Dotty tutorial

Dotty internals: the frontend

Generating trees and symbols and typing them

The compiler pipeline

Fundamental data structures

• The compiler represents code using trees
• To ensure type-safety, we attach types to trees
• A type might refer to an identifier defined in a tree or in the classpath, to each valid identifier corresponds a symbol looked up in the symbol table for the current scope
• Each phase of the compiler pipeline simplifies the trees and types until they can be easily expressed using Java bytecode
• All of these data structures are immutable (or look immutable but use caching under the hood)

Parser: From source file to Untyped Tree

obj.fun(5)

obj.fun(5)

Apply(Select(Ident("obj"), "fun"), Literal(5))

Dotty internals: the middle-end

Simplifing types and trees with successive transformations

Traditional phase design

1 phase = 1 full traversal

Mini-phase design

N fused mini-phases = 1 full traversal