lemma 0.9.2

A pure, declarative language for business rules.
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spec coffee_order
"""
Coffee Shop Pricing

A simple example showing how data and rules work together.
Perfect for understanding the basics of Lemma.
"""

data money: measure
  -> decimals 2
  -> unit eur 1.00
  -> unit gbp 1.17
  -> minimum 0 eur

data product: text
  -> option "espresso"
  -> option "latte"
  -> option "cappuccino"
  -> option "mocha"

data size: text
  -> option "small"
  -> option "medium"
  -> option "large"

data age: number
  -> maximum 100
  -> minimum 0

data number_of_cups: number
  -> maximum 10

data has_loyalty_card: boolean

rule base_price: veto "Unknown type of coffee"
  unless product is "espresso"   then 2.5 eur
  unless product is "latte"      then 3.5 eur
  unless product is "cappuccino" then 3.5 eur
  unless product is "mocha"      then 4 eur

rule size_multiplier: veto "Unknown size of coffee"
  unless size is "small"  then 80%
  unless size is "medium" then 100%
  unless size is "large"  then 120%

rule price_per_cup: base_price * size_multiplier

rule subtotal: price_per_cup * number_of_cups

rule loyalty_discount: 0%
  unless has_loyalty_card then 10%

rule age_discount: 0%
  unless age >= 65 then 10%

rule combined_discount: loyalty_discount + age_discount

rule discount_amount: subtotal * combined_discount

rule total: subtotal - discount_amount