\section*{Components}

\begin{frame}
  \frametitle{Towards Attributed Trees as Components (1)}
  
  \begin{center}
  \begin{tikzpicture}
  [ nd/.style={circle, minimum size=9mm, very thick, draw=blue!50!black!50, top color=white, bottom color=blue!50!black!20,font=\scriptsize}
  , tr/.style={isosceles triangle,rotate=90, minimum size=12mm, very thick, draw=blue!50!black!50, top color=white, bottom color=blue!50!black!20,font=\footnotesize}
  , attr/.style={rectangle, minimum size=4mm, node distance=6mm, very thick, draw=black!50, top color=white, bottom color=black!20,font=\scriptsize}
  , inh/.style={attr}
  , syn/.style={attr}
  , leftfirst/.style={xshift=-4mm}
  , rightfirst/.style={xshift=4mm}
  , arr/.style={->,dashed, very thick}
  ]
  \node[nd](n1){|let|}
    [sibling distance=35mm, level distance=12mm]
    child {
      node[nd](n2){|cons|}
      [sibling distance=25mm]
        child {
          node[nd](n4){|decl|}
            child {
              node[nd](n5){|val|}
            }
        }
        child {
          [sibling distance=32mm]
          node[tr, xshift=-3mm](n6){|Decls|}
        }
    }
    child {
      [sibling distance=20mm]
      node[tr, xshift=-3mm](n3){|Expr|}
    };
  \node[right of=n3,xshift=-4mm](nx){};
  \begin{pgfonlayer}{background}
  \node[rectangle,fit=(n1)(nx)(n5), draw=black!50, fill=white]{};
  \end{pgfonlayer}
  
  \node[above of=n1,xshift=-20mm,yshift=-4mm, draw=black, fill=white, font=\scriptsize](i1){
    \begin{tabular}{l}
    |visit gather| \\
    |syn  gathEnv| \\
    \end{tabular}
  };
  
  \node[above of=n1,xshift=17mm,yshift=0mm, draw=black, fill=white, font=\scriptsize](i2){
    \begin{tabular}{l}
    |visit distribute| \\
    |inh finEnv| \\
    |syn errs|
    \end{tabular}
  };
  \pause
  \node[nd, above of=n1, xshift=-60mm, yshift=10mm](n20){|node|}
    child {
      node(target){};
    }
    child {
      node{};
    };
  \draw[-](n20) to (n1);
  \draw[-](n20) to (target);
  \pause
  \node[below of=target, xshift=20mm]{\scriptsize{
    \texths
    \begin{code}
    sem :: RealTree
      loc.c = ...
      child comp :: Comp = loc.c
      comp.finEnv = []
    \end{code}
  }};
  \end{tikzpicture}
  \end{center}
\end{frame}

\begin{frame}
  \frametitle{Show stoppers}
  
  \begin{enumerate}
  \item Verbose AST
    \begin{itemize}
    \item Expressions, declarations: too fine grained
    \item Essence of name analysis: binding sites, use sites, scoping
    \end{itemize}
  \item Interfacing only with root insufficient
    \begin{itemize}
    \item Access to the values found for identifiers
    \item Access to the error messages at one particular node
    \end{itemize}
  \item Extend a component?
    \begin{itemize}
    \item Mismatch between offered and needed functionality
    \item Opening up the component, without affecting the original
    \item Overriding attributes, adding new attributes
    \end{itemize}
  \item Intuitiveness and predictability of code?
    \begin{itemize}
    \item Delegation of work: finished when results are needed?
    \item Functional code (side effect free/order independent)
    \end{itemize}
  \end{enumerate}
\end{frame}


\section*{More abstract AST}

\begin{frame}
  \frametitle{Coarser AST}
  
  \begin{tikzpicture}
    [ nd/.style={circle, minimum size=9mm, very thick, draw=blue!50!black!50, top color=white, bottom color=blue!50!black!20,font=\scriptsize}
    , nd2/.style={circle, minimum size=9mm, very thick, draw=red!50!black!50, top color=white, bottom color=red!50!black!20,font=\scriptsize}
    , attr/.style={rectangle, minimum size=4mm, node distance=6mm, very thick, draw=black!50, top color=white, bottom color=black!20,font=\scriptsize}
    , inh/.style={attr}
    , syn/.style={attr}
    , leftfirst/.style={xshift=-4mm}
    , rightfirst/.style={xshift=4mm}
    , arr/.style={->,dashed, very thick}
    ]
    \node[nd](n1){|let|}
      [sibling distance=60mm, level distance=12mm]
      child {
        node[nd](n2){|cons|}
        [sibling distance=32mm]
          child {
            node[nd](n4){|x=|}
              child {
                node[nd](n5){|val|}
              }
          }
          child {
            [sibling distance=32mm]
            node[nd](n6){|cons|}
              child {
                node[nd](n7){|f=|}
                  child {
                    node[nd](n8){|\x|}
                      child {
                        node[nd](n9){|x|}
                      }
                  }
              }
              child {
                node[nd](n10){|nil|}
              }
          }
      }
      child {
        [sibling distance=20mm]
        node[nd](n3){|app|}
          child {
            node[nd](n11){|f|}
          }
          child {
            node[nd](n12){|x|}
          }
      };
  \pause
  \node[nd2,above of=n1](r1){|sc|}
    [level distance=12mm]
    child {
      node[nd2](r2){|split|}
        [sibling distance=50mm]
        child {
          node[nd2](r3){|split|}
            [sibling distance=30mm]
            child {
              node[nd2](r4){|def x|}
            }
            child {
              node[nd2](r5){|split|}
                child {
                  node[nd2](r6){|def f|}
                }
                child {
                  node[nd2](r7){|sc|}
                    child {
                      node[nd2](r8){|split|}
                        child {
                          node[nd2](r12){|def x|}
                        }
                        child {
                          node[nd2](r13){|use x|}
                        }
                    }
                }
            }
        }
        child {
          node[nd2](r9){|split|}
            [sibling distance=25mm]
            child {
              node[nd2](r10){|use f|}
            }
            child {
              node[nd2](r11){|use x|}
            }
        }
    };
  \end{tikzpicture}
\end{frame}

