Even more:

If a function takes a number—whether it's an integer, a floating-point base-2 number, or a Dec—you can always write 5 as the number you're passing in. (If it's an integer, you'll get a compiler error if you try to write 5.5, but 5.5 will be accepted for either floats or decimal numbers.)

Because of this, it's actually very rare in practice that you'll write 0.1 + 0.2 in a .roc file and have it use the default numeric type of Dec. Almost always, the type in question will end up being determined by type inference—based on how you ended up using the result of that operation.

For example, if you have a function that says it takes a Dec, and you pass in (0.1 + 0.2), the compiler will do Dec addition and that function will end up receiving 0.3 as its argument. However, if you have a function that says it takes F64 (a 64-bit base-2 floating-point number), and you write (0.1 + 0.2) as its argument, the compiler will infer that those two numbers should be added as floats, and you'll end up passing in the not-quite-0.3 number we've been talking about all along.