\chapter{Introduction}

\CFA{}\footnote{Pronounced ``C-for-all'', and written \CFA{} or \CFL{}.} is an evolutionary modernization of the C programming language. 
\CFA{} both fixes existing design problems and adds multiple new features to C, including name overloading, user-defined operators, parametric-polymorphic routines, and type constructors and destructors, among others. 
The new features make \CFA{} more powerful and expressive than C, but impose a compile-time cost, particularly in the expression resolver, which must evaluate the typing rules of a significantly more complex type-system.

This thesis is focused on making \CFA{} a more powerful and expressive language, both by adding new features to the \CFA{} type system and ensuring that both added and existing features can be efficiently implemented in \CFACC{}, the \CFA{} reference compiler. 
Particular contributions of this work include design and implementation of 
parametric-polymorphic (``generic'') types in a manner compatible with the existing polymorphism design of \CFA{} (Chapter~\ref{generic-chap}), a type environment data structure based on a novel variant of the union-find algorithm (Chapter~\ref{env-chap}), and a new expression resolution algorithm designed to quickly locate the optimal declarations for a \CFA{} declaration (Chapter~\ref{resolution-chap}). 
This expression resolution algorithm was designed with the aid of a purpose-built prototype system which encapsulates the essential aspects of the \CFA{} type system without incurring the technical debt of the existing system or the friction-inducing necessity of maintaining a working compiler; the goal of this prototype system was to discover effective heuristics to avoid performing unnecessary work in the process of locating the optimal \CFA{} expression resolution.

Though the direction and validation of this work was fairly narrowly focused on the \CFA{} programming language, the tools used and results obtained should be of interest to a wider compiler and programming language design community. 
In particular, with the addition of \emph{concepts} in \CCtwenty{}, conforming \CC{} compilers must support a model of type assertions very similar to that in \CFA{}, and the algorithmic techniques used in the expression resolution algorithm presented here may prove useful. 
Type environments are also widely modelled in compiler implementations, particularly of functional languages, though also increasingly commonly in other languages (such as Rust) which also perform type inference; the type environment presented here may be useful to those language implementers.
