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correzioni Gabriel #2

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Francesco Mecca 2020-04-12 23:20:37 +02:00
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@ -1,4 +1,4 @@
% Created 2020-04-11 Sat 00:31
% Created 2020-04-12 Sun 22:50
% Intended LaTeX compiler: pdflatex
\documentclass[11pt]{article}
\usepackage[utf8]{inputenc}
@ -64,11 +64,11 @@ xleftmargin=1em,
\begin{document}
\section{Translation validation of the Pattern Matching Compiler}
\label{sec:org9d32dd4}
\label{sec:org02550ae}
\subsection{Source program}
\label{sec:org0032637}
The algorithm takes as its input a source program and translates it
\label{sec:org8c14d2a}
Our algorithm takes as its input a source program and translates it
into an algebraic data structure which type we call \emph{decision\_tree}.
\begin{verbatim}
@ -88,15 +88,15 @@ We distinguish
\item Leaf: a value matching this part results into the evaluation of a
source black box of code
\end{itemize}
The algorithm doesn't support type-declaration-based analysis
Our algorithm doesn't support type-declaration-based analysis
to know the list of constructors at a given type.
Let's consider some trivial examples:
\begin{verbatim}
function true -> 1
\end{verbatim}
\begin{center}
\begin{tabular}{l}
function true -> 1\\
\end{tabular}
\end{center}
is translated to
\begin{center}
\begin{tabular}{l}
@ -104,28 +104,36 @@ Switch ([(true, Leaf 1)], Failure)\\
\end{tabular}
\end{center}
while
\begin{verbatim}
function
true -> 1
| false -> 2
\end{verbatim}
\begin{center}
\begin{tabular}{l}
function\\
\(\vert{}\) true -> 1\\
\(\vert{}\) false -> 2\\
\end{tabular}
\end{center}
will be translated to
\begin{center}
\begin{tabular}{l}
Switch ([(true, Leaf 1); (false, Leaf 2)])\\
\end{tabular}
\end{center}
It is possible to produce Unreachable examples by using
refutation clauses (a "dot" in the right-hand-side)
\begin{verbatim}
function
true -> 1
| false -> 2
| _ -> .
\end{verbatim}
\begin{center}
\begin{tabular}{l}
function\\
\(\vert{}\) true -> 1\\
\(\vert{}\) false -> 2\\
\(\vert{}\) \_ -> .\\
\end{tabular}
\end{center}
that gets translated into
Switch ([(true, Leaf 1); (false, Leaf 2)], Unreachable)
\begin{center}
\begin{tabular}{l}
Switch ([(true, Leaf 1); (false, Leaf 2)], Unreachable)\\
\end{tabular}
\end{center}
We trust this annotation, which is reasonable as the type-checker
verifies that it indeed holds.
@ -139,7 +147,6 @@ true.
\begin{comment}
[ ] Finisci con Switch
[ ] Spiega del fallback
[ ] rivedi compilazione per tenere in considerazione il tuo albero invece che le Lambda
\end{comment}
The source code of a pattern matching function has the
@ -184,8 +191,7 @@ pattern1 ::= "\(\vert{}\)" clause\\
clause ::= lexpr "->" rexpr\\
lexpr ::= rule ($\varepsilon$\(\vert{}\)condition)\\
rexpr ::= \_code ;; arbitrary code\\
rule ::= wildcard\(\vert{}\)variable\(\vert{}\)constructor\_pattern\(\vert{}\)\{\}or\_pattern ;;\\
;; rules\\
rule ::= wildcard\(\vert{}\)variable\(\vert{}\)constructor\_pattern\(\vert{}\) or\_pattern ;;\\
wildcard ::= "\_"\\
variable ::= identifier\\
constructor\_pattern ::= constructor (rule\(\vert{}\)$\varepsilon$) (assignment\(\vert{}\)$\varepsilon$)\\
@ -196,59 +202,155 @@ assignment ::= "as" id\\
bexpr ::= \_code ;; arbitrary code\\
\end{tabular}
\end{center}
A source program t$_S$ is a collection of pattern clauses pointing to
\emph{bb} terms. Running a program t$_S$ against an input value v$_S$ produces as
a result \emph{r}:
The source program is parsed using the ocaml-compiler-libs library.
The result of parsing, when successful, results in a list of clauses
and a list of type declarations.
Every clause consists of three objects: a left-hand-side that is the
kind of pattern expressed, an option guard and a right-hand-side expression.
Patterns are encoded in the following way:
\begin{center}
\begin{tabular}{l}
t$_S$ ::= (p $\to$ bb)\(^{\text{i$\in $I}}\)\\
p ::= \(\vert{}\) K(p$_i$)$^i$, i $\in $ I \(\vert{}\) (p\(\vert{}\)q) \(\vert{}\) n $\in $ $\mathbb{N}$\\
r ::= guard list * (Match bb \(\vert{}\) NoMatch \(\vert{}\) Absurd)\\
t$_S$(v$_S$) $\to$ r\\
\begin{tabular}{ll}
pattern & type\\
\hline
\_ & Wildcard\\
p$_1$ as x & Assignment\\
c(p$_1$,p$_2$,\ldots{},p$_n$) & Constructor\\
(p$_1$\(\vert{}\) p$_2$) & Orpat\\
\end{tabular}
\end{center}
TODO: argument on what it means to run a source program
\emph{guard} and \emph{bb} expressions are treated as blackboxes of OCaml code.
A sound approach for treating these blackboxes would be to inspect the
OCaml compiler during translation to Lambda code and extract the
blackboxes compiled in their Lambda representation.
This would allow to test for equality with the respective blackbox at
the target level.
Given that this level of introspection is currently not possibile, we
decided to restrict the structure of blackboxes to the following (valid) OCaml
code:
Once parsed, the type declarations and the list of clauses are encoded in the form of a matrix
that is later evaluated using a matrix decomposition algorithm.
\begin{verbatim}
external guard : 'a -> 'b = "guard"
external observe : 'a -> 'b = "observe"
\end{verbatim}
Patterns are of the form
\begin{center}
\begin{tabular}{ll}
pattern & type of pattern\\
\hline
\_ & wildcard\\
x & variable\\
c(p$_1$,p$_2$,\ldots{},p$_n$) & constructor pattern\\
(p$_1$\(\vert{}\) p$_2$) & or-pattern\\
\end{tabular}
\end{center}
We assume these two external functions \emph{guard} and \emph{observe} with a valid
type that lets the user pass any number of arguments to them.
All the guards are of the form \texttt{guard <arg> <arg> <arg>}, where the
<arg> are expressed using the OCaml pattern matching language.
Similarly, all the right-hand-side expressions are of the form
\texttt{observe <arg> <arg> ...} with the same constraints on arguments.
