Juno Frontend

• The initial implementation of the Juno Frontend
• A substantial portion of the Juno language is implemented, most outstanding features are related to match statements, modules, and type inference
• A handful of examples are present in juno_frontend/examples, including a version of CAVA though it does not compile as it depends on a number of features that are yet to be implemented.

frontend/spec.tex

-\documentclass[letterpaper]{article}
-\usepackage[utf8]{inputenc}
-\usepackage[top=1in,right=1in,left=1in,bottom=1in]{geometry}
-\usepackage{amsfonts}
-\usepackage{amsmath}
-\usepackage{amssymb}
-\usepackage{amsthm}
-\usepackage[english]{babel}
-\usepackage{fancyhdr}
-\usepackage{xcolor}
-\usepackage{comment}
-\usepackage{hyperref}
-\hypersetup{
-    colorlinks=true,
-    linkcolor=black,
-    filecolor=magenta,      
-    urlcolor=cyan
-    }
-
-\usepackage[inference]{semantic}
-\usepackage{textcomp}
-\usepackage{listings}
-% Don't change, used for formatting regular expressions
-\lstset{basicstyle=\ttfamily, upquote=true}
-
-\allowdisplaybreaks
-
-\pagestyle{fancy}
-\fancyhf{}
-\chead{}
-\rhead{Front-End Spec}
-\lhead{DRAFT: 2024-01-09}
-
-\renewcommand{\footrulewidth}{1pt}
-\rfoot{\thepage}
-
-\title{Hercules Front-End Spec (Name TBD) \\ \large Language Specification}
-\author{Aaron Councilman, Russel Arbore}
-\date{January 9, 2024}
-
-\newcommand{\nonterminal}[1]{#1\ }
-\newcommand{\terminal}[1]{\text{`#1'}\ }
-\newcommand{\regex}[1]{\text{\lstinline$/#1/$}\ }
-
-\newcommand{\gramOption}[1]{[\ #1]\ }
-\newcommand*{\gramRepeat}[2][]{\{\ #2\}_{#1}\ }
-\newcommand*{\gramSome}[2][]{\{\ #2\}^{+}_{#1}\ }
-\newcommand{\gramOr}{\mid\ }
-
-\begin{document}
-\maketitle
-
-This document gives the formal specification of the Hercules front-end language.
-Section~\ref{sec:overview} provides an informal overview of the language: its features and notable differences from other languages.
-The formal description of the language is contained in Section~\ref{sec:syntax} which defines the syntax, Section~\ref{sec:types} which defines the type-system and semantic analysis rules, and Section~\ref{sec:semantics} which defines the formal semantics.
-
-\section{Overview}\label{sec:overview}
-TODO
-
-\section{Syntax}\label{sec:syntax}
-The grammar below is provided in an Extended Backus-Naur form.
-In particular, concatenation is represented by whitespace between grammar symbols, terminals are represented in single quotes for literal strings as $\terminal{terminal}$ or surrounded by slashes for regular expressions as $\regex{regex}$ while nonterminals are non-quoted and italicized as $\nonterminal{nonterminal}$.
-Certain other symbols have meta meanings \emph{when not quoted within a terminal}, specifically parentheses $(\cdots)$ are used for grouping, square brackets $[\cdots]$ indicate an optional component, and curly brackets $\{ \cdots \}$ indicate repetition of zero or more occurrences.
-Curly brackets with a symbol in subscript indicates a list of zero or more occurrences separated by the symbol, for instance $\gramRepeat[\terminal{,}]{\nonterminal{Nt}}$ represents the empty string, a single nonterminal $\nonterminal{Nt}$, or a list of multiple $\nonterminal{Nt}$ separated by commas.
-A curly bracket with a plus symbol in the superscript (with or without subscript) indicates at least repetition, as in $\{ \cdots \}^{+}$.
-The vertical bar symbol $\mid$ indicates alternatives and epsilon $\varepsilon$ indicates the empty string.
-
-The language is whitespace insensitive and resolves lexing ambiguities by maximal munch.
-The language also supports C/C++ style line comments and block comments, allowing arbitrary nesting of the latter.
