create valid float string in scientific notation

[kbkpbot]

Describe the bug

In scientific notation of float, it should not omit the 0 between . and e.
e.g.
1.0e+10, but not 1.e+10

Although in C and Go, 1.e+10 is a valid format.

This is related to issue #26043

Reproduction Steps

f.v

module main

fn main() {
        val1 := 1.e+10
        val2 := 1.0e+10

        str1 := '${val1}'
        str2 := '${val2}'

        dump(str1)
        dump(str2)
}

v run f.v

Expected Behavior

$ v run f.v
[f.v:10] str1: 1e+10
[f.v:11] str2: 1e+10

Current Behavior

$ v run f.v
[f.v:10] str1: 1.e+10
[f.v:11] str2: 1.e+10

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.12 1cdb0f5.8b423a4

Environment details (OS name and version, etc.)

V full version	V 0.4.12 1cdb0f5.8b423a4
OS	linux, Ubuntu 24.04.3 LTS
Processor	8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-9700 CPU @ 3.00GHz
Memory	11.02GB/15.51GB
V executable	/media/HD/github/kbkpbot/v/v
V last modified time	2025-12-20 01:26:49
V home dir	OK, value: /media/HD/github/kbkpbot/v
VMODULES	OK, value: /home/mars/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/mars/v/bug/json
Git version	git version 2.43.0
V git status	weekly.2025.46-247-g97445433
.git/config present	true
cc version	cc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
gcc version	gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
clang version	Ubuntu clang version 18.1.3 (1ubuntu1)
tcc version	tcc version 0.9.28rc 2025-02-13 HEAD@f8bd136d (x86_64 Linux)
tcc git status	thirdparty-linux-amd64 696c1d84
emcc version	N/A
glibc version	ldd (Ubuntu GLIBC 2.39-0ubuntu8.6) 2.39

[JalonSolov]

Many computer languages support floating point with no digits after the period, but the JSON spec says there must be a digit after the period. See "Numbers" in https://ecma-international.org/wp-content/uploads/ECMA-404.pdf and Section "6. Numbers" in https://www.rfc-editor.org/rfc/rfc8259.txt

[jorgeluismireles]

Yes, the JSON spec requires a number between . and e/`E. I was working for a custom parser for JSON and parse the numeric element with and state machine like this:

                         ╭──────────────────────╮
│ 0        1  ╭───╮  2   │  ╭───╮ 4  ╭─────╮ 5  │                                      │
├─╮───────╭─╮─┤ 0 ├────╭─╯──┤ . ├──╭─┤ 0_9 ├──╮─╰╮──────────────────────────────────╭──┤
│ │ ╭───╮ │ │ ╰───╯    │    ╰───╯  │ ╰─────╯  │  │ ╭───╮                            │  │
  ╰─┤ - ├─╯ │ ╭─────╮ 3│           ╰──────────╯  ╰─┤ e ├─╮6   ╭───╮                 │
    ╰───╯   ╰─┤ 1_9 ├─╭╯─────────╮               │ ╰───╯ │  ╭─┤ + ├─╮               │
              ╰─────╯ │  ╭─────╮ │               │ ╭───╮ │  │ ╰───╯ │  7  ╭─────╮   │
                      ╰──┤ 0_9 ├─╯               ╰─┤ E ├─╰─╮╯───────╰─╭─╭─┤ 0_9 ├─╮─╯
                         ╰─────╯                   ╰───╯   │  ╭───╮   │ │ ╰─────╯ │8
                                                           ╰──┤ - ├───╯ ╰─────────╯
                                                              ╰───╯

https://gitlab.com/jmireles/viva/-/blob/main/coding/json/parser.v?ref_type=heads#L251

I tried this approach because I have some problems with x.json2, but I learned is too much work and I haven't conclude with my experiments in JSON and now I am involved in another issues.