paper: simplify pseudo grammar
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paper/main.tex
162
paper/main.tex
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@ -1,4 +1,4 @@
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\documentclass[10pt, nonacm]{acmart}
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\documentclass[10pt, sigplan, nonacm]{acmart}
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\usepackage[utf8]{inputenc}
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\usepackage{formal-grammar}
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@ -73,151 +73,139 @@ which are already known from SystemF,
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types can be of the form \(\tau_1 \sim \tau_2\) to denote a \emph{ladder type} to formalizes the notion of a type \(\tau_1\) being represented in terms of type \(\tau_2\).
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Similar to SystemF, expressions can be \emph{variables}, \emph{type-abstractions}, \emph{}
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Coq definitions of the abstract syntax can be found in \hyperref[coq:terms]{\texttt{terms.v}}.
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\begin{figure}[h]
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\label{gr:core}
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\begin{grammar}
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\firstcase{ T_\seltype \textsf{$(\typenames, \typevars)$} }{
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\firstcase{ T }{
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\metavariable{\sigma}
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}{Type Literal \quad \textsf{where $ \metavariable{\sigma} \in \typenames $}}
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}{Base Type}
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\otherform{
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\metavariable{\alpha}
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}{Type Variable \quad \textsf{where $ \metavariable{\alpha} \in \typevars $}}
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}{Type Variable}
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\otherform{
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$$\typeterminal{\forall}$$ \metavariable{\alpha} \typeterminal{.} \quad \typenonterm{\typevars \cup \{\metavariable{\alpha}\}}
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\typeterminal{\forall} \metavariable{\alpha} \typeterminal{.} \nonterm{T}
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}{Universal Type}
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\otherform{
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\typeterminal{<} \typenonterm{\typevars} \quad \typenonterm{\typevars} \typeterminal{>}
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}{Specialization}
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\typeterminal{<} \nonterm{T} \quad \nonterm{T} \typeterminal{>}
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}{Specialized Type}
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\otherform{
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\typenonterm{\typevars}
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\quad $$\typeterminal{\rightarrow}$$ \quad
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\typenonterm{\typevars}
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\nonterm{T} \quad \typeterminal{\rightarrow} \quad \nonterm{T}
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}{Function Type}
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\otherform{
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\typenonterm{\typevars}
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\quad $$\typeterminal{\rightarrow_{morph}}$$ \quad
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\typenonterm{\typevars}
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\nonterm{T} \quad \typeterminal{\rightarrow_\text{morph}} \quad \nonterm{T}
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}{Morphism Type}
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\otherform{
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\typenonterm{\typevars}
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\quad $$\typeterminal{\sim}$$ \quad
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\typenonterm{\typevars}
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\nonterm{T} \quad \typeterminal{\sim} \quad \nonterm{T}
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}{Ladder Type}
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\otherform{
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$$\typeterminal{(}$$ \quad
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\typenonterm{\typevars}
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\quad $$\typeterminal{)}$$
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}{Parenthesis}
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$$\\$$
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\firstcase{ T_\selexpr \textsc{$(\typenames, \typevars, \exprvars)$} }
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\firstcase{ E
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% T_\selexpr
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}
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{ \metavariable{x}
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} {Variable \quad \textsf{where $\metavariable{x} \in \exprvars$} }
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} {Variable}
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\otherform{
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$$ \exprterminal{\Lambda} \metavariable{\alpha}
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\quad \exprterminal{\mapsto} \quad $$
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\exprnonterm{\typevars \cup \{\metavariable{\alpha}\}}{\exprvars}
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\nonterm{ E }
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}{Type Abstraction}
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\otherform{
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$$ \exprterminal{\lambda} \metavariable{x} $$
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\exprterminal{:} \typenonterm{\typevars}
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\exprterminal{:} \nonterm{ T }
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\quad $$\exprterminal{\mapsto}$$ \quad
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\exprnonterm{\typevars}{\exprvars \cup \{\metavariable{x}\}}
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\nonterm{ E }
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}{Value Abstraction}
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\otherform{
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$$ \exprterminal{\lambda} \metavariable{x} $$
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\exprterminal{:} \typenonterm{\typevars}
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\quad $$\exprterminal{\mapsto_{morph}}$$ \quad
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\exprnonterm{\typevars}{\exprvars \cup \{\metavariable{x}\}}
