[gambit-list] API to parse floats in Scheme

Lassi Kortela lassi at lassi.io
Wed May 12 15:43:16 EDT 2021

We are planning a simple SRFI to mae floats from integers (or from 
strings), since that's useful when parsing any kind of text syntax that 
has real numbers. The details are implementation-dependent and tricky to 
get right.

Here's the spec we have so far: https://github.com/pre-srfi/make-float

The API is:

(inexact-real-from-strings  int frac             precision exp) -> real
(inexact-real-from-integers int frac frac-length precision exp) -> real

Example usage:

(inexact-real-from-strings  "-123" "45"  'e "6")  ; => -123.45e6
(inexact-real-from-integers  -123   45 2 'e  6)   ; => -123.45e6

The 2 in the last example means two decimal places. It's needed to 
disambiguate between .6 .06 .006 .0006 etc.

There are both math and Scheme wizards on this list. Could someone 
verify whether this is a sane design before we submit the SRFI draft? 
It's been ok'd by one mathematician already so I'm hopeful :)

There's also an inverse API to serve as a backend for string formatting 

(strings-from-inexact-real  real frac-length) -> int; frac; exp
(integers-from-inexact-real real frac-length) -> int; frac; exp

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