petalc/dlang.md

Implementing the compiler in D

How would we implement the compiler in D?

• Use Bison as the compiler generator. Recent Bison supports D.
  • This requires me to write AST creation stuff manually, which kind of sucks.
  • But I don’t have to write an AST-to-semantic copier, which is nice.
• Hand-written lexer?
  • Can autogenerate the detect-literal portion of it using a prefix tree.
• Use LLVM-C API instead of writing to a file.
  • This lets me keep a local variable basic block open, which means fewer separate visitors.
• Use RTTI-switch visitor instead of indirection visitor.
• Use reflection to implement visitChildren.
• Use reflection to implement rewrite visitor.
• Use make instead of dub to build, because we really don’t need dub.

String interpolation

The hand-written lexer makes string interpolation easier:

"Hello $name! You are ${person:years} old!"

becomes:

INTERP_START
STRING("Hello ")
IDENT("name")
STRING("! You are ")
IDENT("person")
CHILD
IDENT("years")
STRING(" old!")
INTERP_END

Because the hand-written lexer can do a lot more. Then I have productions like:

string: STRING | INTERP_START exp* INTERP_END;