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Pflow.xyz is an SDK for constructing petri-net smart contracts.

This article explores some features of the PflowDSL – which is an internal DSL to build models embedded in solidity code.

This is an excerpt from a demo model deployed to sepolia-optimism testnet. The above model contains every term that the language allows for, here’s a translation to petri-net terminology.

• cell() – [place] declares a memory location in the ‘state’ of the model
• func() – [transition] declares a transformation that mutates state
• arrow() – [arc]connectes cell() –> func() or func() –> cell
• guard() – [inhibitor arc] an arrow used as a ‘if/unless’ precondition

Some additional attributes of the language:

Declarative Style: Using the DSL is essentially describing the structure of the Petri net (places, transitions, arcs) rather than providing step-by-step instructions on how to build it.

• Functional Composition: The DSL uses functions like cell, func, arrow, and guard to define individual components and then connect them to form the complete net.
• Data-Centric: The core data structures are places and transitions, and the functions operate on and modify these structures.

Syntax:

• Function Calls as Building Blocks: The syntax of function calls in the DSL (cell(...), func(...)) visually resembles Lisp's s-expression syntax, where everything is enclosed in parentheses and the first element is typically the function name.
• Minimal Syntax: The DSL keeps the syntax quite minimal, focusing on the essential elements needed to define the Petri net.

Altogether, the Pflow SDK provides a way to enrich the syntax of your contract using another derived App-specific language.

Notice that in animation below -

The labels of the model can be used to visualize the state of the contract —also including a red/green coloring to indicate the ‘fireable-ness’ of the transition.

In conclusion

Pflow.xyz, with its internal PflowDSL, offers a novel and expressive approach to building Petri-net smart contracts. By enabling a declarative, functional, and data-centric construction of complex state machines, it enhances the clarity and maintainability of your Solidity code.

Learn more about how to make these models! Explore the solidity API: in the pflow.xyz docs. Or, view source code for the demo on sepolia-optimism testnet block explorer.