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\exprterminal{:} \nonterm{ T }
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\quad $$\exprterminal{\mapsto_\text{morph}}$$ \quad
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\nonterm{ E }
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}{Value Morphism}
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\otherform{
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\exprterminal{let} \quad \metavariable{x} \quad \exprterminal{=} \quad
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\exprnonterm{\typevars}{\exprvars}
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\nonterm{ E }
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\quad \exprterminal{in} \quad
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\exprnonterm{\typevars}{\exprvars \cup \{\metavariable{x}\}}
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\nonterm{ E }
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}{Variable Binding}
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\otherform{
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\exprnonterm{\typevars}{\exprvars}
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\nonterm{ E }
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\quad
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\typenonterm{\typevars}
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\nonterm{ T }
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}{Type Application}
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\otherform{
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\exprnonterm{\typevars}{\exprvars}
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\nonterm{ E }
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\quad
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\exprnonterm{\typevars}{\exprvars}
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\nonterm{ E }
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}{Value Application}
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\otherform{
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\exprnonterm{\typevars}{\exprvars}
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\nonterm{ E }
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\quad
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\exprterminal{as}
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\quad
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\typenonterm{\typevars}
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}{Type Cast}
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\nonterm{ T }
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}{Up-Cast}
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\otherform{
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\exprterminal{(} \quad
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\exprnonterm{\typevars}{\exprvars}
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\quad \exprterminal{)}
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}{Parenthesis}
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\nonterm{ E }
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\quad
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\exprterminal{to}
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\quad
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\nonterm{ T }
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}{Transformation}
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\otherform{\exprterminal{(} \quad \nonterm{E} \quad \exprterminal{)}}{Parenthesis}
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$$\\$$
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\firstcase{ T_\textsc{Val} \textsc{$(\typenames, \typevars, \exprvars)$} }{
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\firstcase{V}{
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\exprterminal{\epsilon}
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}{Empty Value}
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\otherform{
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\metavariable{x} \quad \valnonterm{\typevars}{\exprvars}
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}{Value Conactenation}
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\otherform{
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\exprterminal{\Lambda} \metavariable{\alpha} \quad
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\exprterminal{\mapsto} \quad
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\valnonterm{ \typevars \cup \{ \metavariable{\alpha} \} }
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\{Type-Function Value}
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\nonterm{ V }
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}{Type-Abstraction Value}
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\otherform{
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\exprterminal{\lambda} \metavariable{x} \quad
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\exprterminal{:} \quad
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\typenonterm{\emptyset} \quad
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\exprterminal{\lambda} \metavariable{x}
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\exprterminal{:}
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\nonterm{ T } \quad
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\exprterminal{\mapsto} \quad
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\exprnonterm{\typevars}{\{\metavariable{x}\}}
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}{Function Value}
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\nonterm{ E }
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}{Abstraction Value}
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\otherform{
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\valnonterm{ \typevars } \quad
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\nonterm{ V } \quad
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\exprterminal{as} \quad
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\typenonterm{ \typevars }
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}{Value}
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\nonterm{ T }
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}{Cast Value}
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\end{grammar}
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\caption{Syntax of the core calculus with colors for \metavariable{metavariables}, \typeterminal{type-level terminal symbols}, \exprterminal{expression-level terminal symbols}
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where $\typenames, \typevars, \exprvars$ are mutually disjoint, countable sets of symbols to denote atomic type identifiers (\(\typenames\)), free typevariables (\(\typevars\)), and free expression variables (\(\exprvars\)).
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where $\typenames, \typevars, \exprvars$ are mutually disjoint, countable sets of symbols to denote atomic type identifiers (\(\typenames\)), typevariables (\(\typevars\)), and expression variables (\(\exprvars\)).
