Let's make a programming language. Functions—Key points

In our latest episode, Yuri Minaev, a seasoned C++ developer and architect at PVS-Studio, guides us through the implementation of functions in our toy programming language. Using C++, Yuri explains how functions establish their own scope, distinct from the global scope where variables reside. Inside a function, names are not visible outside, while names from parent scopes remain accessible.

Yuri also introduces compound statements, which can create nested scopes. To manage the symbol table and resolve names, the semantic analyzer employs a symbol table that links names with declarators and their respective scopes. Two lookup methods are utilized: an unscoped lookup searches the current scope and ascends through parent scopes until it finds the name, while a scoped lookup checks only the specified scope, preventing duplicate names within the same scope.

The parsing of functions involves the fn keyword, a name, parameters, an optional return type, and a compound statement constituting the body. Parameters consist of a type and a unique name. Parsing occurs in two stages: the function's declaration is parsed and registered in the symbol table before processing its body. This enables functions to reference themselves recursively.

The semantic analyzer ascertains a function's return type from its return statements when no type is specified. It also verifies that return expressions are compatible with the function's return type and inserts implicit casts when necessary. A function devoid of return statements receives the void type. Incompatible return types render the function invalid.

The episode concludes with Yuri acknowledging the completion of functions and introducing the evaluator as the subsequent topic. He invites viewers to follow for more talks and sign up for upcoming webinars, such as "Let's make a programming language. Evaluator." He concludes by expressing hope to see his audience at the webinars and encouraging those interested in learning more about the PVS-Studio analyzer to visit their website.