ST Parser
View SourceA simple, lightweight, flexible parser for Session Types in Elixir.
ST Parser converts textual session type descriptions into typed Elixir data structures, enabling formal verification and implementation of communication protocols between distributed system components.
What are Session Types?
Session types provide a way to formally describe communication protocols between different roles in a distributed system. They let you specify:
- Who sends messages to whom
- What data is exchanged in those messages
- The order of interactions
- Choices and branches in the protocol flow
Features
- Parse session type expressions into structured Elixir terms
- Build session types programmatically with constructor functions
- Handle complex session type constructs like input (external choice) and output (internal choice)
- Support nested payload types (lists, tuples)
- Clean and simple API for integration into larger projects
Installation
Add st_parser
to your list of dependencies in mix.exs
:
def deps do
[
{:st_parser, "~> 0.4.1"}
]
end
Usage
Parsing Session Type Expressions
# Parse a session type string into a structured type
{:ok, session_type} = ST.Parser.parse("&Server:{ Ack(unit).end }")
# Or use the bang version which raises on error
session_type = ST.Parser.parse!("&Server:{ Ack(unit).end }")
# Parse just a payload type
{:ok, payload_type} = ST.Parser.parse_type("(string, boolean[])")
Building Session Types Programmatically
# Create an End type
end_type = ST.end_session()
# Create a simple branch
ack_branch = ST.branch(:ack, :unit, end_type)
# Create an input type (receiving a message)
input_type = ST.input(:server, [ack_branch])
# Or more concisely:
input_type = ST.input_one(:server, :ack, :unit, end_type)
# Create an output type (sending a message)
output_type = ST.output_one(:client, :request, :binary, end_type)
Session Type Syntax
Session type expressions use a concise syntax:
# Input (receiving messages)
&Role:{ Label1(PayloadType).Continuation, Label2(PayloadType).Continuation }
# Output (sending messages)
+Role:{ Label1(PayloadType).Continuation, Label2(PayloadType).Continuation }
# Termination
end
Payload types can be:
- Basic types:
string
,number
,boolean
,unit
- List types:
type[]
(e.g.,string[]
) - Tuple types:
(type1, type2, ...)
(e.g.,(string, number[])
)
Example: A Simple Request-Response Protocol
request_response = """
&Server:{
Request(string).+Client:{
Response((string, number[])).end,
Error(string).end
}
}
"""
{:ok, protocol} = ST.Parser.parse(request_response)
This describes a protocol where:
- The user sends a
Request
with a string payload to the server - The client responds with either:
- A
Response
containing a tuple of a string and a number array, then ends - An
Error
with a string message, then ends
- A
Documentation
Full documentation is available via ExDoc:
mix docs