Title: Concrete syntax matters, actually

Abstract: Too many programming languages researchers dismiss concrete syntax as an afterthought: arbitrary, superficial, or distracting from matters of “actual” (semantic) importance. This received view ignores a critical factor: the human at the computer. Concrete syntax defines the principal interface through which programmers interact with the vast majority of programming languages. Moreover, this interface is hardly decoupled from semantics; even trivial-seeming differences in keywords, sigils, and indentation can affect how programmers utilize and reason about language behavior. Using examples from asynchronous control flow, gradual subtyping, first-class functions, and more, I will make a case for the importance of concrete syntax, why language designers often overlook it, and what this implies for those of us who care about the usability of abstractions. Finally, I will describe some preliminary work evaluating the role of lexical ambiguity in programmer comprehension of type system features.