Synopsis

• Program is just a stream of characters
• Lexer forms “words” (called tokens) from characters and can already detect lexical errors.
• Parser checks if token stream adheres to concrete syntax. If yes, it builds the AST, if not, it reports errors.
• However, not all syntactically correct programs are valid C programs.
• They can violate static semantics: types don’t match.
• Analyzing static semantics (“semantic analysis”) can detect such errors and discard erroneous programs.
• As a side effect, it elaborates types which we need later on for code generation.
• Language is statically type-safe if well-typed programs don’t get stuck.
• Discuss examples of C programs that are well-typed but get stuck and discuss how Java solves these problems.
• Introduce type system for C0 (Section 6.6): relation of a type environment, an expression, and its type.
• Define typing rules inductively over the syntax.

Sections Covered