-
-\begin{align*}
-%  
-  \nonterminal{Program} ::&= \gramRepeat{\nonterminal{Top}} \\
-%
-  \nonterminal{Top} ::&= \nonterminal{Import}
-    \gramOr \nonterminal{TypeDecl}
-    \gramOr \nonterminal{ConstDecl}
-    \gramOr \nonterminal{FuncDecl}
-    \gramOr \nonterminal{Module} \\
-%
-  \nonterminal{Module} ::&=
-    \gramOption{\terminal{pub}} \terminal{module} \nonterminal {Id}
-      \terminal{\{} \gramRepeat{\nonterminal{Top}} \terminal{\}} \\
-%
-  \nonterminal{Import} ::&=
-    \terminal{use} \nonterminal{PackageId} \terminal{;} \\
-%
-  \nonterminal{PackageId} ::&=
-    \nonterminal{PackageName} \gramOption{\terminal{::} \terminal{*}} \\
-%
-  \nonterminal{PackageName} ::&= \gramSome[\terminal{::}]{\nonterminal{Id}} \\
-%
-  \nonterminal{TypeDecl} ::&=
-    \gramOption{\terminal{pub}} \terminal{type} \nonterminal{Id}
-      \gramOption{\terminal{\textless}
-        \gramRepeat[\terminal{,}]{\nonterminal{TypeVar}} \terminal{\textgreater}}
-      \terminal{=} \nonterminal{TypeDef} \terminal{;} \\
-%
-  \nonterminal{TypeDef} ::&= \nonterminal{Type}
-    \gramOr \gramOption{\terminal{pub}} \terminal{struct}
-      \terminal{\{} \gramRepeat{\nonterminal{ObjField}} \terminal{\}} \\
-    &\gramOr \gramOption{\terminal{pub}} \terminal{union}
-      \terminal{\{} \gramRepeat{\nonterminal{ObjField}} \terminal{\}} \\
-%
-  \nonterminal{ObjField} ::&=
-    \gramOption{\terminal{pub}} \nonterminal{Id}
-      \gramOption{\terminal{:} \nonterminal{Type}} \terminal{;} \\
-%
-  \nonterminal{TypeVar} ::&= \nonterminal{Id}
-    \gramOr \nonterminal{Id} \terminal{:} \nonterminal{Kind} \\
-%
-  \nonterminal{Kind} ::&= \terminal{type} \gramOr \terminal{usize}
-    \gramOr \terminal{bool} \gramOr \terminal{number} \gramOr \terminal{integer} \\
-%
-  \nonterminal{Type} ::&= \nonterminal{PrimType}
-    \gramOr \terminal{(} \gramRepeat[\terminal{,}]{\nonterminal{Type}} \terminal{)} \\
-    &\gramOr \nonterminal{PackageName}
-      \gramOption{\terminal{\textless}
-        \gramRepeat[\terminal{,}]{\nonterminal{TypeExpr}} \terminal{\textgreater}}
-    \gramOr \nonterminal{Type}
-      \terminal{[} \gramRepeat[\terminal{,}]{\nonterminal{TypeExpr}} \terminal{]} \\
-%
-  \nonterminal{ConstDecl} ::&= \gramOption{\terminal{pub}}
-    \terminal{const} \nonterminal{Id} \gramOption{\terminal{:} \nonterminal{Type}}
-    \terminal{=} \nonterminal{Expr} \terminal{;} \\
-%
-  \nonterminal{FuncDecl} ::&=
-    \gramOption{\nonterminal{FuncAttr}}
-    \gramOption{\terminal{pub}} \terminal{fn} \nonterminal{Id}
-      \gramOption{\terminal{\textless}
-        \gramRepeat[\terminal{,}]{\nonterminal{TypeVar}} \terminal{\textgreater}} \\
-    &\hspace{.5cm}
-      \terminal{(} \gramRepeat[\terminal{,}]{\gramOption{\terminal{inout}}
-        \nonterminal{VarBinding}} \terminal{)}
-      \gramOption{\terminal{:} \nonterminal{Type}} \nonterminal{Stmts} \\
-%
-  \nonterminal{FuncAttr} ::&= \regex{#\\[[^\\]]*\\]} \\
-%
-  \nonterminal{VarBinding} ::&= \nonterminal{SPattern} \gramOption{\terminal{:} \nonterminal{Type}} \\
-%
-  \nonterminal{Stmt} ::&=
-    \terminal{let} \nonterminal{VarBinding}
-      \gramOption{\terminal{=} \nonterminal{Expr}} \terminal{;}
