Introduction

A more realistic title would be Language Implementation Techniques since compilers incorporate interpreters, although for very specialized languages, and interpreters incorporate compilers.

What is a compiler? A translator from one language to another. The target language is usually either at the ``same'' level or ``lower'' according to some fuzzy metric by which we classify languages.

What is an interpreter? A giver of meaning, for example, the hardware gives meaning to the bit patterns representing instructions or consider languages such as Basic, ML and Lisp.

Influences: architecture (CISC, RISC, microcoded), grammar (complexity), semantics (procedural, logic, functional, dataflow, rewrite, object-oriented, typeless, statically typed, dynamically typed).

Philosophical aspects of compilation: interpreter (meaning), translator (grammar), transformer (optimisation).

Task of compiler writing is to find a path through this jungle of ideas using the tools that have been created to assist in compiler writing over many years-program generators exist for each phase of compilation.

Examples will be given in C, Lisp, ML and M68000 assembler.

Classify kinds of compiler by the kind of output:

• pure machine code/native-rare, embedded systems

• augmented machine code (run-time libraries)-for example, C

• virtual machine code (tends to be CISC rather than RISC)-for example, ML, Scheme, GNU Lisp (byte-compile-file), Spitbol, Pascal-for interpretation

• symbolic assembler-Unix compilers, PSL, Spitbol (Minimal)

• relocatable binary-for later linking

• load and go (equivalent to a.out)-IBM FORTRAN and FLACC Algol68, fast enough for interaction as well as providing good debugging.

• source code, which offers better debugging that machine code-for example, Lisp, BASIC, SNOBOL/Spitbol

• on-the-fly compilation, either to VM or to augmented machine code; byte-codes can be interpreted by a program in a HLL or by microcode; example languages are Scheme, ML, Pascal.