/usr/local/CPAN/Perl6-Pugs/02Architecture.pod

Pugs Apocryphon 2: Architecture

- Reason of Pugs
 - make Perl 6 programs run
 - Explain the Perl6 parts more; assume no Haskell
- What is the difference between how Perl 5 and Perl 6 runs programs?
 - Separate parse/compilation/runtime phase
- What does the Parser do?
  - match the source with regexes defined in Perl 6 Grammar
  - which is just a set of regexes to match language parts
  - does not check "1=2" or any other compile time errors
  - either parses into syntax tree, or report syntax error
  - the syntax tree may be completely bogus
- What does the Compiler do?
 - decide the "meaning" of syntax trees
 - translate various special forms into the same underlying operations
- What is "PIL"?
 - Pugs Intermediate Language
 - very few node types
 - Verbs: Apply (function call), Assign, Bind (give new name)
 - Nouns: Literals, Expression
 - expression: inline assembly, variables, thunks, code
 - (explain the PIL forms more, with examples)
- Why "PIL"?
 - doesn't care how program was "written", only what it "means"
 - Don't program in PIL because it's very verbose
 - But it represents anything Perl programs can do
 - It only has five operations (also known as "nodes")
- The PIL evaluator
 - At this moment is the reference implementation of how Perl 6 works
 - Will eventually be written entirely in Perl 6
 - Will be one of the many backends in the end, among Parrot, Perl 5, and others
- The Code generator
 - translates PIL operations into target languages
 - the underlying language still have to provide a runtime and builtin functions