Compiler techniques are effective and efficient in processing textual programming languages. These techniques can be adapted to recognition and processing of two-dimensional languages (diagrams). Already, grammars and parsers have been used in a variety of diagram-recognition and diagram-processing tasks. Here we explore the use of two other compiler techniques in pattern recognition systems. The first is compiler-style use of trees and tree transformation. The second is a multi-pass control structure, with a clear separation between layout, lexical, syntactic, and semantic analysis. Our proposal is illustrated on a case study involving recognition of hand-drawn mathematics notation.