The pattern \emph{p} matches a value \emph{v}, written as p $\preccurlyeq$ v, when one of the
following rules apply
\begin{verbatim}
type t = K1 | K2 of t (* declaration of an algebraic and recursive datatype t *)
\begin{center}
\begin{tabular}{llll}
\hline
\_ & $\preccurlyeq$ & v & $\forall$v\\
x & $\preccurlyeq$ & v & $\forall$v\\
(p$_1$ \(\vert{}\) p$_2$) & $\preccurlyeq$ & v & iff p$_1$ $\preccurlyeq$ v or p$_2$ $\preccurlyeq$ v\\
c(p$_1$, p$_2$, \ldots{}, p$_a$) & $\preccurlyeq$ & c(v$_1$, v$_2$, \ldots{}, v$_a$) & iff (p$_1$, p$_2$, \ldots{}, p$_a$) $\preccurlyeq$ (v$_1$, v$_2$, \ldots{}, v$_a$)\\
(p$_1$, p$_2$, \ldots{}, p$_a$) & $\preccurlyeq$ & (v$_1$, v$_2$, \ldots{}, v$_a$) & iff p$_i$ $\preccurlyeq$ v$_i$ $\forall$i $\in $ [1..a]\\
\hline
\end{tabular}
\end{center}
let _ = function
| K1 -> observe 0
| K2 K1 -> observe 1
| K2 x when guard x -> observe 2
| K2 (K2 x) as y when guard x y -> observe 3
| K2 _ -> observe 4
\end{verbatim}
When a value \emph{v} matches pattern \emph{p} we say that \emph{v} is an \emph{instance} of \emph{p}.
During compilation by the translators, expressions at the
right-hand-side are compiled into
Lambda code and are referred as lambda code actions l$_i$.
We define the \emph{pattern matrix} P as the matrix |m x n| where m bigger
or equal than the number of clauses in the source program and n is
equal to the arity of the constructor with the gratest arity.
\begin{equation*}
P =
\begin{pmatrix}
p_{1,1} & p_{1,2} & \cdots & p_{1,n} \\
p_{2,1} & p_{2,2} & \cdots & p_{2,n} \\
\vdots & \vdots & \ddots & \vdots \\
p_{m,1} & p_{m,2} & \cdots & p_{m,n} )
\end{pmatrix}
\end{equation*}
every row of \emph{P} is called a pattern vector
\(\vec{p_i}\) = (p$_1$, p$_2$, \ldots{}, p$_n$); In every instance of P pattern
vectors appear normalized on the length of the longest pattern vector.
Considering the pattern matrix P we say that the value vector
\(\vec{v}\) = (v$_1$, v$_2$, \ldots{}, v$_i$) matches the pattern vector p$_i$ in P if and only if the following two
conditions are satisfied:
\begin{itemize}
\item p\(_{\text{i,1}}\), p\(_{\text{i,2}}\), \(\cdots{}\), p\(_{\text{i,n}}\) $\preccurlyeq$ (v$_1$, v$_2$, \ldots{}, v$_i$)
\item $\forall$j < i p\(_{\text{j,1}}\), p\(_{\text{j,2}}\), \(\cdots{}\), p\(_{\text{j,n}}\) $\npreceq$ (v$_1$, v$_2$, \ldots{}, v$_i$)
\end{itemize}
We can define the following three relations with respect to patterns:
\begin{itemize}
\item Pattern p is less precise than pattern q, written p $\preccurlyeq$ q, when all
instances of q are instances of p
\item Pattern p and q are equivalent, written p $\equiv$ q, when their instances
are the same
\item Patterns p and q are compatible when they share a common instance
\end{itemize}
Wit the support of two auxiliary functions
\begin{itemize}
\item tail of an ordered family
\begin{center}
\begin{tabular}{l}
tail((x$_i$)\(^{\text{i $\in $ I}}\)) := (x$_i$)\(^{\text{i $\ne$ min(I)}}\)\\
\end{tabular}
\end{center}
\item first non-$\bot$ element of an ordered family
\begin{center}
\begin{tabular}{l}
First((x$_i$)$^i$) := $\bot$ \quad \quad \quad if $\forall$i, x$_i$ = $\bot$\\
First((x$_i$)$^i$) := x\_min\{i \(\vert{}\) x$_i$ $\ne$ $\bot$\} \quad if $\exists$i, x$_i$ $\ne$ $\bot$\\
\end{tabular}
\end{center}
\end{itemize}
we now define what it means to run a pattern row against a value
vector of the same length, that is (p$_i$)$^i$(v$_i$)$^i$
\begin{center}
\begin{tabular}{lll}
p$_i$ & v$_i$ & result\(_{\text{pat}}\)\\
\hline
$\varnothing$ & ($\varnothing$) & []\\
(\_, tail(p$_i$)$^i$) & (v$_i$) & tail(p$_i$)$^i$(tail(v$_i$)$^i$)\\
(x, tail(p$_i$)$^i$) & (v$_i$) & $\sigma$[x$\mapsto$v$_0$] if tail(p$_i$)$^i$(tail(v$_i$)$^i$) = $\sigma$\\
(K(q$_j$)$^j$, tail(p$_i$)$^i$) & (K(v'$_j$)$^j$,tail(v$_j$)$^j$) & ((q$_j$)$^j$ \sout{+} tail(p$_i$)$^i$)((v'$_j$)$^j$ \sout{+} tail(v$_i$)$^i$)\\
(K(q$_j$)$^j$, tail(p$_i$)$^i$) & (K'(v'$_l$)$^l$,tail(v$_j$)$^j$) & $\bot$ if K $\ne$ K'\\
(q$_1$\(\vert{}\)q$_2$, tail(p$_i$)$^i$) & (v$_i$)$^i$ & First((q$_1$,tail(p$_i$)$^i$)(v$_i$)$^i$, (q$_2$,tail(p$_i$)$^i$)(v$_i$)$^i$)\\
\end{tabular}
\end{center}
A source program t$_S$ is a collection of pattern clauses pointing to
\emph{bb} terms. Running a program t$_S$ against an input value v$_S$, written
t$_S$(v$_S$) produces a result \emph{r} belonging to the following grammar:
\begin{center}
\begin{tabular}{l}
t$_S$ ::= (p $\to$ bb)\(^{\text{i$\in $I}}\)\\
t$_S$(v$_S$) $\to$ r\\
r ::= guard list * (Match bb \(\vert{}\) NoMatch \(\vert{}\) Absurd)\\
\end{tabular}
\end{center}
\begin{comment}
TODO: understand how to explain guard
\end{comment}
We can define what it means to run an input value v$_S$ against a source
program t$_S$:
\begin{center}
\begin{tabular}{l}
t$_S$(v$_S$) := $\bot$ \quad \quad \quad if $\forall$i, p$_i$(v$_S$) = $\bot$\\
First((x$_i$)$^i$) := x\_min\{i \(\vert{}\) x$_i$ $\ne$ $\bot$\} \quad if $\exists$i, x$_i$ $\ne$ $\bot$\\
t$_S$(v$_S$) = Absurd if bb\_min\{p$_i$ $\to$ bb$_i$ \(\vert{}\) p$_i$(v$_S$) $\ne$ $\bot$\} = \emph{refutation clause}\\
t$_S$(v$_S$) = Match bb\_min\{p$_i$ $\to$ bb$_i$ \(\vert{}\) p$_i$(v$_S$) $\ne$ $\bot$\}\\
\end{tabular}
\end{center}
[ \ldots{} ] Big part that I think doesn't need revision from you [ \ldots{} ]
In our prototype we make use of accessors to encode stored values.