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By default, assume \(\metavariable{\sigma} \in \typenames\), \(\metavariable{\alpha} \in \typevars\) and \(\metavariable{x} \in \exprvars\)
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$$\\$$}
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\end{figure}
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@ -228,25 +216,25 @@ Let \(\Sigma = \{ \text{Digit}, \text{Char}, \text{Seq}, \text{UTF-8}, \mathbb{N
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The following terms are valid types over \(\Sigma\):
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\begin{enumerate}
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\item \typeterminal{<Seq Char>} \( \in \typenonterm{\emptyset}\)\\
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\item \typeterminal{<Seq Char>}\\ %\( \in \typenonterm{\emptyset}\)\\
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"sequence of characters"
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\item \typeterminal{<Seq <Digit 10> \(\sim\) Char>} \( \in \typenonterm{\emptyset}\)\\
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\item \typeterminal{<Seq <Digit 10> \(\sim\) Char>}\\ %\( \in \typenonterm{\emptyset}\)\\
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"sequence of decimal digits, where each digit is represented as character"
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\item \typeterminal{<Seq Item> \(\rightarrow \mathbb{N} \rightarrow\) Item} \( \in \typenonterm{\{Item\}}\)\\
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\item \typeterminal{<Seq Item> \(\rightarrow \mathbb{N} \rightarrow\) Item}\\ %\( \in \typenonterm{\{Item\}}\)\\
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"function that maps a sequence of items and a natural number to an item"\\
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Note: this type contains the free variable \typeterminal{Item}
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\item \typeterminal{<Seq Char> \(\sim\) UTF-8 \(\rightarrow \mathbb{N} \rightarrow\) Char } \( \in \typenonterm{\emptyset}\)\\
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%Note: this type contains the free variable \typeterminal{Item}
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\item \typeterminal{<Seq Char> \(\sim\) UTF-8 \(\rightarrow \mathbb{N} \rightarrow\) Char }\\ %\( \in \typenonterm{\emptyset}\)\\
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"function that takes a sequence of chars, represented as UTF-8 string, and a natural number to return a character"
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\item \typeterminal{\(\forall\) Radix . <Seq <Digit Radix> \(\sim\) Char>} \(\in \typenonterm{\emptyset} \)\\
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"given the parameter \typeterminal{Radix}, a sequence of digits where each digit is represented as character"\\
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Note: this type-term is \emph{ground} (i.e. \(\typevars = \emptyset\)), since \typeterminal{Radix} is bound by \(\typeterminal{\forall}\)
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\item \typeterminal{\(\forall\) Radix . <Seq <Digit Radix> \(\sim\) Char>}\\ %\(\in \typenonterm{\emptyset} \)\\
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"given the parameter \typeterminal{Radix}, a sequence of digits where each digit is represented as character"
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%Note: this type-term is \emph{ground} (i.e. \(\typevars = \emptyset\)), since \typeterminal{Radix} is bound by \(\typeterminal{\forall}\)
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\item \typeterminal{
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\(\forall\) SrcRadix.\\
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\(\forall\) DstRadix.\\
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\(\mathbb{N} \sim\) <PosInt SrcRadix> \(\sim\) <Seq <Digit SrcRadix> \(\sim\) Char>\\
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\(\rightarrow_{morph}\)\\
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\(\mathbb{N} \sim\) <PosInt DstRadix> \(\sim\) <Seq <Digit DstRadix> \(\sim\) Char>\\
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} \(\in \typenonterm{\emptyset} \)\\
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}\\ %\(\in \typenonterm{\emptyset} \)\\
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"morphism function that maps the \typeterminal{PosInt} representation of \(\typeterminal{\mathbb{N}}\) with radix \typeterminal{SrcRadix} to the \typeterminal{PosInt} representation of radix \typeterminal{DstRadix}"
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\end{enumerate}
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\end{example}
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@ -254,8 +242,10 @@ Note: this type-term is \emph{ground} (i.e. \(\typevars = \emptyset\)), since \t
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\begin{definition}[Substitution in Types]
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Given a type-variable assignment \(\psi_t = \{ \metavariable{\alpha_1} \mapsto \metavariable{\tau_1}, \quad \metavariable{\alpha_2} \mapsto \metavariable{\tau_2}, \quad \dots \}\),
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the thereby induced, lexically scoped substitution \(\overline{\psi_t}\) replaces all \emph{free} occurences of the variables \(\metavariable{\alpha_i}\) in a type-term \(\metavariable{\xi} \in \typenonterm{\{\metavariable{\alpha_1}, \quad \metavariable{\alpha_2}, \quad \dots\}}\) recursively with the type-term given by \(\psi_t(\metavariable{\alpha_i})\).
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Lexical scoping is implemented by simply not substituting any bound occourences of variables \(\metavariable{\alpha_i}\). This allows to skip \(\alpha\)-conversion as done in classical \(\lambda\)-calculus.
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the thereby induced, substitution \(\overline{\psi_t}\) replaces all \emph{free} occurences of the variables \(\metavariable{\alpha_i}\) in a type-term \(\metavariable{\xi} \in \typenonterm{\{\metavariable{\alpha_1}, \quad \metavariable{\alpha_2}, \quad \dots\}}\) recursively with the type-term given by \(\psi_t(\metavariable{\alpha_i})\).
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Occourences of bound variables \(\metavariable{\alpha_i}\) are
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Coq definition is at \hyperref[coq:subst-type]{subst.v:\ref{coq:subst-type}}.
