libretto.examples

Reads lines from standard input and prints them to standard output.

This example implements interaction between two parties, Alice and Bob, in which

• Alice sends "ping" to Bob,
• Bob sends "pong" back to Alice,
• Alice sends Done to Bob,

in this order, after which no more interaction between the two takes place.

This example demonstrates:

• A simple protocol between two parties.
• Linearity: obligation to consume every input exactly once and fulfill every demand exactly once. Linearity is key to ensuring adherence to a protocol.
• Inverting the flow of values from left-to-right to right-to-left and vice versa.

This example implements interaction between two parties, Alice and Bob, in which

• when it's Alice's turn, she can choose to send "ping" to Bob or to quit;
• when it's Bob's turn, he can choose to send "pong" back to Alice, or to quit;
• interaction continues until one of the parties quits.

This is an extension of the PingPong example to multiple rounds of ping-pong. It further demonstrates:

• The choice operators |+| and |+|.
• Recursive protocol type.

N scientists sharing M microscopes (N > M).

This examples demonstrates:

• concurrency (scientists operate concurrently)
• sequencing (each scientist performs experiments sequentially, at most one at a time)
• resource sharing via pooling (the limited number of microscopes is made available throught a pool)

In a pandemic, supermarkets are required to limit the number of customers in the store. A way to do this is to provide a limited number of shopping baskets and require that each customer entering the store has a shopping basket. When there are no more baskets, an incoming customre has to wait for a previous customer to leave (and return their basket).

This example demonstrates:

• concurrency
  • customers come and shop concurrently
• sequencing
  • a customer can shop only after obtaining a basket
  • a customer can use an item only after paying for it
  • ...
• mutual exclusion
  • limited number of concurrently shopping customers
    • without side-effects on shared synchronization objects (such as semaphores)
• linear & session types
  • obligation to return a basket enforced by the type-system
  • the type Shopping is a protocol between the store and the customer