Re: New in todo.txt

[Krux02]

To start with a practical example, I would like to talk about, how I would 
pattern match the NimNode types, mostly because they are types I would care 
about. The syntax should be almost identical to the construction, just it 
should work in reverse. Here is an example of how I could imagine it:
    
    
    import macros
    
    proc foobar(arg: NimNode, id: int): void =
      echo arg.repr
    
    macro myMacro(arg:untyped): untyped =
      for section in arg:
        case section # pattern matching is always the whole object, not just 
the kind
        of nnkCall.newTree(ident"variantA", `stmtList`):
          foobar(stmtList, 0)
        of nnkCall.newTree(ident"variontB", `stmtList`):
          foobar(stmtList, 1)
        of nnkCall.newTree(ident"variantC",  
nnkStmtList.newTree(nnkCall.newTree(ident"subVariantA", `stmtList`))):
          foobar(stmtList, 2)
        of nnkCall.newTree(ident"variantC",  
nnkStmtList.newTree(nnkCall.newTree(ident"subVariantB", `stmtList`))):
          foobar(stmtList, 3)
    
    Mymacro:
      variantA:
        a += 1
        b += 2
      
      variantB:
        a += 4
        b += 8
      
      variantC:
        subVariantA:
          a += 8
          b += 19
      
      variantC:
        subVariantB:
          a += 20
          b += 30
    

Full input ast:
    
    
    StmtList
      Call
        Ident !"variantA"
        StmtList
          Infix
            Ident !"+="
            Ident !"a"
            IntLit 1
          Infix
            Ident !"+="
            Ident !"b"
            IntLit 2
      Call
        Ident !"variantB"
        StmtList
          Infix
            Ident !"+="
            Ident !"a"
            IntLit 4
          Infix
            Ident !"+="
            Ident !"b"
            IntLit 8
      Call
        Ident !"variantC"
        StmtList
          Call
            Ident !"subVariantA"
            StmtList
              Infix
                Ident !"+="
                Ident !"a"
                IntLit 8
              Infix
                Ident !"+="
                Ident !"b"
                IntLit 19
      Call
        Ident !"variantC"
        StmtList
          Call
            Ident !"subVariantB"
            StmtList
              Infix
                Ident !"+="
                Ident !"a"
                IntLit 20
              Infix
                Ident !"+="
                Ident !"b"
                IntLit 30
    

I have to admit thet `newTree` is not the best name to extract trees, but that 
is the way I construct them, and that is the only syntax that works reliably 
with every node kind.