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\[\overline{\psi_t} \metavariable{\xi} = \begin{cases}
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\metavariable{\xi} \quad \text{if } \metavariable{\xi} \in \typenames\\
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@ -369,7 +359,7 @@ As usual, each rule is composed of premises (above the horizontal line) and a co
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\inferrule[T-Variable]{
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\metavariable{x} \in \exprvars\\
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\metavariable{\tau} \in \typenonterm{\emptyset}\\
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\metavariable{\tau} \in \nonterm{T}\\
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\metavariable{x}:\metavariable{\tau} \in \Gamma\\
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}{
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\Gamma \vdash \metavariable{x}:\metavariable{\tau}
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@ -385,25 +375,25 @@ As usual, each rule is composed of premises (above the horizontal line) and a co
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\inferrule[T-TypeAbs]{
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\metavariable{\tau} \in \typenonterm{\typevars \cup \{\metavariable{\alpha}\}} \\
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\metavariable{e} \in \exprnonterm{\typevars \cup \{ \metavariable{\alpha} \}}{\exprvars} \\
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\metavariable{\tau} \in \nonterm{T} \\
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\metavariable{e} \in \nonterm{E} \\
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\Gamma \vdash \metavariable{e} : \metavariable{\tau} \\
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}{
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\Gamma \vdash (\exprterminal{\Lambda} \metavariable{\alpha} \exprterminal{\mapsto} \metavariable{e}) : \typeterminal{\forall}\metavariable{\alpha}\typeterminal{.}\metavariable{\tau}
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}
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\inferrule[T-TypeApp]{
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\metavariable{\tau} \in \typenonterm{\typevars \cup \{\metavariable{\alpha}\}} \\
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\metavariable{\tau} \in \nonterm{T} \\
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\Gamma \vdash \metavariable{e} : \typeterminal{\forall} \metavariable{\alpha} \typeterminal{.} \metavariable{\tau} \\
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\metavariable{\sigma} \in \typenonterm{\typevars}
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\metavariable{\sigma} \in \nonterm{T}
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}{
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\Gamma \vdash ( \metavariable{e} \quad \metavariable{\sigma} ) : \{\metavariable{\alpha} \mapsto \metavariable{\sigma}\} \metavariable{\tau}
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}
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\inferrule[T-ValueAbs]{
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\metavariable{\sigma}, \metavariable{\tau} \in \typenonterm{\typevars} \\
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\metavariable{e} \in \exprnonterm{\typevars}{\exprvars \cup \{ \metavariable{x} \} } \\
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\metavariable{\sigma}, \metavariable{\tau} \in \nonterm{T} \\
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\metavariable{e} \in \nonterm{E} \\
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\Gamma \vdash \metavariable{e} : \metavariable{\tau} \\
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}{
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\Gamma \vdash (\exprterminal{\lambda} \metavariable{x} \exprterminal{:} \metavariable{\sigma} \exprterminal{\mapsto} \metavariable{e}) : \metavariable{\sigma}\typeterminal{\rightarrow}\metavariable{\tau}
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@ -424,8 +414,8 @@ As usual, each rule is composed of premises (above the horizontal line) and a co
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}\and
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\inferrule[T-MorphAbs]{
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\metavariable{\sigma}, \metavariable{\tau} \in \typenonterm{\typevars} \\
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\metavariable{e} \in \exprnonterm{\typevars}{\exprvars \cup \{ \metavariable{x} \} } \\
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\metavariable{\sigma}, \metavariable{\tau} \in \nonterm{T} \\
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\metavariable{e} \in \nonterm{E} \\
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\Gamma \vdash \metavariable{e} : \metavariable{\tau} \\
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}{
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\Gamma \vdash (\exprterminal{\lambda} \metavariable{x} \exprterminal{:} \metavariable{\tau} \exprterminal{\mapsto_{morph}} \metavariable{e}) : \metavariable{\sigma}\typeterminal{\rightarrow_{morph}}\metavariable{\tau}
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@ -457,7 +447,7 @@ As usual, each rule is composed of premises (above the horizontal line) and a co
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\end{definition}
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\subsection{Evaluation Semantics}
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\subsection{Evaluation}
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Evaluation of an expression \(\metavariable{e} \in \exprnonterm{\emptyset}{\emptyset}\) is defined by exhaustive application of the rewrite rules \(\rightarrow_\beta\) and \(\rightarrow_\delta\),
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which are given in \ref{def:evalrules}.
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@ -559,7 +549,7 @@ Then \(\emptyset \vdash \metavariable{e'} : \metavariable{\tau}\)
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\end{lemma}
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\subsection{Proof of Syntactic Type Soundness}
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\subsection{Soundness}
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\begin{lemma}[\(\beta\)-Preservation]
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\label{lemma:beta-preservation}
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