Errors using abs() with an integer and using type() in student mode

[laurentVeliscek]

Hi !

Using MrPython in student mode, I discovered something that looks like a bug.

here's the code :

def functionWithAbs(a:int)->int:
    """ using abs() with an integer should output an integer !..."""
    return abs(a)

assert functionWithAbs(2)==2

I get the error "return value is a float":

Erreur: ligne 3
==> Type de retour erroné: Le type de retour déclaré pour la fonction 'functionWithAbs' est 'int' mais l'expression du `return` est de type incompatible: float

But in Python, applying abs() to an integer always gives an integer. So this error message a false positive.
(I got crazy when I tried to fix this error)

I noticed that when I tried to force "int" type

# doesn't work
return int(abs(a) // 2)

# but this works... (?)
return int(abs(a)) // 2

By the way, still in student mode, is it normal that you cannot use the type() inside a function ?

type() works fine out of a function body but

def useType(a:int)-> str:
    """ test type"""
    return type(a)

assert useType(2)=="int"

triggers an error: "type() is un unknown function" :

Erreur: ligne 5
==> Problème d'appel: je ne connais pas de fonction dont le nom est 'type'

Notice that I can evaluate "useType(2)" with no problem, even if I get this error...

It's annoying because type() can be useful for debugging purpose.

Thanks for your help.

[fredokun]

There are two questions in one.
For the abs() function, it is currently types float -> float for generality.
However, if I want to use it in an integer position, as e.g. in :

k : int = abs(x)

The typechecker will complain because potentially abs(x) can be a float, hence to avoir any problem
you might write instead :

k : int = int(abs(x))

Of course, you might expect that if x is of type int the conversion would not
be required... But the type-system is not capable of explaining that the
type of abs(x) to be int if x is typed int, or float instead.

One thing I could do is to make abs() a primitive operator similar to +, -, etc.
This is consistent with the fact that it is a primitive function in python.

But be aware that we cannot define such a function "by hand", it must be hardcoded in the typechecker.

Finally, the type() primitive returns an internal representation and not an actual type from the typing module,
and moreover I don't know how to represent types in the typechecker, so it should be phased out in student mode
(don't forget that expert mode is available for this kind of need).