diff options
Diffstat (limited to 'paper/patterns.tex')
| -rw-r--r-- | paper/patterns.tex | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/paper/patterns.tex b/paper/patterns.tex index e1aa767..2937fd0 100644 --- a/paper/patterns.tex +++ b/paper/patterns.tex @@ -10,7 +10,7 @@ sister(X,Y):- % X is Y’s sister when: X \textbackslash{}= Y. % X and Y are not the same person. \end{Verbatim} -Figure~\ref{fig:sister} shows the program’s AST with two patterns. The pattern drawn with blue dotted arrows encodes the fact that the first argument to the \code{sister} predicate also appears in the call to \code{female}. In other words, this pattern states that \code{X} must be female to be a sister. We write this pattern as the s-expression +Figure~\ref{fig:sister} shows the program’s AST with two patterns. The pattern drawn with blue dotted arrows encodes the fact that the first argument to the \code{sister} predicate also appears as the first argument in the call to \code{female}. In other words, this pattern states that \code{X} must be female to be a sister. We write this pattern as the s-expression \begin{Verbatim}[fontfamily=sf] (clause (head (compound (functor ‘\code{sister}’) (args var))) @@ -68,9 +68,9 @@ Figure~\ref{fig:sister} shows the program’s AST with two patterns. The pattern \label{fig:sister} \end{figure} -Every pattern used in this paper has the same basic structure, and describes paths from a \textsf{clause} node to one or two leaf nodes containing variables or values. All patterns in Figs.~\ref{fig:sister} and~\ref{fig:sum} are induced from such node pairs. For each leaf we also include some local context, for example the predicate name (e.g. \texttt{parent}). +Every pattern used in this paper has the same basic structure, and describes paths from a \textsf{clause} node to one or two leaf nodes containing variables or values. All patterns in Figs.~\ref{fig:sister} and~\ref{fig:sum} are induced from such pairs of nodes. For each leaf we also include some local context, such as the name of the predicate (e.g. \texttt{parent}) and the operators used in \textsf{unop} and \textsf{binop} nodes. -We regard these patterns as the smallest units of meaning in Prolog programs: each pattern encodes some interaction between two parts of the program. Including more than two leaf nodes in a pattern could make it difficult to pinpoint the exact error when generating hints. Each pattern contains at most two \textsf{var} nodes, so we require they both refer to the same variable -- relating two nodes with different variables would not tell us much about the program. This allows us to omit variable names from patterns. +We regard these patterns as the smallest units of meaning in Prolog programs: each pattern encodes some interaction between two objects (variable or value) in the program. Including more than two leaf nodes in a pattern could make it difficult to pinpoint the exact error when generating hints. Each pattern contains at most two \textsf{var} nodes, so we require they both refer to the same variable -- relating two nodes with different variables would not tell us much about the program. We can thus omit actual variable names from patterns. We handle syntactic variations in programs by omitting certain nodes from patterns. For example, by not including \textsf{and} nodes, the above pattern can match a clause regardless of the presence (or order) of other goals in its body (i.e., with any arrangement of \textsf{and} nodes in the AST). Order \emph{is} important for the nodes specified in the pattern; this is explained below. |