\begin{minipage}{0.2\linewidth}
\begin{minipage}{0.6\linewidth}
\begin{verbatim}
let value = 1 :: 2 :: 3 :: []
(* that can also be written *)
let value = []
@ -351,49 +453,86 @@ because a source matrix in the case of empty rows returns
the first expression and (Leaf bb)(v) := Match bb
\item\relax [| (a$_j$)$^j$, $\varnothing$ |] $\equiv$ Failure
\end{enumerate}
Regarding non base cases:
Let's first define
Let's first define some auxiliary functions
\begin{itemize}
\item The index family of a constructor
\begin{center}
\begin{tabular}{l}
let Idx(k) := [0; arity(k)[\\
let First($\varnothing$) := $\bot$\\
let First((a$_j$)$^j$) := a\(_{\text{min(j$\in $J$\ne$$\varnothing$)}}\)\\
Idx(K) := [0; arity(K)[\\
\end{tabular}
\end{center}
\[
m := ((a_i)^i ((p_{ij})^i \to e_j)^{ij})
\]
\[
(k_k)^k := headconstructor(p_{i0})^i
\]
\begin{equation}
Groups(m) := ( k_k \to ((a)_{0.l})^{l \in Idx(k_k)} +++ (a_i)^{i \in I\DZ}), \\
( if p_{0j} is k(q_l) then \\
(q_l)^{l \in Idx(k_k)} +++ (p_{ij})^{i \in I\DZ} \to e_j \\
if p_{0j} is \_ then \\
(\_)^{l \in Idx(k_k)} +++ (p_{ij})^{i \in I\DZ} \to e_j \\
else \bot )^j ), \\
((a_i)^{i \in I\DZ}, ((p_{ij})^{i \in I\DZ} \to e_j if p_{0j} is \_ else \bot)^{j \in J})
\end{equation}
Groups(m) is an auxiliary function that source a matrix m into
\item head of an ordered family (we write x for any object here, value, pattern etc.)
\begin{center}
\begin{tabular}{l}
head((x$_i$)\(^{\text{i $\in $ I}}\)) = x\_min(I)\\
\end{tabular}
\end{center}
\item tail of an ordered family
\begin{center}
\begin{tabular}{l}
tail((x$_i$)\(^{\text{i $\in $ I}}\)) := (x$_i$)\(^{\text{i $\ne$ min(I)}}\)\\
\end{tabular}
\end{center}
\item head constructor of a value or pattern
\begin{center}
\begin{tabular}{l}
constr(K(x$_i$)$^i$) = K\\
constr(\_) = $\bot$\\
constr(x) = $\bot$\\
\end{tabular}
\end{center}
\item first non-$\bot$ element of an ordered family
\begin{center}
\begin{tabular}{l}
First((x$_i$)$^i$) := $\bot$ \quad \quad \quad if $\forall$i, x$_i$ = $\bot$\\
First((x$_i$)$^i$) := x\_min\{i \(\vert{}\) x$_i$ $\ne$ $\bot$\} \quad if $\exists$i, x$_i$ $\ne$ $\bot$\\
\end{tabular}
\end{center}
\item definition of group decomposition:
\end{itemize}
\begin{center}
\begin{tabular}{l}
let constrs((p$_i$)\(^{\text{i $\in $ I}}\)) = \{ K \(\vert{}\) K = constr(p$_i$), i $\in $ I \}\\
let Groups(m) where m = ((a$_i$)$^i$ ((p$_i$$_j$)$^i$ $\to$ e$_j$)$^i$$^j$) =\\
\quad \quad let (K$_k$)$^k$ = constrs(p$_i$$_0$)$^i$ in\\
\quad \quad ( K$_k$ $\to$\\
\quad \quad \quad \quad ((a$_0$.$_l$)$^l$ \sout{+} tail(a$_i$)$^i$)\\
\quad \quad \quad \quad (\\
\quad \quad \quad \quad if p$_o$$_j$ is K$_k$(q$_l$) then\\
\quad \quad \quad \quad \quad \quad (q$_l$)$^l$ \sout{+} tail(p$_i$$_j$)$^i$ $\to$ e$_j$\\
\quad \quad \quad \quad if p$_o$$_j$ is \_ then\\
\quad \quad \quad \quad \quad \quad (\_)$^l$ \sout{+} tail(p$_i$$_j$)$^i$ $\to$ e$_j$\\
\quad \quad \quad \quad else $\bot$\\
\quad \quad \quad \quad )$^j$\\
\quad \quad ), (\\
\quad \quad \quad \quad tail(a$_i$)$^i$, (tail(p$_i$$_j$)$^i$ $\to$ e$_j$ if p$_0$$_j$ is \_ else $\bot$)$^j$\\
\quad \quad )\\
\end{tabular}
\end{center}
Groups(m) is an auxiliary function that decomposes a matrix m into
submatrices, according to the head constructor of their first pattern.
Groups(m) returns one submatrix m\_r for each head constructor k that
Groups(m) returns one submatrix m\_r for each head constructor K that
occurs on the first row of m, plus one "wildcard submatrix" m\(_{\text{wild}}\)
that matches on all values that do not start with one of those head
constructors.
Intuitively, m is equivalent to its decomposition in the following
sense: if the first pattern of an input vector (v$_i$)$^i$ starts with one
of the head constructors k, then running (v$_i$)$^i$ against m is the same
as running it against the submatrix m$_k$; otherwise (its head
constructor is none of the k) it is equivalent to running it against
sense: if the first pattern of an input vector (v\_i)\^{}i starts with one
of the head constructors K$_k$, then running (v\_i)\^{}i against m is the same
as running it against the submatrix m\(_{\text{K$_k$}}\); otherwise (its head
constructor $\notin$ (K$_k$)$^k$) it is equivalent to running it against
the wildcard submatrix.
We formalize this intuition as follows:
Lemma (Groups):
Let \[m\] be a matrix with \[Groups(m) = (k_r \to m_r)^k, m_{wild}\].
We formalize this intuition as follows
\begin{enumerate}
\item Lemma (Groups):
\label{sec:org3d5a08a}
Let \emph{m} be a matrix with
\begin{center}
\begin{tabular}{l}
Groups(m) = (k\_r \(\to\) m\_r)\^{}k, m\(_{\text{wild}}\)\\
\end{tabular}
\end{center}
For any value vector \((v_i)^l\) such that \(v_0 = k(v'_l)^l\) for some
constructor k,
we have:
@ -410,69 +549,99 @@ if k = k$_k$ \text{ for some k then}\\
TODO: fix \{0}
\end{comment}
\begin{enumerate}
\item Proof:
\label{sec:orgb73fb4f}
Let \(m\) be a matrix with \[Group(m) = (k_r \to m_r)^k, m_{wild}\]
Let \((v_i)^i\) be an input matrix with \(v_0 = k(v'_l)^l\) for some k.
We proceed by case analysis:
\label{sec:org416e0ec}
Let \emph{m} be a matrix ((a$_i$)$^i$, ((p$_i$$_j$)$^i$ $\to$ e$_j$)$^j$) with
\begin{center}
\begin{tabular}{l}
Groups(m) = (K$_k$ $\to$ m$_k$)$^k$, m\(_{\text{wild}}\)\\
\end{tabular}
\end{center}
Below we are going to assume that m is a simplified matrix such that
the first row does not contain an or-pattern or a binding to a
variable.
Let (v$_i$)$^i$ be an input matrix with v$_0$ = K$_v$(v'\(_{\text{l}}\))$^l$ for some constructor K$_v$.
