[Caml-list] string_of_float (0.1 +. 0.2)

[Kenichi Asai <asai@is.ocha.ac.jp>]

On OCaml 4.12.0 on M1 mac, I got:

# 0.1 +. 0.2;;
- : float = 0.300000000000000044
# string_of_float (0.1 +. 0.2);;
- : string = "0.3"

Why don't I obtain "0.300000000000000044" here?

Here is some background.  I am writing an OCaml interpreter that
mimics most part of the original OCaml interpreter.  In the OCaml
interpreter, 0.1 and 0.2 are represented as

Pexp_constant (Pconst_float ("0.1", None))
Pexp_constant (Pconst_float ("0.2", None))

When I add these two numbers, I would have to execute

let a = float_of_string "0.1"
let b = float_of_string "0.2"
let c = a +. b
let d = string_of_float c

and then return

Pexp_constant (Pconst_float (d, None))

At this point, however, since d is "0.3" instead of
"0.300000000000000044" (even though c is 0.300000000000000044), I
cannot return 0.300000000000000044 as a result.  How can I mimic the
OCaml behavior?

Sincerely,

-- 
Kenichi Asai