AST节点中的“ nosink”

Question

这来自this issue in the Perl 6 documentation，关于结肠对的区别对待； :a等效于a => True，而(:a:b)等于(a => True b => 1)，而:a:b或:a :b仅仅丢弃第二个；结肠对的行为根据其在第二或第一位置的不同而不同。 所以我看了QAST，它打印了这个：

  - QAST::Block(:cuid(2))  :in_stmt_mod<?> #!/usr/bin/env perl6\n\nuse v6;\n\nsay (:a:b);\n
      - QAST::Var(local __args__ :decl(param)) 
      - QAST::Stmts  #!/usr/bin/env perl6\n\nuse v6;\n\nsay (:a:b);\n
      - QAST::Op(call) 
        - QAST::Block(:cuid(1) :blocktype(declaration_static))  :outer<?> :in_stmt_mod<?> :code_object<?> :IN_DECL<mainline>
          - QAST::Stmts  #!/usr/bin/env perl6\n\nuse v6;\n\nsay (:a:b);\n
            - QAST::Var(lexical $¢ :decl(contvar)) 
            - QAST::Var(lexical $! :decl(contvar)) 
            - QAST::Var(lexical $/ :decl(contvar)) 
            - QAST::Var(lexical $_ :decl(contvar)) 
            - QAST::Var(lexical GLOBALish :decl(static)) 
            - QAST::Var(lexical EXPORT :decl(static)) 
            - QAST::Var(lexical $?PACKAGE :decl(static)) 
            - QAST::Var(lexical ::?PACKAGE :decl(static)) 
            - QAST::Var(lexical $=finish :decl(static)) 
            - QAST::Var(lexical $=pod :decl(static)) 
              [value]
                - 
            - QAST::Var(lexical !UNIT_MARKER :decl(static)) 
          - QAST::Stmts 
            - QAST::Op(bind) 
              - QAST::Var(local ctxsave :decl(var)) 
              - QAST::Var(contextual $*CTXSAVE) 
            - QAST::Op(unless) 
              - QAST::Op(isnull) 
                - QAST::Var(local ctxsave) 
              - QAST::Op(if) 
                - QAST::Op(can) 
                  - QAST::Var(local ctxsave) 
                  - QAST::SVal(ctxsave) 
                - QAST::Op(callmethod ctxsave) 
                  - QAST::Var(local ctxsave) 
          - QAST::Stmts 
            - QAST::WVal(Array) 
            - QAST::Stmts <sunk> ;\n\nsay (:a:b);\n
              - QAST::Stmt <sunk final> say (:a:b)
                - QAST::Want <sunk>
                  - QAST::Op(call &say) <sunk> :statement_id<2> say (:a:b)
                    - QAST::Stmts <wanted> (:a:b)
                      - QAST::Op(call &infix:<,>) 
                        - QAST::Op(callmethod new) <wanted> :a
                          - QAST::Var(lexical Pair) <wanted> :a
                          - QAST::Want <wanted>
                            - QAST::WVal(Str) 
                            - Ss
                            - QAST::SVal(a) 
                          - QAST::Op(hllbool) <wanted>
                            - QAST::IVal(1) 
                        - QAST::Op(callmethod new) <wanted nosink> :b
                          - QAST::Var(lexical Pair) <wanted> :b
                          - QAST::Want <wanted>
                            - QAST::WVal(Str) 
                            - Ss
                            - QAST::SVal(b) 
                          - QAST::Want <wanted>
                            - QAST::IVal(1) 
                  - v
                  - QAST::Op(p6sink) 
                    - QAST::Op(call &say) <sunk> :statement_id<2> say (:a:b)
                      - QAST::Stmts <wanted> (:a:b)
                        - QAST::Op(call &infix:<,>) 
                          - QAST::Op(callmethod new) <wanted> :a
                            - QAST::Var(lexical Pair) <wanted> :a
                            - QAST::Want <wanted>
                              - QAST::WVal(Str) 
                              - Ss
                              - QAST::SVal(a) 
                            - QAST::Op(hllbool) <wanted>
                              - QAST::IVal(1) 
                          - QAST::Op(callmethod new) <wanted nosink> :b
                            - QAST::Var(lexical Pair) <wanted> :b
                            - QAST::Want <wanted>
                              - QAST::WVal(Str) 
                              - Ss
                              - QAST::SVal(b) 
                            - QAST::Want <wanted>
                              - QAST::IVal(1) 
            - QAST::WVal(Nil) 

主要区别在于，第一个冒号对是- QAST::Op(callmethod new) <wanted> :a，而第二个是- QAST::Op(callmethod new) <wanted nosink> :b，请注意nosink。我想最重要的部分是隐式运算符的调用位置。此运算符下沉第一个元素。但是我想知道为什么下沉的效果是使Pair中的值等于True，而没有下沉的结果使其等于1。那是故意的吗？一些副作用或我无法真正理解的东西？以上都不是吗？