We have to show that:
\begin{itemize}
\item either k is one of the k$_k$ for some k
\item or k is none of the (k$_k$)$^k$
\item if K$_k$ = K$_v$ for some K$_k$ $\in $ constrs(p$_0$$_j$)$^j$, then
m(v$_i$)$^i$ = m$_k$((v'$_l$)$^l$ \sout{+} tail(v$_i$)$^i$)
\item otherwise
m(v$_i$)$^i$ = m\(_{\text{wild}}\)(tail(v$_i$)$^i$)
\end{itemize}
Let us call (r$_k$$_j$) the j-th row of the submatrix m$_k$, and r$_j$\(_{\text{wild}}\)
the j-th row of the wildcard submatrix m\(_{\text{wild}}\).
Both m(v$_i$)$^i$ and m$_k$(v$_k$)$^k$ are defined as the first matching result of
a family over each row r$_j$ of a matrix
We know, from the definition of
Groups(m), that m$_k$ is
Our goal contains same-behavior equalities between matrices, for
a fixed input vector (v$_i$)$^i$. It suffices to show same-behavior
equalities between each row of the matrices for this input
vector. We show that for any j,
\begin{itemize}
\item if K$_k$ = K$_v$ for some K$_k$ $\in $ constrs(p$_0$$_j$)$^j$, then
\begin{center}
\begin{tabular}{l}
((a)\{0.l\})\(^{\text{l$\in $Idx(k$_k$)}}\) \sout{+} (a$_i$)\(^{\text{i$\in $I}\DZ}\)),\\
(\\
\quad if p\(_{\text{0j}}\) is k(q$_l$) then\\
\quad \quad (q$_l$)$^l$ \sout{+} (p\(_{\text{ij}}\))\(^{\text{i$\in $I}\DZ\ }\) $\to$ e$_j$\\
\quad if p\(_{\text{0j}}\) is \_ then\\
\quad \quad (\_)$^l$ \sout{+} (p\(_{\text{ij}}\))\(^{\text{i$\in $I}\DZ}\) $\to$ e$_j$\\
\quad else $\bot$\\
)\(^{\text{j$\in $J}}\)\\
(p$_i$$_j$)$^i$(v$_i$)$^i$ = r$_k$$_j$((v'$_l$)$^l$ \sout{+} tail(v$_i$)$^i$\\
\end{tabular}
\end{center}
\item otherwise
\begin{center}
\begin{tabular}{l}
(p$_i$$_j$)$^i$(v$_i$)$^i$ = r$_j$\(_{\text{wild}}\) tail(v$_i$)$^i$\\
\end{tabular}
\end{center}
\end{itemize}
In the first case (K$_v$ is K$_k$ for some K$_k$ $\in $ constrs(p$_0$$_j$)$^j$), we
have to prove that
\begin{center}
\begin{tabular}{l}
(p$_i$$_j$)$^i$(v$_i$)$^i$ = r$_k$$_j$((v'$_l$)$^l$ \sout{+} tail(v$_i$)$^i$\\
\end{tabular}
\end{center}
By definition of m$_k$ we know that r$_k$$_j$ is equal to
\begin{center}
\begin{tabular}{l}
if p$_o$$_j$ is K$_k$(q$_l$) then\\
\quad (q$_l$)$^l$ \sout{+} tail(p$_i$$_j$)$^i$ $\to$ e$_j$\\
if p$_o$$_j$ is \_ then\\
\quad (\_)$^l$ \sout{+} tail(p$_i$$_j$)$^i$ $\to$ e$_j$\\
else $\bot$\\
\end{tabular}
\end{center}
\begin{comment}
Maybe better as a table?
| p$_o$$_j$ | r$_k$$_j$ |
|--------+---------------------------|
| K$_k$(q$_l$) | (q$_l$)$^l$ +++ tail(p$_i$$_j$)$^i$ $\to$ e$_j$ |
| _ | (_)$^l$ +++ tail(p$_i$$_j$)$^i$ $\to$ e$_j$ |
| else | $\bot$ |
\end{comment}
By definition of (p$_i$)$^i$(v$_i$)$^i$ we know that (p$_i$$_j$)$^i$(v$_i$) is equal to
\begin{center}
\begin{tabular}{l}
(K(q$_j$)$^j$, tail(p$_i$$_j$)$^i$) (K(v'$_l$)$^l$,tail(v$_i$)$^i$) := ((q$_j$)$^j$ \sout{+} tail(p$_i$$_j$)$^i$)((v'$_l$)$^l$ \sout{+} tail(v$_i$)$^i$)\\
(\_, tail(p$_i$$_j$)$^i$) (v$_i$) := tail(p$_i$$_j$)$^i$(tail(v$_i$)$^i$)\\
(K(q$_j$)$^j$, tail(p$_i$$_j$)$^i$) (K'(v'$_l$)$^l$,tail(v$_j$)$^j$) := $\bot$ if K $\ne$ K'\\
\end{tabular}
\end{center}
By definition, m(v$_i$)$^i$ is
We prove this first case by a second case analysis on p$_0$$_j$.
TODO
In the second case (K$_v$ is distinct from K$_k$ for all K$_k$ $\in $ constrs(p$_o$$_j$)$^j$),
we have to prove that
\begin{center}
\begin{tabular}{l}
m(v$_i$)$^i$ = First(r$_j$(v$_i$)$^i$)$^j$ for m = ((a$_i$)$^i$, (r$_j$)$^j$)\\
(p$_i$)$^i$ (v$_i$)$^i$ = \{\\
\quad if p$_0$ = k(q$_l$)$^l$, v$_0$ = k'(v'$_k$)$^k$, k=Idx(k') and l=Idx(k)\\
\quad \quad if k $\ne$ k' then $\bot$\\
if k = k' then ((q$_l$)$^l$ \sout{+} (p$_i$)\(^{\text{i$\in $I}\DZ}\)) ((v'$_k$)$^k$ \sout{+} (v$_i$)\(^{\text{i$\in $I}\DZ}\) )\\
if p$_0$ = (q$_1$\(\vert{}\)q$_2$) then\\
First( (q$_1$p$_i$\(^{\text{i$\in $I}\DZ}\)) v$_i$\(^{\text{i$\in $I}\DZ}\), (q$_2$p$_i$\(^{\text{i$\in $I }\DZ}\)) v$_i$\(^{\text{i$\in $I}\DZ}\))\}\\
(p$_i$$_j$)$^i$(v$_i$)$^i$ = r$_j$\(_{\text{wild}}\) tail(v$_i$)$^i$\\
\end{tabular}
\end{center}
For this reason, if we can prove that
\begin{center}
\begin{tabular}{l}
$\forall$j, r$_j$(v$_i$)$^i$ = r'$_j$((v'$_k$)$^k$ ++ (v$_i$)$^i$)\\
\end{tabular}
\end{center}
it follows that
\begin{center}
\begin{tabular}{l}
m(v$_i$)$^i$ = m$_k$((v'$_k$)$^k$ ++ (v$_i$)$^i$)\\
\end{tabular}
\end{center}
from the above definition.
We can also show that a$_i$ = (a\(_{\text{0.l}}\))$^l$ \sout{+} a\(_{\text{i$\in $I}\DZ}\) because v(a$_0$) = K(v(a)\{0.l\})$^l$)
TODO
\end{enumerate}
\subsection{Target translation}
\label{sec:org0337fa8}
\label{sec:org7394f38}
The target program of the following general form is parsed using a parser
generated by Menhir, a LR(1) parser generator for the OCaml programming language.