-     \gramOr \terminal{const} \nonterminal{VarBinding}
-      \terminal{=} \nonterminal{Expr} \terminal{;} \\
-    &\gramOr \nonterminal{LExpr} \terminal{=} \nonterminal{Expr} \terminal{;}
-     \gramOr \nonterminal{LExpr} \terminal{+=} \nonterminal{Expr} \terminal{;}
-     \gramOr \nonterminal{LExpr} \terminal{-=} \nonterminal{Expr} \terminal{;} \\
-    &\gramOr \nonterminal{LExpr} \terminal{*=} \nonterminal{Expr} \terminal{;}
-     \gramOr \nonterminal{LExpr} \terminal{/=} \nonterminal{Expr} \terminal{;}
-     \gramOr \nonterminal{LExpr} \terminal{\%=} \nonterminal{Expr} \terminal{;} \\
-    &\gramOr \nonterminal{LExpr} \terminal{\&=} \nonterminal{Expr} \terminal{;}
-     \gramOr \nonterminal{LExpr} \terminal{\textbar=} \nonterminal{Expr} \terminal{;}
-     \gramOr \nonterminal{LExpr} \terminal{\^{}=} \nonterminal{Expr} \terminal{;} \\
-    &\gramOr \nonterminal{LExpr} \terminal{\&\&=} \nonterminal{Expr} \terminal{;}
-     \gramOr \nonterminal{LExpr} \terminal{\textbar\textbar=} \nonterminal{Expr} \terminal{;} \\
-    &\gramOr \nonterminal{LExpr} \terminal{\textless\textless=} \nonterminal{Expr} \terminal{;}
-     \gramOr \nonterminal{LExpr} \terminal{\textgreater\textgreater=} \nonterminal{Expr} \terminal{;} \\
-    &\gramOr \terminal{if} \nonterminal{Expr} \nonterminal{Stmts}
-      \gramOption{\terminal{else} \nonterminal{Stmts}} \\
-    &\gramOr \terminal{match} \nonterminal{Expr} \nonterminal{Cases} \\
-    &\gramOr \terminal{for}
-      \nonterminal{VarBinding} \terminal{=} \nonterminal{Expr}
-      \terminal{to} \nonterminal{Expr}
-      \gramOption{\terminal{by} \nonterminal{Expr}} \nonterminal{Stmts} \\
-    &\gramOr \terminal{while} \nonterminal{Expr} \nonterminal{Stmts} \\
-    &\gramOr \terminal{return} \nonterminal{Expr} \terminal{;} \\
-    &\gramOr \terminal{break} \terminal{;}
-     \gramOr \terminal{continue} \terminal{;}
-     \gramOr \nonterminal{Stmts} \\
-    &\gramOr \nonterminal{PackageName}
-      \gramOption{\terminal{::} \terminal{\textless}
-        \gramRepeat[\terminal{,}]{\nonterminal{TypeExpr}} \terminal{\textgreater}}
-      \terminal{(} \gramRepeat[\terminal{,}]{\gramOption{\terminal{\&}} \nonterminal{Expr}} \terminal{)} \terminal{;} \\
-%
-  \nonterminal{Stmts} ::&=
-    \terminal{\{} \gramRepeat{\nonterminal{Stmt}} \terminal{\}} \\
-%
-  \nonterminal{Cases} ::&=
-    \terminal{\{} \gramRepeat{\nonterminal{Case}} \terminal{\}} \\
-%
-  \nonterminal{Case} ::&=
-    \nonterminal{Patterns} \terminal{=\textgreater} \nonterminal{Stmt} \\
-%
-  \nonterminal{Patterns} ::&=
-    \gramOption{\terminal{\textbar}}
-      \gramSome[\terminal{\textbar}]{\nonterminal{Pattern}} \\
-%
-  \nonterminal{Pattern} ::&= \nonterminal{SPattern}
-    \gramOr \nonterminal{PackageName} \nonterminal{SPattern} \\
-%
-  \nonterminal{SPattern} ::&= \terminal{\textunderscore}
-    \gramOr \nonterminal{IntLit} \gramOr \nonterminal{PackageName}
-    \gramOr \terminal{(} \gramRepeat[\terminal{,}]{\nonterminal{Pattern}} \terminal{)}
-    \gramOr \terminal{\{} \gramRepeat[\terminal{,}]{\nonterminal{Pattern}} \terminal{\}} \\
-    &\gramOr \terminal{\{}
-      \gramRepeat[\terminal{,}]{\nonterminal{Id} \terminal{=} \nonterminal{Pattern}} \terminal{\}} \\
-%
