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https://github.com/dhil/phd-dissertation

A summary of my activities during the past four years
https://github.com/dhil/phd-dissertation

abstract-machines algebraic-effects computational-effects continuation-passing-style continuations control-effects effect-handler-oriented-programming effect-handlers expressiveness expressivity functional-programming phd-dissertation phd-thesis research unix

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A summary of my activities during the past four years

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# Foundations for programming and implementing effect handlers



A copy of my dissertation can be [downloaded via my

website](https://dhil.net/research/papers/thesis.pdf).



----



Submitted on May 30, 2021. Examined on August 13, 2021.



The board of examiners were



* [Andrew Kennedy](https://github.com/andrewjkennedy) (Facebook London)

* [Edwin Brady](https://www.type-driven.org.uk/edwinb/) (University of St Andrews)

* [Ohad Kammar](http://denotational.co.uk/) (The University of Edinburgh)

* [Stephen Gilmore](https://homepages.inf.ed.ac.uk/stg/) (The University of Edinburgh)



## Thesis structure



The dissertation is structured as follows.



### Introduction



 * Chapter 1 puts forth an argument for why effect handlers

   matter. Following this argument it provides a basic introduction to

   several different approaches to effectful programming through the

   lens of the state effect. In addition, it also declares the scope

   and contributions of the dissertation, and discusses some related

   work.



### Programming



 * Chapter 2 illustrates effect handler oriented programming by

   example by implementing a small operating system dubbed Tiny UNIX,

   which captures some essential traits of Ritchie and Thompson's

   UNIX. The implementation starts with a basic notion of file i/o,

   and then, it evolves into a feature-rich operating system with full

   file i/o, multiple user environments, multi-tasking, and more, by

   composing ever more effect handlers.



 * Chapter 3 introduces a polymorphic fine-grain call-by-value core

   calculus, λb, which makes key use of Rémy-style row

   polymorphism to implement polymorphic variants, structural records,

   and a structural effect system. The calculus distils the essence of

   the core of the Links programming language. The chapter also

   presents three extensions of λb, which are λh

   that adds deep handlers, λ† that adds shallow handlers,

   and λ‡ that adds parameterised handlers.



### Implementation



 * Chapter 4 develops a higher-order continuation passing style

   translation for effect handlers through a series of step-wise

   refinements of an initial standard continuation passing style

   translation for λb. Each refinement slightly modifies

   the notion of continuation employed by the translation. The

   development ultimately leads to the key invention of generalised

   continuation, which is used to give a continuation passing style

   semantics to deep, shallow, and parameterised handlers.



 * Chapter 5 demonstrates an application of generalised continuations

   to abstract machine as we plug generalised continuations into

   Felleisen and Friedman's CEK machine to obtain an adequate abstract

   runtime with simultaneous support for deep, shallow, and

   parameterised handlers.



### Expressiveness



 * Chapter 6 shows that deep, shallow, and parameterised notions of

   handlers can simulate one another up to specific notions of

   administrative reduction.



 * Chapter 7 studies the fundamental efficiency of effect handlers. In

   this chapter, we show that effect handlers enable an asymptotic

   improvement in runtime complexity for a certain class of

   functions. Specifically, we consider the *generic count* problem

   using a pure PCF-like base language λb→ (a

   simply typed variation of λb) and its extension with

   effect handlers λh→.  We show that

   λh→ admits an asymptotically more efficient

   implementation of generic count than any λb→

   implementation.



### Conclusions

  * Chapter 8 concludes and discusses future work.



### Appendices



 * Appendix A contains a literature survey of continuations and

   first-class control. I classify continuations according to their

   operational behaviour and provide an overview of the various

   first-class sequential control operators that appear in the

   literature. The application spectrum of continuations is discussed

   as well as implementation strategies for first-class control.

 * Appendix B contains a proof that shows the `Get-get` equation for

   state is redundant.

 * Appendix C contains the proof details and gadgetry for the

   complexity of the effectful generic count program.

 * Appendix D provides a sample implementation of the Berger count

   program and discusses it in more detail.



## Building



To build the dissertation you need the [Informatics thesis LaTeX

class](https://github.com/dhil/inf-thesis-latex-cls) with the

University of Edinburgh crests. Invoking `make` on the command line

ought to produce a PDF copy of the dissertation named `thesis.pdf`,

e.g.



```shell

$ make

```



## Timeline



I submitted my thesis on May 30, 2021. It was examined on August 13,

2021, where I received pass with minor corrections. The revised thesis

was submitted on December 22, 2021. It was approved on March

14, 2022. The final revision was submitted on March 23, 2022. I

received my PhD award letter on March 24, 2022. My graduation 

ceremony took place in McEwan Hall on July 11, 2022.