digraph Compiler {
    Source          -> Lexer
    Lexer           -> Tokens
    Tokens          -> Semantics
    Semantics       -> Parser
    Parser          -> ExpressionTree
    ExpressionTree  -> Optimizer -> ExpressionTree [style=dotted]
    ExpressionTree  -> Emitter
    Emitter         -> Output

    Source          [shape=box]
    Tokens          [shape=box]
    ExpressionTree  [shape=box]
    Output          [shape=box]
}