@ -560,12 +729,12 @@ $\forall$v$_T$, t$_T$(v$_T$) = $\llbracket$t$_T$$\rrbracket$$_T$(v$_T$)\\
\subsection{Equivalence checking}
\label{sec:org7268798}
\label{sec:org7194f33}
The equivalence checking algorithm takes as input a domain of
possible values \emph{S} and a pair of source and target decision trees and
in case the two trees are not equivalent it returns a counter example.
The algorithm respects the following correctness statement:
Our algorithm respects the following correctness statement:
\begin{comment}
TODO: we have to define what \coversTEX mean for readers to understand the specifications
@ -699,22 +868,21 @@ We say that C$_T$ covers the input space \emph{S}, written
\emph{covers(C$_T$, S)} when every value v$_S$$\in $S is a valid input to the
decision tree C$_T$. (TODO: rephrase)
Given an input space \emph{S} and a couple of decision trees, where
the target decision tree C$_T$ covers the input space \emph{S}, we say that
the two decision trees are equivalent when:
the target decision tree C$_T$ covers the input space \emph{S} we can define equivalence:
\begin{center}
\begin{tabular}{l}
equiv(S, C$_S$, C$_T$, gs) = Yes $\wedge$ covers(C$_T$, S) $\to$ $\forall$v$_S$$\simeq$v$_T$ $\in $ S, C$_S$(v$_S$) $\simeq$gs C$_T$(v$_T$)\\
\end{tabular}
\end{center}
Similarly we say that a couple of decision trees in the presence of
an input space \emph{S} are \emph{not} equivalent when:
an input space \emph{S} are \emph{not} equivalent in the following way:
\begin{center}
\begin{tabular}{l}
equiv(S, C$_S$, C$_T$, gs) = No(v$_S$,v$_T$) $\wedge$ covers(C$_T$, S) $\to$ v$_S$$\simeq$v$_T$ $\in $ S $\wedge$ C$_S$(v$_S$) $\ne$gs C$_T$(v$_T$)\\
\end{tabular}
\end{center}
Corollary: For a full input space \emph{S}, that is the universe of the
target program we say:
target program:
\begin{center}
\begin{tabular}{l}
equiv(S, $\llbracket$t$_S$$\rrbracket$$_S$, $\llbracket$t$_T$$\rrbracket$$_T$, $\varnothing$) = Yes $\Leftrightarrow$ t$_S$ $\simeq$ t$_T$\\
@ -891,7 +1059,7 @@ equiv(S, Failure as C$_S$, Switch(a, ($\pi$$_i$ $\to$ C$_T$$_i$)\(^{\text{i$\in
equiv(S, Leaf bb$_S$ as C$_S$, Switch(a, ($\pi$$_i$ $\to$ C$_T$$_i$)\(^{\text{i$\in $I}}\))) := Forall(equiv( S$\cap$a$\to$$\pi$(k$_i$)), C$_S$, C$_T$$_i$)\(^{\text{i$\in $I}}\))\\
\end{tabular}
\end{center}
The algorithm either returns Yes for every sub-input space S$_i$ := S$\cap$(a$\to$$\pi$(k$_i$)) and
Our algorithm either returns Yes for every sub-input space S$_i$ := S$\cap$(a$\to$$\pi$(k$_i$)) and
subtree C$_T$$_i$
\begin{center}
\begin{tabular}{l}
@ -924,7 +1092,7 @@ values not covered but the union of the constructors k$_i$
$\pi$\(_{\text{fallback}}\) = ¬\bigcup\limits\(_{\text{i$\in $I}}\)$\pi$(k$_i$)\\
\end{tabular}
\end{center}
The algorithm proceeds by trimming
Our algorithm proceeds by trimming
\begin{center}
\begin{tabular}{l}
equiv(S, Switch(a, (k$_i$ $\to$ C$_S$$_i$)\(^{\text{i$\in $I}}\), C\(_{\text{sf}}\)), C$_T$) :=\\

343
tesi/gabriel/part4_unicode.org
View file

@ -46,7 +46,7 @@
* Translation validation of the Pattern Matching Compiler
** Source program
The algorithm takes as its input a source program and translates it
Our algorithm takes as its input a source program and translates it
into an algebraic data structure which type we call /decision_tree/.
#+BEGIN_SRC
@ -64,36 +64,28 @@ We distinguish
- Failure: a value matching this part results in an error
- Leaf: a value matching this part results into the evaluation of a
source black box of code
The algorithm doesn't support type-declaration-based analysis
Our algorithm doesn't support type-declaration-based analysis
to know the list of constructors at a given type.
Let's consider some trivial examples:
#+BEGIN_SRC
function true -> 1
#+END_SRC
| function true -> 1
is translated to
|Switch ([(true, Leaf 1)], Failure)
while
#+BEGIN_SRC
function
true -> 1
| false -> 2
#+END_SRC
| function
| \vert{} true -> 1
| \vert{} false -> 2
will be translated to
|Switch ([(true, Leaf 1); (false, Leaf 2)])
|Switch ([(true, Leaf 1); (false, Leaf 2)])
It is possible to produce Unreachable examples by using
refutation clauses (a "dot" in the right-hand-side)
#+BEGIN_SRC
function
true -> 1
| false -> 2
| _ -> .
#+END_SRC
|function
|\vert{} true -> 1
|\vert{} false -> 2
|\vert{} _ -> .
that gets translated into
Switch ([(true, Leaf 1); (false, Leaf 2)], Unreachable)
| Switch ([(true, Leaf 1); (false, Leaf 2)], Unreachable)
We trust this annotation, which is reasonable as the type-checker
verifies that it indeed holds.
@ -107,7 +99,6 @@ true.
\begin{comment}
[ ] Finisci con Switch
[ ] Spiega del fallback
[ ] rivedi compilazione per tenere in considerazione il tuo albero invece che le Lambda
\end{comment}
The source code of a pattern matching function has the
@ -142,8 +133,7 @@ This BNF grammar describes formally the grammar of the source program:
| clause ::= lexpr "->" rexpr
| lexpr ::= rule (ε\vert{}condition)
| rexpr ::= _code ;; arbitrary code
| rule ::= wildcard\vert{}variable\vert{}constructor_pattern\vert{}or_pattern ;;
| ;; rules
| rule ::= wildcard\vert{}variable\vert{}constructor_pattern\vert or_pattern ;;
| wildcard ::= "_"
| variable ::= identifier
| constructor_pattern ::= constructor (rule\vert{}ε) (assignment\vert{}ε)
@ -152,55 +142,117 @@ This BNF grammar describes formally the grammar of the source program:
| condition ::= "when" bexpr
| assignment ::= "as" id
| bexpr ::= _code ;; arbitrary code
The source program is parsed using the ocaml-compiler-libs library.
The result of parsing, when successful, results in a list of clauses
and a list of type declarations.
Every clause consists of three objects: a left-hand-side that is the
kind of pattern expressed, an option guard and a right-hand-side expression.
Patterns are encoded in the following way:
| pattern | type |
|-----------------+-------------|
| _ | Wildcard |
| p₁ as x | Assignment |
| c(p₁,p₂,...,pₙ) | Constructor |
| (p₁\vert p₂) | Orpat |
Once parsed, the type declarations and the list of clauses are encoded in the form of a matrix
that is later evaluated using a matrix decomposition algorithm.