-  \nonterminal{LExpr} ::&= \nonterminal{Id}
-    \gramOr \nonterminal{LExpr} \terminal{.} \nonterminal{Id}
-    \gramOr \nonterminal{LExpr} \regex{\\.[0-9]+}
-    \gramOr \nonterminal{LExpr} \terminal{[} \gramRepeat[\terminal{,}]{\nonterminal{Expr}} \terminal{]} \\
-%
-  \nonterminal{Expr} ::&= \nonterminal{PackageName}
-    \gramOr \nonterminal{Expr} \terminal{.} \nonterminal{Id}
-    \gramOr \nonterminal{Expr} \regex{\\.[0-9]+} \\
-   &\gramOr \nonterminal{Expr} \terminal{[} \gramRepeat[\terminal{,}]{\nonterminal{Expr}} \terminal{]}
-    \gramOr \terminal{(} \gramRepeat[\terminal{,}]{\nonterminal{Expr}} \terminal{)}
-    \gramOr \terminal{\{} \gramRepeat[\terminal{,}]{\nonterminal{Expr}} \terminal{\}} \\
-   &\gramOr \terminal{\{}
-      \gramRepeat[\terminal{,}]{\nonterminal{Id} \terminal{=} \nonterminal{Expr}} \terminal{\}} \\
-    &\gramOr \nonterminal{BoolLit} \gramOr \nonterminal{IntLit} \gramOr \nonterminal{FloatLit}
-     \gramOr \terminal{-} \nonterminal{Expr}
-     \gramOr \terminal{\texttildelow} \nonterminal{Expr}
-     \gramOr \terminal{!} \nonterminal{Expr} \\
-    &\gramOr \nonterminal{Expr} \terminal{as} \nonterminal{Type} \\
-    &\gramOr \nonterminal{Expr} \terminal{+} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{-} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{*} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{/} \nonterminal{Expr} \\
-    &\gramOr \nonterminal{Expr} \terminal{\%} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{\&} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{\textbar} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{\^{}} \nonterminal{Expr} \\
-    &\gramOr \nonterminal{Expr} \terminal{\&\&} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{\textbar\textbar} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{\textless} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{\textless=} \nonterminal{Expr} \\
-    &\gramOr \nonterminal{Expr} \terminal{\textgreater} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{\textgreater=} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{==} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{!=} \nonterminal{Expr} \\
-    &\gramOr \nonterminal{Expr} \terminal{\textless\textless} \nonterminal{Expr}
-     \gramOr \nonterminal{Expr} \terminal{\textgreater\textgreater} \nonterminal{Expr} \\
-    &\gramOr \terminal{if} \nonterminal{Expr} \terminal{then} \nonterminal{Expr}
-             \terminal{else} \nonterminal{Expr} \\
-    &\gramOr \nonterminal{PackageName}
-      \gramOption{\terminal{::} \terminal{\textless}
-        \gramRepeat[\terminal{,}]{\nonterminal{TypeExpr}} \terminal{\textgreater}}
-      \terminal{(} \gramRepeat[\terminal{,}]{\gramOption{\terminal{\&}} \nonterminal{Expr}} \terminal{)} \\
-%
-\nonterminal{TypeExpr} ::&= \nonterminal{PrimType}
-  \gramOr \terminal{(} \gramRepeat[\terminal{,}]{\nonterminal{TypeExpr}} \terminal{)} \\
-  &\gramOr \nonterminal{PackageName} \gramOption{\terminal{\textless} \gramRepeat[\terminal{,}]{\nonterminal{TypeExpr}} \terminal{\textgreater}}
-  \gramOr \nonterminal{TypeExpr} \terminal{[} \gramRepeat[\terminal{,}]{\nonterminal{Expr}} \terminal{]} \\
-  &\gramOr \nonterminal{PackageName} 
