simple_fraction

Exact Rational Arithmetic with Fractions and Mixed Numbers

v1.0.0 MIT DbC Enforced

Overview

simple_fraction provides exact rational arithmetic for Eiffel using fractions (numerator/denominator). Perfect for recipes, measurements, probabilities, and any calculation where precision matters.

The Problem with Decimals

Neither floating-point nor decimal can represent 1/3 exactly:

-- Every decimal representation of 1/3 is approximate
1.0 / 3.0  -- 0.33333333... (truncated somewhere)

This means 1/3 + 1/3 + 1/3 may not equal exactly 1!

The Solution

local
    third, total: SIMPLE_FRACTION
do
    create third.make (1, 3)
    total := third + third + third
    print (total.out)  -- "1" (exactly 3/3 = 1)
end

Quick Start

Installation

  1. Set the environment variable: 
    export SIMPLE_EIFFEL=/d/prod
  2. Add to your ECF file: 
    <library name="simple_fraction" location="$SIMPLE_EIFFEL/simple_fraction/simple_fraction.ecf"/>

Basic Usage

class
    RECIPE_SCALER

feature -- Scaling

    triple_recipe (ingredient: STRING): STRING
            -- Triple a fractional ingredient amount
        local
            amount, tripled: SIMPLE_FRACTION
        do
            create amount.make_from_string (ingredient)
            tripled := amount.scale (3)
            Result := tripled.to_mixed_string
        end

end

-- Usage:
scaler.triple_recipe ("2/3")   -- Returns: "2"
scaler.triple_recipe ("1/4")   -- Returns: "3/4"
scaler.triple_recipe ("1 1/2") -- Returns: "4 1/2"

Key Features

Exact Arithmetic

1/3 + 1/3 + 1/3 = 1 exactly. No rounding errors, no approximation.

Auto-Reduction

Fractions automatically reduce to lowest terms. 4/8 becomes 1/2.

Mixed Numbers

Full support for mixed numbers like 2 3/4. Create, display, extract parts.

Smart Parsing

Parse "3/4", "2 3/4", "0.5", or "5" - all work automatically.

Immutable Operations

All arithmetic returns new values. Thread-safe, predictable.

Design by Contract

Full preconditions, postconditions, and invariants throughout.

simple_fraction vs simple_decimal

Feature simple_fraction simple_decimal
Best for Ratios, recipes, probabilities Money, financial, prices
1/3 Exact Approximate
0.1 1/10 (exact) Exact
Output "2 3/4" "$19.99"

Documentation