Patterns are of the form
| pattern | type of pattern |
|-----------------+---------------------|
| _ | wildcard |
| x | variable |
| c(p₁,p₂,...,pₙ) | constructor pattern |
| (p₁\vert p₂) | or-pattern |
The pattern /p/ matches a value /v/, written as p ≼ v, when one of the
following rules apply
|--------------------+---+--------------------+-------------------------------------------|
| _ | ≼ | v | ∀v |
| x | ≼ | v | ∀v |
| (p₁ \vert p₂) | ≼ | v | iff p₁ ≼ v or p₂ ≼ v |
| c(p₁, p₂, ..., pₐ) | ≼ | c(v₁, v₂, ..., vₐ) | iff (p₁, p₂, ..., pₐ) ≼ (v₁, v₂, ..., vₐ) |
| (p₁, p₂, ..., pₐ) | ≼ | (v₁, v₂, ..., vₐ) | iff pᵢ ≼ vᵢ ∀i ∈ [1..a] |
|--------------------+---+--------------------+-------------------------------------------|
When a value /v/ matches pattern /p/ we say that /v/ is an /instance/ of /p/.
During compilation by the translators, expressions at the
right-hand-side are compiled into
Lambda code and are referred as lambda code actions lᵢ.
We define the /pattern matrix/ P as the matrix |m x n| where m bigger
or equal than the number of clauses in the source program and n is
equal to the arity of the constructor with the gratest arity.
\begin{equation*}
P =
\begin{pmatrix}
p_{1,1} & p_{1,2} & \cdots & p_{1,n} \\
p_{2,1} & p_{2,2} & \cdots & p_{2,n} \\
\vdots & \vdots & \ddots & \vdots \\
p_{m,1} & p_{m,2} & \cdots & p_{m,n} )
\end{pmatrix}
\end{equation*}
every row of /P/ is called a pattern vector
$\vec{p_i}$ = (p₁, p₂, ..., pₙ); In every instance of P pattern
vectors appear normalized on the length of the longest pattern vector.
Considering the pattern matrix P we say that the value vector
$\vec{v}$ = (v₁, v₂, ..., vᵢ) matches the pattern vector pᵢ in P if and only if the following two
conditions are satisfied:
- p_{i,1}, p_{i,2}, \cdots, p_{i,n} ≼ (v₁, v₂, ..., vᵢ)
- ∀j < i p_{j,1}, p_{j,2}, \cdots, p_{j,n} ⋠ (v₁, v₂, ..., vᵢ)
We can define the following three relations with respect to patterns:
- Pattern p is less precise than pattern q, written p ≼ q, when all
instances of q are instances of p
- Pattern p and q are equivalent, written p ≡ q, when their instances
are the same
- Patterns p and q are compatible when they share a common instance
Wit the support of two auxiliary functions
- tail of an ordered family
| tail((xᵢ)^{i ∈ I}) := (xᵢ)^{i ≠ min(I)}
- first non-⊥ element of an ordered family
| First((xᵢ)ⁱ) := ⊥ \quad \quad \quad if ∀i, xᵢ = ⊥
| First((xᵢ)ⁱ) := x_min{i \vert{} xᵢ ≠ ⊥} \quad if ∃i, xᵢ ≠ ⊥
we now define what it means to run a pattern row against a value
vector of the same length, that is (pᵢ)ⁱ(vᵢ)ⁱ
| pᵢ | vᵢ | result_{pat} |
|--------------------------+----------------------+-------------------------------------------------|
| ∅ | (∅) | [] |
| (_, tail(pᵢ)ⁱ) | (vᵢ) | tail(pᵢ)ⁱ(tail(vᵢ)ⁱ) |
| (x, tail(pᵢ)ⁱ) | (vᵢ) | σ[x↦v₀] if tail(pᵢ)ⁱ(tail(vᵢ)ⁱ) = σ |
| (K(qⱼ)ʲ, tail(pᵢ)ⁱ) | (K(v'ⱼ)ʲ,tail(vⱼ)ʲ) | ((qⱼ)ʲ +++ tail(pᵢ)ⁱ)((v'ⱼ)ʲ +++ tail(vᵢ)ⁱ) |
| (K(qⱼ)ʲ, tail(pᵢ)ⁱ) | (K'(v'ₗ)ˡ,tail(vⱼ)ʲ) | ⊥ if K ≠ K' |
| (q₁\vert{}q₂, tail(pᵢ)ⁱ) | (vᵢ)ⁱ | First((q₁,tail(pᵢ)ⁱ)(vᵢ)ⁱ, (q₂,tail(pᵢ)ⁱ)(vᵢ)ⁱ) |
A source program tₛ is a collection of pattern clauses pointing to
/bb/ terms. Running a program tₛ against an input value vₛ produces as
a result /r/:
/bb/ terms. Running a program tₛ against an input value vₛ, written
tₛ(vₛ) produces a result /r/ belonging to the following grammar:
| tₛ ::= (p → bb)^{i∈I}
| p ::= \vert K(pᵢ)ⁱ, i ∈ I \vert (p\vert{}q) \vert n ∈ ℕ
| r ::= guard list * (Match bb \vert{} NoMatch \vert{} Absurd)
| tₛ(vₛ) → r
| r ::= guard list * (Match bb \vert{} NoMatch \vert{} Absurd)
\begin{comment}
TODO: understand how to explain guard
\end{comment}
We can define what it means to run an input value vₛ against a source
program tₛ:
| tₛ(vₛ) := ⊥ \quad \quad \quad if ∀i, pᵢ(vₛ) = ⊥
| First((xᵢ)ⁱ) := x_min{i \vert{} xᵢ ≠ ⊥} \quad if ∃i, xᵢ ≠ ⊥
| tₛ(vₛ) = Absurd if bb_min{pᵢ → bbᵢ \vert{} pᵢ(vₛ) ≠ ⊥} = /refutation clause/
| tₛ(vₛ) = Match bb_min{pᵢ → bbᵢ \vert{} pᵢ(vₛ) ≠ ⊥}
TODO: argument on what it means to run a source program
/guard/ and /bb/ expressions are treated as blackboxes of OCaml code.
A sound approach for treating these blackboxes would be to inspect the
OCaml compiler during translation to Lambda code and extract the
blackboxes compiled in their Lambda representation.
This would allow to test for equality with the respective blackbox at
the target level.
Given that this level of introspection is currently not possibile, we
decided to restrict the structure of blackboxes to the following (valid) OCaml
code:
#+BEGIN_SRC
external guard : 'a -> 'b = "guard"
external observe : 'a -> 'b = "observe"
#+END_SRC
We assume these two external functions /guard/ and /observe/ with a valid
type that lets the user pass any number of arguments to them.
All the guards are of the form \texttt{guard <arg> <arg> <arg>}, where the
<arg> are expressed using the OCaml pattern matching language.
Similarly, all the right-hand-side expressions are of the form
\texttt{observe <arg> <arg> ...} with the same constraints on arguments.
