[vincent-manis]

A Scheme system that implemented exact reals as unnormalized floating decimal (IEEE 754-2008), coupled with a directive that said `numbers with a decimal point should/should not be read as exact' would be wonderful, not just for financial things, but also for teaching students.

[neilv]

It's actually easy to implement that slight variation in Racket, as a `#lang` or reader extension.

As an example of a Scheme-ish `#lang`, here's a Racket `#lang sicp` that I made to mimic MIT Scheme, as well as add a few things needed for SICP: https://github.com/sicp-lang/sicp/blob/master/sicp/main.rkt

It would be even easier to make a `#lang better-scheme`, by defining just a few changes relative to `racket-base`, such as how numbers are read.

[soegaard]

The reader even has a parameter `read-decimal-as-inexact` that controls how to read decimal numbers.

[neilv]

Good point. For exacts in `#lang`, I realized afterwards that it's not just literals/self-evals: there's some "standard library" functions you'd probably want to wrap, to force them to produce exact numbers. And maybe check that there's nothing in standard library that does inexacts internally in a way that would be unpredictable to a programmer who expects exact number behavior.