\begin{frame}
  \frametitle{Coarser AST}

  \begin{center}
  \begin{tikzpicture}
    [ nd/.style={circle, minimum size=9mm, very thick, draw=blue!50!black!50, top color=white, bottom color=blue!50!black!20,font=\scriptsize}
    , nd2/.style={circle, minimum size=9mm, very thick, draw=red!50!black!50, top color=white, bottom color=red!50!black!20,font=\scriptsize}
    , attr/.style={rectangle, minimum size=4mm, node distance=6mm, very thick, draw=black!50, top color=white, bottom color=black!20,font=\scriptsize}
    , inh/.style={attr}
    , syn/.style={attr}
    , leftfirst/.style={xshift=-4mm}
    , rightfirst/.style={xshift=4mm}
    , arr/.style={->,dashed, very thick}
    ]
  \node[nd2](r1){|sc|}
    child {
      node[nd2](r2){|split|}
        [sibling distance=30mm]
        child {
          node[nd2](r3){|def x|}
        }
        child {
          node[nd2](r4){|use x|}
        }
    };
  \end{tikzpicture}
  \end{center}
\end{frame}

\begin{frame}
  \frametitle{More Abstract Code}
  
  \scriptsize{
  \begin{code}
  itf Name alpha   ^^ visit gather      ^^ syn  gathEnv huse {++} {[]} :: [(String, alpha)]
                   ^^ visit distribute  ^^ inh  finEnv  :: [(String, alpha)]
                                        ^^ syn  errors  huse {++} {[]}:: [String]

  sem_Name_Scope b =
    sem :: Name alpha
      child body :: Name alpha = b
      body.finEnv = (lhs.finEnv \\ (map fst body.gathEnv)) ++ body.gathEnv
  
  sem_Name_Split l r =
    sem :: Name alpha
      child left   :: Name alpha = l
      child right  :: Name alpha = r
  
  sem_Name_Def x v =
    sem :: Name alpha
      lhs.gathEnv  = [(x,v)]
      lhs.errors   =  if length (filter ((== x) . fst) lhs.finEnv) > 1
                      then ["dup: " ++ x] else []
  
  sem_Name_Use x =
    sem :: Name alpha
      loc.mbVal   = lookup x lhs.finEnv
      lhs.errors  = if isNothing loc.mbVal then ["missing: " ++ x] else []
      loc.val     = maybe undefined id loc.mbVal -- how to access this??
  \end{code}}
\end{frame}

\begin{frame}
  \frametitle{Instantiation of the component}

\small{
\begin{code}
itf Expr  syn nmTree :: T_Name st Ty

sem_Expr_Lam x b =
  sem :: Expr
    child body :: Expr = b
    loc.ty = ...
    lhs.nmTree  = sem_Name_Scope
                $ sem_Name_Split (sem_Name_Def x loc.ty)
                $ body.nmTree

sem_Expr_Var x =
  sem :: Expr
    lhs.nmTree = sem_Name_Use x

sem_Root_Root b =
  sem :: Root
    child body :: Expr = b
    child name :: Name Ty = body.nmTree
    lhs.errors = name.errors
\end{code}}
\end{frame}


\section*{Interface to Subtrees}

\begin{frame}
  \frametitle{Towards Attributed Trees as Components (2)}
  
  \begin{center}
  \begin{tikzpicture}
    [ nd/.style={circle, minimum size=9mm, very thick, draw=blue!50!black!50, top color=white, bottom color=blue!50!black!20,font=\scriptsize}
    , nd2/.style={circle, minimum size=9mm, very thick, draw=red!50!black!50, top color=white, bottom color=red!50!black!20,font=\scriptsize}
    , nd3/.style={circle, minimum size=6mm, very thick, draw=green!50!black!50, top color=white, bottom color=green!50!black!20,font=\scriptsize}
    , attr/.style={rectangle, minimum size=2mm, node distance=4mm, very thick, draw=black!50, top color=white, bottom color=black!20,font=\scriptsize}
    , inh/.style={attr}
    , syn/.style={attr}
    , leftfirst/.style={xshift=-4mm}
    , rightfirst/.style={xshift=4mm}
    , arr/.style={->,dashed, very thick}
    ]
  \node[nd2](r1){|sc|}
    child {
      node[nd2](r2){|split|}
        [sibling distance=30mm]
        child {
          node[nd2](r3){|def x|}
        }
        child {
          node[nd2](r4){|use x|}
        }
    };
  \begin{pgfonlayer}{background}
  \node[rectangle,fit=(r1)(r2)(r3)(r4), draw=black!50, fill=white]{};
  \end{pgfonlayer}
  
