When writing functional code that composes multiple recursive functions that operate on a datastrcuture, we often incur a lot of computational overhead allocating memory, only to later read, use, and discard this information.
This can be alleviated using fusion, a technique that combines these multiple recursive datastructure traversals into one.
This thesis explores shortcut fusion using (Co)Church encodings based on the work of Harper (2011), focusing on two questions: What is needed to reliably achieve fusion in Haskell, and the correctness of these transformations through a formalization in Agda.

The first contribution replicates and extends Harper's (Co)Church encodings in Haskell, uncovering optimizer weaknesses and providing practical insights for achieving fusion within Haskell.
The second contribution formalizes these encodings in Agda, leveraging parametricity and the category theory described by Harper.
The formalization proves the equivalence of these encoded functions to the unencoded ones, showing that the encodings are in fact isomorphisms, as long as parametricity (Wadler, 1989) is assumed.

These findings highlight the effectiveness and correctness of shortcut fusion techniques and show the promise of shortcut fusion: Reduce the computational overhead associated with functional programming while retaining its nice, compositional properties.

Raccoon Serious Games develops and hosts educational activities such as escape room events and serious games. They create both physically- and digitally-based escape rooms across many different scales. These events consist of a variety of puzzles and tasks the player(s) have to solve in order to finish or `escape' the event. For their digitally hosted events, the Massive Online Reactive Serious Escape 2.0 (MORSE) system is used for creation and configuration of the needed underlying rules of the event. The system uses the `If This Then That' (IFTTT) principle for creating rules, where a trigger activated by the player/game can initiate a check about the state of the game which then results in an action by the game. In MORSE the user (usually the game host) can choose from the multiple types of triggers, conditions, and actions to create logical statements in the IFTTT format. These statements together form the rules of the game. This system, although a good improvement over the previously hard-coded procedure, has proven unintuitive to program for most of the employees at Raccoon Serious Games. The IFTTT format used is unwieldy to work with for the designers, who have little to no programming background. Furthermore this existing system provides no overview of the rules system making it challenging to visualise the whole game and its dynamics. To solve the unintuitive nature of MORSE, our team designed and developed Feather: A graph-based visual editing tool that is integrated into MORSE. It can generate rule and ruleset logic needed for the client's escape events. It uses visual components and presents the user with a graph of the whole game during the design process. The editor can be used together with all other, earlier existing, features for creating rulesets of the MORSE system. This tool has most of the functionality the current system has, with the possibility of easily extending it with new components. The product was built as an addition to MORSE over the course of 10 weeks. In the initial part of the project a thorough research was performed on the needs of the client as well as useful resources or libraries and design practices for domain specific visual languages. The second part of the project was devoted to the design and implementation of the tool. Throughout the duration of the project a number of user tests were conducted with the employees at Raccoon Serious Games to assess the understanding and usability of the product.