A compiler complies code! parts of compilers lexical analysis make stuff tokens — “identifying words” an example! if x == y then z = 1; else z = 2; if: keyword " “: white space x: identifier ==: relation … and so on parsing abstract syntax treeifying the tokens — “identifying sentences”. See parser. semantic analysis semantic analysis optimization (compilers) make the IR faster — “editing”. goals run faster use less memory generally, conserve resources tricky tricky! Can this be optimized to x=0? x = y * 0 Its tricky. y may not be numeric; y maybe float, then in which can nan * 0 = nan. code generation generate machine code — “translation.” Consider: register layout, etc. other stuff intermediate representation compliers typically translate between multiple intermediate languages. all but the first and last representations are called intermediate representations IRs are generally ordered in descending levels of abstraction digraph { rankdir=LR; graph [bgcolor=transparent]; node [fontcolor=white, color=white, shape=none]; edge [fontcolor=white, color=white]; ir1 [label="ir"] source -> ir -> "..." -> ir1 -> {assembly, ir1} } issues many pitfalls: your copmiler maybe slow may not be able to error nous inputs language design is important – determines what is ambiguous (hence what is easy / hard to compile) tradeoffs! in language design