#+BEGIN_SRC
type t = K1 | K2 of t (* declaration of an algebraic and recursive datatype t *)
let _ = function
| K1 -> observe 0
| K2 K1 -> observe 1
| K2 x when guard x -> observe 2
| K2 (K2 x) as y when guard x y -> observe 3
| K2 _ -> observe 4
#+END_SRC
[ ... ] Big part that I think doesn't need revision from you [ ... ]
In our prototype we make use of accessors to encode stored values.
\begin{minipage}{0.2\linewidth}
\begin{minipage}{0.6\linewidth}
\begin{verbatim}
let value = 1 :: 2 :: 3 :: []
(* that can also be written *)
let value = []
@ -277,45 +329,54 @@ Base cases:
because a source matrix in the case of empty rows returns
the first expression and (Leaf bb)(v) := Match bb
2. [| (aⱼ)ʲ, ∅ |] ≡ Failure
Regarding non base cases:
Let's first define
| let Idx(k) := [0; arity(k)[
| let First(∅) := ⊥
| let First((aⱼ)ʲ) := a_{min(j∈J≠∅)}
\[
m := ((a_i)^i ((p_{ij})^i \to e_j)^{ij})
\]
\[
(k_k)^k := headconstructor(p_{i0})^i
\]
\begin{equation}
Groups(m) := ( k_k \to ((a)_{0.l})^{l \in Idx(k_k)} +++ (a_i)^{i \in I\DZ}), \\
( if p_{0j} is k(q_l) then \\
(qₗ)^{l \in Idx(k_k)} +++ (p_{ij})^{i \in I\DZ} \to e_j \\
if p_{0j} is \_ then \\
(\_)^{l \in Idx(k_k)} +++ (p_{ij})^{i \in I\DZ} \to e_j \\
else \bot )^j ), \\
((a_i)^{i \in I\DZ}, ((p_{ij})^{i \in I\DZ} \to eⱼ if p_{0j} is \_ else \bot)^{j \in J})
\end{equation}
Groups(m) is an auxiliary function that source a matrix m into
Let's first define some auxiliary functions
- The index family of a constructor
| Idx(K) := [0; arity(K)[
- head of an ordered family (we write x for any object here, value, pattern etc.)
| head((xᵢ)^{i ∈ I}) = x_min(I)
- tail of an ordered family
| tail((xᵢ)^{i ∈ I}) := (xᵢ)^{i ≠ min(I)}
- head constructor of a value or pattern
| constr(K(xᵢ)ⁱ) = K
| constr(_) = ⊥
| constr(x) = ⊥
- first non-⊥ element of an ordered family
| First((xᵢ)ⁱ) := ⊥ \quad \quad \quad if ∀i, xᵢ = ⊥
| First((xᵢ)ⁱ) := x_min{i \vert{} xᵢ ≠ ⊥} \quad if ∃i, xᵢ ≠ ⊥
- definition of group decomposition:
| let constrs((pᵢ)^{i ∈ I}) = { K \vert{} K = constr(pᵢ), i ∈ I }
| let Groups(m) where m = ((aᵢ)ⁱ ((pᵢⱼ)ⁱ → eⱼ)ⁱʲ) =
| \quad \quad let (Kₖ)ᵏ = constrs(pᵢ₀)ⁱ in
| \quad \quad ( Kₖ →
| \quad \quad \quad \quad ((a₀.ₗ)ˡ +++ tail(aᵢ)ⁱ)
| \quad \quad \quad \quad (
| \quad \quad \quad \quad if pₒⱼ is Kₖ(qₗ) then
| \quad \quad \quad \quad \quad \quad (qₗ)ˡ +++ tail(pᵢⱼ)ⁱ → eⱼ
| \quad \quad \quad \quad if pₒⱼ is _ then
| \quad \quad \quad \quad \quad \quad (_)ˡ +++ tail(pᵢⱼ)ⁱ → eⱼ
| \quad \quad \quad \quad else ⊥
| \quad \quad \quad \quad )ʲ
| \quad \quad ), (
| \quad \quad \quad \quad tail(aᵢ)ⁱ, (tail(pᵢⱼ)ⁱ → eⱼ if p₀ⱼ is _ else ⊥)ʲ
| \quad \quad )
Groups(m) is an auxiliary function that decomposes a matrix m into
submatrices, according to the head constructor of their first pattern.
Groups(m) returns one submatrix m_r for each head constructor k that
Groups(m) returns one submatrix m_r for each head constructor K that
occurs on the first row of m, plus one "wildcard submatrix" m_{wild}
that matches on all values that do not start with one of those head
constructors.
Intuitively, m is equivalent to its decomposition in the following
sense: if the first pattern of an input vector (vᵢ)ⁱ starts with one
of the head constructors k, then running (vᵢ)ⁱ against m is the same
as running it against the submatrix mₖ; otherwise (its head
constructor is none of the k) it is equivalent to running it against
sense: if the first pattern of an input vector (v_i)^i starts with one
of the head constructors Kₖ, then running (v_i)^i against m is the same
as running it against the submatrix m_{Kₖ}; otherwise (its head
constructor ∉ (Kₖ)ᵏ) it is equivalent to running it against
the wildcard submatrix.
We formalize this intuition as follows:
Lemma (Groups):
Let \[m\] be a matrix with \[Groups(m) = (k_r \to m_r)^k, m_{wild}\].
We formalize this intuition as follows
*** Lemma (Groups):
Let /m/ be a matrix with
| Groups(m) = (k_r \to m_r)^k, m_{wild}
For any value vector $(v_i)^l$ such that $v_0 = k(v'_l)^l$ for some
constructor k,
we have:
@ -329,43 +390,60 @@ TODO: fix \{0}
\end{comment}
*** Proof:
Let $m$ be a matrix with \[Group(m) = (k_r \to m_r)^k, m_{wild}\]
Let $(v_i)^i$ be an input matrix with $v_0 = k(v'_l)^l$ for some k.
We proceed by case analysis:
- either k is one of the kₖ for some k
- or k is none of the (kₖ)ᵏ
Let /m/ be a matrix ((aᵢ)ⁱ, ((pᵢⱼ)ⁱ → eⱼ)ʲ) with
| Groups(m) = (Kₖ → mₖ)ᵏ, m_{wild}
Below we are going to assume that m is a simplified matrix such that
the first row does not contain an or-pattern or a binding to a
variable.
Both m(vᵢ)ⁱ and mₖ(vₖ)ᵏ are defined as the first matching result of
a family over each row rⱼ of a matrix
Let (vᵢ)ⁱ be an input matrix with v₀ = Kᵥ(v'_{l})ˡ for some constructor Kᵥ.
We have to show that:
- if Kₖ = Kᵥ for some Kₖ ∈ constrs(p₀ⱼ)ʲ, then
m(vᵢ)ⁱ = mₖ((v'ₗ)ˡ +++ tail(vᵢ)ⁱ)
- otherwise
m(vᵢ)ⁱ = m_{wild}(tail(vᵢ)ⁱ)
Let us call (rₖⱼ) the j-th row of the submatrix mₖ, and rⱼ_{wild}
the j-th row of the wildcard submatrix m_{wild}.
