Displaying integer-valued real numbers

[mbillingr]

The interpreter prints real numbers like integers if their fractional part is zero.
Example:

>> 1.0
1

With small numbers this is no big deal but it may cause confusion if the fractional part is lost due to the limited precision of the floating point representation.

>> (define a 1234567890.12)
>> (* a a)
1524157875315348200

1524157875315348200 looks like an integer, when in fact it is a floating point number with limited precision. Printing the number as 1524157875315348200.0 would communicate that fact more clearly.
Thank you @pgl10 for reporting!

I can see several options to fix this:

• (easy) Use the debug formatter, which prints floats with .0 at the end but never uses scientific notation (Example).
• (easy) Wait for the {:g?} format switch which may never come.
• (moderate) Implement custom formatting to properly show the available precision.
• (trivial) Leave as it is, arguing that the user should not be concerned with the internal implementation of numbers. This argument breaks down for large numbers.

At the moment, I prefer the first option. The trailing zeros are a bit ugly for large numbers but it's so easy to implement.

Any thoughts?

[pgl10]

It is not so easy to display always a real number as a real. Sometimes it looks like an integer. I know a way to display always a real number as a real in C++ and I let you know about this, but I don't know Rust.

[mbillingr]

I think there is an easy way in Rust to it. Otherwise I'll try to adopt your C++ solution.

[mbillingr]

Implemented in f2a781f