Re: [Axiom-developer] about Expression Integer

[Ralf Hemmecke]

Hi Bill,

> (4) -> Z:Float:=1
>
>    (4)  1.0
>    Type: Float
>
> (5) -> Z::INT        <---- this is a conversion of Float to INT
>
>    (5)  1
>    Type: Integer

Now, I learned something new. And maybe Axiom behaves here different 
from Aldor.

In Aldor "Z::Integer" is just syntactic sugar for writing
"coerce(Z)@Integer" (which looks for a function

coerce: Float -> Integer

currently in scope and applies it).

In Aldor there is (almost) never a coercion (type cast) done 
automatically. Of course you can write something like

aldor -gloop
#include "aldor"
#include "aldorinterp"
Z:SingleFloat := 1;

But there is no coercion involved. Since SingleFloat is of type 
ArtithmeticType.

%10 >> SingleFloat has ArithmeticType
T @ Boolean
%11 >> ArithmeticType
 @ Category == AdditiveType with
        1: %
        *: (%, %) -> %
        ^: (%, MachineInteger) -> %
        commutative?: Boolean
        one?: % -> Boolean
        times!: (%, %) -> %
        default
                local copy?: Boolean == % has CopyableType
                one?(a: %): Boolean == ..
                times!(a: %, b: %): % == ..

The 1 is simply interpreted as the constant 1 in SingleFloat.

Now the following is also clear.

%14 >> Z := 2
       .....^
[L14 C6] #1 (Error) No meaning for integer-style literal `2'.
%15 >> Z:=2.0
2 @ SingleFloat
%16 >> import from Integer
%17 >> Z := 2
       .....^
[L17 C6] #1 (Error) There is no suitable interpretation for the expression 2
  The context requires an expression of type SingleFloat.
     The possible types of the right hand side (`2') are:
          -- AldorInteger

I like that Aldor does nothing automatically.

Ralf

PS: To be correct there is one case that comes to my mind where the 
Aldor compiler is a bit more relaxed.
See "Curtesy conversions" at
http://www.aldor.org/docs/HTML/chap7.html#6