contract Shop                      # 1. header: always the first line of code

const MAX_NAME: int = 64           # 2. constants
state owner: address               # 3. state variables
state prices: map[text, int]
event Sold(item: text, buyer: address, price: int)   # 4. events

init():                            # 5. functions: init, action, view, fn
    owner = caller

action set_price(item: text, price: int):
    require caller == owner, "only the owner"
    require valid_name(item), "item names have 1 to 64 bytes"
    require price >= 0, "price cannot be negative"
    prices[item] = price           # a price of 0 removes the item

action buy(item: text) payable:
    require prices.has(item), "unknown item"
    require value == prices[item], "wrong price"
    send(owner, value)
    emit Sold(item, caller, value)

view price_of(item: text) -> int:
    return prices[item]

fn valid_name(item: text) -> bool:
    return len(item) >= 1 and len(item) <= MAX_NAME