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PlusCal AST and builder in Python
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PlusCal AST and builder in Python

What Is This?

PlusCal is an algorithm language that compiles into a TLA+ specification. This library defines Python types that form an abstract syntax tree (AST) of the PlusCal P-Syntax grammar as well as a builder API for fluently constructing algorithms. The implementation leans heavily on Python dataclasses and type-hinting; a type checker (e.g. mypy) can be used to validate the grammar.

It is anticipated that this library will be used both by humans and by programs to construct grammatically correct specifications and run them through the TLC model checker.


Install from pip:

pip install pluscal

Create an algorithm:

>>> from pluscal.api import Algorithm, Print, Variable

>>> algorithm = Algorithm(
    Variable("s").in_set("Hello", "World!"),
    Print("s", label="A"),

>>> print(algorithm)
--algorithm hello_world
variable s \in {"Hello", "World!"};
    print s;
end algorithm


This library is not complete. Some known limitations include:

  1. The lower-level TLA+ grammar used by the Expr, Field, Label, Name, and Variable types are neither modeled nor validated fully. These types are essentially strings at this time.

  2. The validation logic does not express the full nuances of PlusCal, especially as it relates to label placement.

    See section 3.7 of the PlusCal manual.

  3. Some of the fainess operations are not yet yet implemented.

    See section 4.6 of the PlusCal manual.

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