Python Sanity Proposal: Type Hinting Solution

[Rustom Mody]

On Friday, January 23, 2015 at 6:45:39 AM UTC+5:30, Rick Johnson wrote:
> Note: This is the closest you're going to get to a PEP from me! 
> 
> Okay, i have found a solution to the type hinting problem 
> that will appease both sides. On one side we have those who 
> are proposing type hinting annotations within function sigs, 
> and on the other side, we have those who oppose the 
> implementation of type hinting via this method because of 
> the readability concerns. The solution is move the type 
> hinting syntax completely out of the source file and into 
> another file -- think of it as a "Python Type Hinting Header 
> File". 
> 
> ============================================================ 
>  Summary 
> ============================================================ 
>   
> (1) Agree on a file extension that python will recognize 
> as containing "type hint specs". Unfortunately we cannot 
> use ".pth", which would be the perfect acronym for "Python 
> Type Hints", so choose something else. :-( 
> 
> (2) Define a spec for writing annotations that will map to 
> funcs/methods of the same name. I would argue to keep the 
> spec compact, but i really don't care about the spec at 
> this point. 
> 
>       
> ============================================================ 
>  Simplistic Example Code utilizing two files: 
> ============================================================ 
> 
>   # 
>   # scriptA.py 
>   # 
>   def greeting(name): 
>       return 'Hello ' + name 
>       
>   #     
>   # scriptA.typehints 
>   # 
>   greeting{name:str} -> str 
> 

1. Allow in same file
2. Chage syntax slightly to
type greeting : str -> str

[type is the keyword equivalent to your other typehint file ]
 and you have essentially the Haskell solution.

The catch I expect is that haskell is strongly committed to simultaneous
definitions:

x = 1
y = x+2

is the same as
y = x+2
x = 1

and so definitions can generally be permuted around

Python is committed to the opposite extreme:
even def and class are not declarative but imperative