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Cat: Namespaces and Type Annotations

2 replies on 1 page. Most recent reply: Jul 18, 2006 10:30 AM by Christopher Diggins

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Christopher Diggins

Posts: 1215
Nickname: cdiggins
Registered: Feb, 2004

Cat: Namespaces and Type Annotations (View in Weblogs)
Posted: Jul 17, 2006 2:00 AM
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Summary
The next version of the Cat programming language, contains namespaces and type annotations.
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The upcoming version of Cat, which is still undergoing testing, implements type annotations and namespaces.

The type annotation of Cat is based on the idea that every program, or subprogram, is a transition from one stack to another. For example the following is the type annotation for several of the atomic programs of Cat (the primitives if you prefer):

  + : (int int) -> (int)
  - : (int int) -> (int)
  and : (bool bool) -> (bool)
  > : (int int) -> (bool)
  pop : (any) -> ()
  dup : (any) -> (any any)
Some programs have side-effects, and these are annotated differently:
  rnd : () ~> (int)
  write : (any) ~> (any)  
A program which has no side-effects, is called a function, whereas a program with side-effects is called a subroutine.

Cat now also supports scopes. A namespace is just a named scope. This addition makes it much easier to write non-trivial software using Cat.

Here is what some sample programs look like in the upcoming Cat:

define clear : (any*) ~> ()
{
  [pop] [is_stack_empty not] while
}

define simple_test : () -> (int)
{
  0 1 +
}

define nested_test : () -> (int)
{
  define f : () -> (int)
  {
    1
  }

  define plus_one : (int) -> (int)
  {
    1 +
  }

  f plus_one
}

namespace X
{
  define f : (int) -> (int)
  {
    2 +
  }
}

namespace Y
{
  define f : (int) -> (int)
  {
    3 +
  }
}

define main : () ~> ()
{
  "expect 1" write simple_test write clear
  "expect 2" write nested_test write clear
  "expect 3" write 1 X.f write clear
  "expect 4" write 1 Y.f write clear
}


Tim LS

Posts: 37
Nickname: parchandri
Registered: Jul, 2005

Re: Cat: Namespaces and Type Annotations Posted: Jul 17, 2006 9:16 PM
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I am curious about why Clear is annotated as (any*) ~> (), and not (any*) -> ().

Christopher Diggins

Posts: 1215
Nickname: cdiggins
Registered: Feb, 2004

Re: Cat: Namespaces and Type Annotations Posted: Jul 18, 2006 10:30 AM
Reply to this message Reply
> I am curious about why Clear is annotated as (any*) ~> (),
> and not (any*) -> ().

My reasoning is because it consumes a variable number of stack elements. If it called as part of a conditional, it would leave the stack in an unstable state.

Maybe this is not the right thing to do?

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