It is time for Cone to get a proper module system. This design space is complex and rife with historical missteps. In order to distill the topography of the landscape and clarify the key requirements, I felt it necessary to begin the journey with cross-language research and contemplation. I wound up pursuing three rabbit-chasing adventures in module wonderland: What do programmers want from modularity? You can read about this adventure in my earlier post on modularity, which captures what we want from modularity, and summarizes how the three modularity capabilities are surfaced across different layers of programming language features (and program decomposition).
Cone’s module system has been on my mind of late. The best design for modules is neither easy or obvious, as evidenced by how much modules vary from one language to the next. To guide my approach for Cone, I went back to basics: What is the role (and benefit) that modularity plays in programming (languages)? What role do modules play within this larger picture. This post synthesizes my findings.
I have long enjoyed the convenience of the “dot” dispatch syntax: instance.log("Ethereal cognistrands do not support quantum entanglement") The magic of Universal Function Call Syntax makes this sugar for a function call: log(instance, "Ethereal cognistrands do not support quantum entanglement") The broad popularity of method dispatch is driven by these benefits: Ad hoc polymorphism. When used in conjunction with method overloading, we can reuse the same easier-to-remember semantic names across multiple types and parameter configurations, with minimal-to-no ambiguity on which implementation to use.
Note: This is a heavily revised version of an earlier post The Cone compiler performs a data flow analysis pass after name resolution and type checking. Given that this sort of analysis is rarely covered by compiler literature, I thought it might be useful to jot down some thoughts about its purpose and intriguing mechanics. Trigger Warning: This blog post is highly technical and brief. It reads more like an organizing outline for a design spec than a typical essay-oriented post.
The previous Lifecycle of a Reference post illuminates the working relationship between references and regions. It explains how a reference’s region annotations are programmer-definable struct-like types, which can specify an allocated object’s region state using fields, and region-based operations on an object (e.g., allocate and free) using methods. This, however, leaves out an important part of the story about region definitions: their global state and global runtime logic. Holistically, a Cone region is fully defined by an importable module, within which lies:
Over two and half years ago, I described something I called Gradual Memory Management. Inspired by Rust and Pony, my paper proposed that it is feasible and desirable for a systems programming language to allow programs to exploit multiple memory management and permission strategies. Without putting memory and data race safety at risk, doing so would facilitate significant improvements to throughput and latency, even in multi-threaded architectures. It is easy to propose wild ideas in words.
I seem to be on a roll with syntactic concerns lately, which is not where I typically spend most of my time. Today’s issue is, at least, more unusual than stylistic preferences regarding semicolons and significant indentation. This post explores the issues that arise when teaching the compiler to be agnostic as to whether it is parsing a value expression or a type expression. A value expression computes some typed value when evaluated:
The last post focused narrowly on evaluating various techniques for semi-colon inference, thereby enabling a program to successfully compile even when the programmer omits statement-ending semicolons. This post broadens this theme, looding at how the compiler can take advantage of significant indentation when handling block inference and multi-line string literals. I wander into this topic knowing that for many programmers, compiler support for significant indentation is troubling and uncomfortable. They prefer the explicit clarity of required semi-colons to end statements and curly braces to delimit blocks.
The last two posts introduced the fundamental elements underlying Cone’s type system. They also distinguished between nominal vs. structural type equivalence. However, they were largely silent about subtyping relationships between types. Given how important subtyping is to Cone’s type versatility, I thought it might also be valuable to offer a detailed treatment of these mechanisms. My approach will be practical, rather than formal (alas! no subsumptions nor lattices), distilling lessons learned from implementing a rich, but type-safe collection of subtyping mechanisms.