We know, from the definition of
Groups(m), that mₖ is
| ((a){0.l})^{l∈Idx(kₖ)} +++ (aᵢ)^{i∈I\DZ}),
| (
| \quad if p_{0j} is k(qₗ) then
| \quad \quad (qₗ)ˡ +++ (p_{ij})^{i∈I\DZ } → eⱼ
| \quad if p_{0j} is _ then
| \quad \quad (_)ˡ +++ (p_{ij})^{i∈I\DZ} → eⱼ
| \quad else ⊥
| )^{j∈J}
Our goal contains same-behavior equalities between matrices, for
a fixed input vector (vᵢ)ⁱ. It suffices to show same-behavior
equalities between each row of the matrices for this input
vector. We show that for any j,
- if Kₖ = Kᵥ for some Kₖ ∈ constrs(p₀ⱼ)ʲ, then
| (pᵢⱼ)ⁱ(vᵢ)ⁱ = rₖⱼ((v'ₗ)ˡ +++ tail(vᵢ)ⁱ
- otherwise
| (pᵢⱼ)ⁱ(vᵢ)ⁱ = rⱼ_{wild} tail(vᵢ)ⁱ
In the first case (Kᵥ is Kₖ for some Kₖ ∈ constrs(p₀ⱼ)ʲ), we
have to prove that
| (pᵢⱼ)ⁱ(vᵢ)ⁱ = rₖⱼ((v'ₗ)ˡ +++ tail(vᵢ)ⁱ
By definition of mₖ we know that rₖⱼ is equal to
| if pₒⱼ is Kₖ(qₗ) then
| \quad (qₗ)ˡ +++ tail(pᵢⱼ)ⁱ → eⱼ
| if pₒⱼ is _ then
| \quad (_)ˡ +++ tail(pᵢⱼ)ⁱ → eⱼ
| else ⊥
\begin{comment}
Maybe better as a table?
| pₒⱼ | rₖⱼ |
|--------+---------------------------|
| Kₖ(qₗ) | (qₗ)ˡ +++ tail(pᵢⱼ)ⁱ → eⱼ |
| _ | (_)ˡ +++ tail(pᵢⱼ)ⁱ → eⱼ |
| else | ⊥ |
\end{comment}
By definition of (pᵢ)ⁱ(vᵢ)ⁱ we know that (pᵢⱼ)ⁱ(vᵢ) is equal to
| (K(qⱼ)ʲ, tail(pᵢⱼ)ⁱ) (K(v'ₗ)ˡ,tail(vᵢ)ⁱ) := ((qⱼ)ʲ +++ tail(pᵢⱼ)ⁱ)((v'ₗ)ˡ +++ tail(vᵢ)ⁱ)
| (_, tail(pᵢⱼ)ⁱ) (vᵢ) := tail(pᵢⱼ)ⁱ(tail(vᵢ)ⁱ)
| (K(qⱼ)ʲ, tail(pᵢⱼ)ⁱ) (K'(v'ₗ)ˡ,tail(vⱼ)ʲ) := ⊥ if K ≠ K'
By definition, m(vᵢ)ⁱ is
| m(vᵢ)ⁱ = First(rⱼ(vᵢ)ⁱ)ʲ for m = ((aᵢ)ⁱ, (rⱼ)ʲ)
| (pᵢ)ⁱ (vᵢ)ⁱ = {
| \quad if p₀ = k(qₗ)ˡ, v₀ = k'(v'ₖ)ᵏ, k=Idx(k') and l=Idx(k)
| \quad \quad if k ≠ k' then ⊥
| if k = k' then ((qₗ)ˡ +++ (pᵢ)^{i∈I\DZ}) ((v'ₖ)ᵏ +++ (vᵢ)^{i∈I\DZ} )
| if p₀ = (q₁\vert{}q₂) then
| First( (q₁pᵢ^{i∈I\DZ}) vᵢ^{i∈I\DZ}, (q₂pᵢ^{i∈I \DZ}) vᵢ^{i∈I\DZ})}
We prove this first case by a second case analysis on p₀ⱼ.
For this reason, if we can prove that
| ∀j, rⱼ(vᵢ)ⁱ = r'ⱼ((v'ₖ)ᵏ ++ (vᵢ)ⁱ)
it follows that
| m(vᵢ)ⁱ = mₖ((v'ₖ)ᵏ ++ (vᵢ)ⁱ)
from the above definition.
TODO
We can also show that aᵢ = (a_{0.l})ˡ +++ a_{i∈I\DZ} because v(a₀) = K(v(a){0.l})ˡ)
In the second case (Kᵥ is distinct from Kₖ for all Kₖ ∈ constrs(pₒⱼ)ʲ),
we have to prove that
| (pᵢⱼ)ⁱ(vᵢ)ⁱ = rⱼ_{wild} tail(vᵢ)ⁱ
TODO
** Target translation
@ -436,7 +514,7 @@ respective decision tree produces the same result
The equivalence checking algorithm takes as input a domain of
possible values \emph{S} and a pair of source and target decision trees and
in case the two trees are not equivalent it returns a counter example.
The algorithm respects the following correctness statement:
Our algorithm respects the following correctness statement:
\begin{comment}
TODO: we have to define what \coversTEX mean for readers to understand the specifications
@ -554,14 +632,13 @@ We say that Cₜ covers the input space /S/, written
/covers(Cₜ, S)/ when every value vₛ∈S is a valid input to the
decision tree Cₜ. (TODO: rephrase)
Given an input space /S/ and a couple of decision trees, where
the target decision tree Cₜ covers the input space /S/, we say that
the two decision trees are equivalent when:
the target decision tree Cₜ covers the input space /S/ we can define equivalence:
| equiv(S, Cₛ, Cₜ, gs) = Yes ∧ covers(Cₜ, S) → ∀vₛ≃vₜ ∈ S, Cₛ(vₛ) ≃gs Cₜ(vₜ)
Similarly we say that a couple of decision trees in the presence of
an input space /S/ are /not/ equivalent when:
an input space /S/ are /not/ equivalent in the following way:
| equiv(S, Cₛ, Cₜ, gs) = No(vₛ,vₜ) ∧ covers(Cₜ, S) → vₛ≃vₜ ∈ S ∧ Cₛ(vₛ) ≠gs Cₜ(vₜ)
Corollary: For a full input space /S/, that is the universe of the
target program we say:
target program:
| equiv(S, 〚tₛ〛ₛ, 〚tₜ〛ₜ, ∅) = Yes ⇔ tₛ ≃ tₜ
@ -663,7 +740,7 @@ I think the unreachable case should go at the end.
3. When we have a Leaf or a Failure at the left side:
| equiv(S, Failure as Cₛ, Switch(a, (πᵢ → Cₜᵢ)^{i∈I})) := Forall(equiv( S∩a→π(kᵢ)), Cₛ, Cₜᵢ)^{i∈I})
| equiv(S, Leaf bbₛ as Cₛ, Switch(a, (πᵢ → Cₜᵢ)^{i∈I})) := Forall(equiv( S∩a→π(kᵢ)), Cₛ, Cₜᵢ)^{i∈I})
The algorithm either returns Yes for every sub-input space Sᵢ := S∩(a→π(kᵢ)) and
Our algorithm either returns Yes for every sub-input space Sᵢ := S∩(a→π(kᵢ)) and
subtree Cₜᵢ
| equiv(Sᵢ, Cₛ, Cₜᵢ) = Yes ∀i
or we have a counter example vₛ, vₜ for which
@ -676,7 +753,7 @@ I think the unreachable case should go at the end.
4. When we have a Switch on the right we define π_{fallback} as the domain of
values not covered but the union of the constructors kᵢ
| π_{fallback} = ¬\bigcup\limits_{i∈I}π(kᵢ)
The algorithm proceeds by trimming
Our algorithm proceeds by trimming
| equiv(S, Switch(a, (kᵢ → Cₛᵢ)^{i∈I}, C_{sf}), Cₜ) :=
| Forall(equiv( S∩(a→π(kᵢ)^{i∈I}), Cₛᵢ, C_{t/a→π(kᵢ)})^{i∈I} +++ equiv(S∩(a→πₙ), Cₛ, C_{a→π_{fallback}}))
The statement still holds and we show this by first analyzing the