Thin Io-facing facade over the C lexer (IoLexer) and the C recursive- descent parser (IoMessage_parser). Exposes three Io-visible entry points — tokensForString, messageForString, messageForString2 — that run a source string through IoLexer_lex, surface any errorToken as an Io "compile error" Exception, and either hand back a list of token description objects or the root IoMessage of the parsed chain. The Compiler proto itself is just a slot-holder; there is no compiled bytecode representation in Io, so "compiling" means producing a message tree.
Creates the Compiler proto (a plain IoObject, not a tagged primitive) and installs the Io-visible method table. Called once during IoState init. A type slot is stamped so Compiler objects identify themselves the way the rest of the VM expects.