gno.land/r/moul/x/daily/fractiondemo/v0⧉

1// Package fractiondemo is a small gnoweb demo of the exact rational arithmetic2// provided by the [p/moul/x/daily/fraction](/p/moul/x/daily/fraction/v0)3// library: it shows thirds summing to exactly one, and a comparison that a4// decimal detour would get wrong.5//6// It contains no arithmetic of its own. Stateless, so Render is deterministic.7package fractiondemo89import (10	"strings"1112	"gno.land/p/moul/x/daily/fraction/v0"13)1415// Render renders the demo for gnoweb.16func Render(path string) string {17	var b strings.Builder18	b.WriteString("# Fractions\n\n")19	b.WriteString("Exact rational arithmetic, demoing the ")20	b.WriteString("[`p/moul/x/daily/fraction`](/p/moul/x/daily/fraction/v0) library.\n\n")2122	third, _ := fraction.New(1, 3)23	sum, _ := third.Add(third)24	sum, _ = sum.Add(third)2526	b.WriteString("## A third, three times\n\n")27	b.WriteString("`1/3 + 1/3 + 1/3` = **")28	b.WriteString(sum.String())29	b.WriteString("**, exactly — not 0.9999…\n\n")30	b.WriteString("As a decimal it is only ever an approximation: `")31	b.WriteString(fraction.Decimal(third, 10))32	b.WriteString("`\n")3334	half, _ := fraction.New(1, 2)35	b.WriteString("\n## Arithmetic\n\n| expression | result |\n|---|---|\n")36	add, _ := half.Add(third)37	sub, _ := half.Sub(third)38	mul, _ := half.Mul(third)39	div, _ := half.Div(third)40	row(&b, "1/2 + 1/3", add.String())41	row(&b, "1/2 - 1/3", sub.String())42	row(&b, "1/2 × 1/3", mul.String())43	row(&b, "1/2 ÷ 1/3", div.String())4445	approx, _ := fraction.New(33333, 100000)46	b.WriteString("\n## Exact comparison\n\n")47	b.WriteString("`1/3` vs `33333/100000` — identical to five decimal places, ")48	b.WriteString("yet the library still knows which is larger: **")49	if third.Cmp(approx) > 0 {50		b.WriteString("1/3 is greater")51	} else {52		b.WriteString("33333/100000 is greater or equal")53	}54	b.WriteString("**\n\n")55	b.WriteString("> Comparison cross-multiplies, so it never takes a decimal detour. ")56	b.WriteString("There are no floats here: on a chain, an answer that depends on ")57	b.WriteString("rounding is a consensus bug.\n")58	return b.String()59}6061func row(b *strings.Builder, expr, res string) {62	b.WriteString("| `")63	b.WriteString(expr)64	b.WriteString("` | `")65	b.WriteString(res)66	b.WriteString("` |\n")67}68