  \node[nd3,left of=r3,xshift=5mm](r5){};
  \node[nd3,right of=r4,xshift=-5mm](r6){};
  
  \node[above of=r1,yshift=4mm, draw=black, fill=white, font=\scriptsize](i1){
    \texths
    \begin{code}
    itf Name
    visit gather
      syn  gathEnv
    visit distribute
      inh  finEnv
    \end{code}
  };
  \node[left of=r5,xshift=-2mm, draw=black, fill=white, font=\scriptsize](i2) {
    \texths
    \begin{code}
    itf NameDef
    visit supply
      syn  nm
      syn  value
    visit outcome
      inh  errors
    \end{code}
  };
  \node[right of=r6,xshift=2mm, draw=black, fill=white, font=\scriptsize](i2) {
    \texths
    \begin{code}
    itf NameUse
    visit supply
      syn  nm
    visit outcome
      inh  value
      inh  errors
    \end{code}
  };
  \end{tikzpicture}
  \end{center}
\end{frame}

\begin{frame}
  \frametitle{Instantiation and Exchange}
  
  \begin{center}
  \begin{tikzpicture}
    [ nd/.style={circle, minimum size=9mm, very thick, draw=blue!50!black!50, top color=white, bottom color=blue!50!black!20,font=\scriptsize}
    , nd2/.style={circle, minimum size=9mm, very thick, draw=red!50!black!50, top color=white, bottom color=red!50!black!20,font=\scriptsize}
    , nd3/.style={circle, minimum size=6mm, very thick, draw=green!50!black!50, top color=white, bottom color=green!50!black!20,font=\scriptsize}
    , attr/.style={rectangle, minimum size=4mm, node distance=6mm, very thick, draw=black!50, top color=white, bottom color=black!20,font=\scriptsize}
    , inh/.style={attr}
    , syn/.style={attr}
    , leftfirst/.style={xshift=-4mm}
    , rightfirst/.style={xshift=4mm}
    , arr/.style={->,dashed, very thick}
    ]
  \node[nd](n1){|root|}
    [sibling distance=50mm]
    child {
      node[nd](n2){|app|}
        [sibling distance=10mm, level distance=25mm]
        child {
          node{}
        }
        child {
          node[nd](n3){|var|}
        }
    }
    child {
      node[nd2](n7){|sc|}
        [level distance=10mm]
        child {
          node[nd2](n4){|split|}
            [sibling distance=10mm]
            child {
              node[nd2](n5){|use|}
            }
            child {
              node{}
            }
      }
    };
    \pause
    \node[nd3, right of=n3, xshift=-5mm](n6){};
    \draw[-](n6) to (n5);
    \node[attr,below of=n6](a4){};
    \node[attr,above of=n6](a3){};
    \node[attr,right of=a3](a5){};
    \node[above of=a5,xshift=5mm,yshift=-5mm]{|<- value,errors|};
    \node[right of=a4]{|nm ->|};
  \end{tikzpicture}
  \end{center}
\end{frame}

\begin{frame}
  \frametitle{Nested AG Code}
  
  \scriptsize{
  \begin{code}
   itf NameUse alpha  visit supply   syn  nm      :: String
                      visit outcome  inh  value   :: alpha
                                     inh  errors  :: [String]
  
  sem_Name_Use extTree =
    sem :: Name alpha
      child ext :: NameUse alpha = extTree
      loc.mbVal   = lookup ext.nm lhs.finEnv
      ext.value   = maybe undefined id loc.mbVal
      ext.errors  = if isNothing loc.mbVal then ["missing: " ++ ext.nm]
  
  sem_Expr_Var nm =
    sem :: Expr
      lhs.nmTree =  sem_Name_Use $
                    sem :: NameUse Type  -- nested sem
                      lhs.nm     = nm
                      loc.errors = lhs.errors
                      loc.value  = lhs.value
      ... = loc.errors  -- local attributes
      ... = loc.value   -- shared with nested sem
  \end{code}}
\end{frame}

\begin{frame}
  \frametitle{Referentially transparent?}

  \begin{itemize}
  \item Unable to guarantee that nested sem is executed exactly once
  \item We can guarantee referential transparency
        \begin{itemize}
        \item Requirement: code is ``orderable''
        \item Then: ``an expression for an attribute can be replaced with its value,
              without affecting the program''
        \end{itemize}
  \item Referential transparency is important!
  \end{itemize}
\end{frame}