-   \gramOr \nonterminal{BoolLit} \gramOr \nonterminal{IntLit} \gramOr \nonterminal{FloatLit}
-   \gramOr \terminal{-} \nonterminal{TypeExpr} \\
-  &\gramOr \nonterminal{TypeExpr} \terminal{+} \nonterminal{TypeExpr}
-   \gramOr \nonterminal{TypeExpr} \terminal{-} \nonterminal{TypeExpr} \\
-  &\gramOr \nonterminal{TypeExpr} \terminal{*} \nonterminal{TypeExpr}
-   \gramOr \nonterminal{TypeExpr} \terminal{as} \nonterminal{Type} \\
-%
-  \nonterminal{PrimType} ::&= \terminal{bool}
-    \gramOr \terminal{i8} \gramOr \terminal{u8}
-    \gramOr \terminal{i16} \gramOr \terminal{u16}
-    \gramOr \terminal{i32} \gramOr \terminal{u32}
-    \gramOr \terminal{i64} \gramOr \terminal{u64} \\
-    &\gramOr \terminal{usize} \gramOr \terminal{f32} \gramOr \terminal{f64} \gramOr \terminal{void} \\
-%
-  \nonterminal{Id} ::&= \regex{[a-zA-Z][a-zA-Z0-9_]*} \\
-%
-  \nonterminal{BoolLit} ::&= \terminal{true} \gramOr \terminal{false} \\
-%
-  \nonterminal{IntLit} ::&= \regex{[0-9]+} \gramOr \regex{0x[0-9a-fA-F]+}
-    \gramOr \regex{0b[0-1]+} \gramOr \regex{0o[0-7]+} \\
-%
-  \nonterminal{FloatLit} ::&= \regex{[0-9]+\\.[0-9]*(e[0-9]+)?} \\
-\end{align*}
-%
-The grammar specified is ambiguous in a few places, the details of the disambiguation are provided below:
-\begin{enumerate}
-  \item All keywords (defined below) are reserved and are not parsed as members of the $\nonterminal{Id}$ nonterminal.
-  \item The grammar experience dangling else ambiguity, which is resolved by attaching the else to nearest if.
-  \item For conditional in expressions, the expression following the `else' captures as much as possible.
-  \item The unary and binary operators produce significant ambiguity.
-    This is resolved though associativities and precedences, listed below.
-    In this list, the top of the list are the operators which bind most tightly.
-    \begin{enumerate}
-      \item Left associative: `.', (dot number), `[]'
-      \item Right associative: `-' (unary), `\texttildelow', `!', and `\&' (unary)
-      \item Left associative: `as' and `size'
-      \item Left associative: `*', `/', and `\%'
-      \item Left associative: `+' and `-' (binary)
-      \item Left associative: `\textless\textless', and `\textgreater\textgreater'
-      \item Non associative: `\textless', `\textless=', `\textgreater', `\textgreater='
-      \item Non associative: `==' and `!='
-      \item Left associative: `\&' (binary)
-      \item Left associative: `\^{}'
-      \item Left associative: `\textbar'
-      \item Left associative: `\&\&'
-      \item Left associative: `\textbar\textbar'
-      \item Non associative: `if' $\cdots$ `then' $\cdots$ `else' $\cdots$
-      \item Non associative: `)' (used for disambiguating dangling else)
-    \end{enumerate}
-\end{enumerate}
-%
-The keywords are: `as', `bool', `break', `by', `continue', `else', `f32', `f64', `false', `fn', `for', `i8', `i16', `i32', `i64', `if', `inout', `let', `match', `module', `pub', `return', `size', `struct', `then', `to', `true', `type', `u8', `u16', `u32', `u64', `union', `use', `void', and `while'.
-
-\section{Type System}\label{sec:types}
-TODO
-
-\section{Semantics}\label{sec:semantics}
-TODO
-
-\end{document}