Number Types¶
Numbers can be of type Number and Int. Both are represented as normal JavaScript numbers at runtime. Int, however, has operations defined differently so that we always get integer results:
> div 7 2
3
> mod 7 2
1
> div 7.0 2.0
3.5
> mod 7.0 2.0
0.0
Note how div 7 2 results in 3, rather than 3.5. A number without a decimal is always considered an Int, while a number with a decimal is always considered a Number. Exponential notation always means the type is Number:
> 1
1
> :type 1
Int
> 1.0
1.0
> :type 1.0
Number
> 1e0
1.0
> :type 1e0
Number
> 1e-2
0.01
> :type 1e-2
Number
They Int-typed operations are made to return integers with some use of bitwise operators, as we can see in .spago/prelude/v6.0.0/src/Data/Ring.js:
export const intSub = function (x) {
return function (y) {
return x - y | 0;
};
};
Typing a number¶
As we saw, 1 is Int, while 1.0 or 1e0 is Number. We cannot force a value like 1 to be Number simply by adding a type annotation like in Haskell.
n :: Number
n = 1
The above will produce an error:
Could not match type
Could not match type
Int
with type
Number
while checking that type Int
is at least as general as type Number
while checking that expression 1
has type Number
in value declaration n
PureScript(TypesDoNotUnify)
Negative Numbers¶
To make negative numbers, use the unary - operator (requires parenthesis) or the negate function.
> 1 + (-1)
0
> 1 + negate 1
0