the case of a Curl applet intended for a web browser.  The content of the Curl applet is found in a document which will be one of 3 possible types.  the default type need not be declared and is DefaultDocument.

Someone new to Curl places a {VBox } as declarative Curl in a pristine applet, runs it and nothing appears in the browser.  Or is that so?  This is why I always have my windowing environment on an OS flip my default window backgrounds to some pleasant shade of green: when a browser pane shows me that green background - even if just in some text entry field - I know that something is missing.  The default Curl document background is white.  My demo strategy is this: make things explicitly and declare things explicitly.

{curl 7.0 applet}
{curl-file-attributes character-encoding = "utf8"}
{applet
   name="top level demo",
   notes="like rebol, add most any metadata tag - this one is called       notes"}
{document-style DefaultDocument}
{set-document-properties background =
    {Background.from-string "blue"}}
{title heading? = false, Demo}

{VBox
   {text {value 65535 + 42}},
   {paragraph btw, 6782865577 is prime},
   {text So, what was the question?},
   {new HBox, {paragraph this is just some text ...}}
}

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