chapters/syntax.tex

\chapter{Modelica Concrete Syntax}\label{modelica-concrete-syntax}

\section{Lexical conventions}\label{lexical-conventions}

The following syntactic metasymbols are used (extended BNF):
\begin{center}
\begin{tabular}{c l}
\hline
\tablehead{Syntax} & \tablehead{Description}\\
\hline
\hline
{\lstinline[language=grammar]![ $\ldots$ ]!} & Optional\\
{\lstinline[language=grammar]!{ $\ldots$ }!} & Repeat zero or more times\\
{\lstinline[language=grammar]!$\ldots$ | $\ldots$!} & Alternatives\\
{\lstinline[language=grammar]!"$\mathit{text}$"!} & The $\mathit{text}$ is treated as a single token (no white-space between any characters)\\
\hline
\end{tabular}
\end{center}

The following lexical units are defined:
% Beware that the first lines of the lexing rules below are duplicated in \cref{identifiers}, and must be kept in sync.
\begin{lstlisting}[language=grammar]
IDENT = NON-DIGIT { DIGIT | NON-DIGIT } | Q-IDENT
Q-IDENT = "'" { Q-CHAR | S-ESCAPE } "'"
NON-DIGIT = "_" | letters "a" $\ldots$ "z" | letters "A" $\ldots$ "Z"
DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
Q-CHAR = NON-DIGIT | DIGIT | "!" | "#" | "$\mbox{\textdollar}$" | "%" | "&" | "(" | ")"
   | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | ">" | "="
   | "?" | "@" | "[" | "]" | "^" | "{" | "}" | "|" | "~" | " " | """
S-ESCAPE = "\'" | "\"" | "\?" | "\\"
   | "\a" | "\b" | "\f" | "\n" | "\r" | "\t" | "\v"
STRING = """ { S-CHAR | S-ESCAPE } """
S-CHAR = see below
UNSIGNED-INTEGER = DIGIT { DIGIT }
UNSIGNED-REAL =
   UNSIGNED-INTEGER  "." [ UNSIGNED-INTEGER ]
   | UNSIGNED_INTEGER [ "." [ UNSIGNED_INTEGER ] ]
     ( "e" | "E" ) [ "+" | "-" ] UNSIGNED-INTEGER
   | "."  UNSIGNED-INTEGER [ ( "e" | "E" ) [ "+" | "-" ] UNSIGNED-INTEGER ]
\end{lstlisting}
\lstinline[language=grammar]!S-CHAR! is any member of the Unicode character set (\url{https://unicode.org}; see \cref{mapping-package-class-structures-to-a-hierarchical-file-system} for storing as UTF-8 on files) except double-quote `"', and backslash `\textbackslash{}'.

For identifiers the redundant escapes (`\lstinline!\?!' and `\lstinline!\"!') are the same as the corresponding non-escaped variants (`\lstinline!?!' and '\lstinline!"!').
The single quotes are part of an identifier.
For example, the identifiers \lstinline!'x'! and \lstinline!x! are different.

Note:
\begin{itemize}
\item
  White-space and comments can be used between separate lexical units and/or symbols, and also separates them. Each lexical unit will consume the maximum number of characters from the input stream.
  White-space and comments cannot be used inside other lexical units, except for \lstinline[language=grammar]!STRING! and \lstinline[language=grammar]!Q-IDENT! where they are treated as part of the \lstinline[language=grammar]!STRING! or \lstinline[language=grammar]!Q-IDENT! lexical unit.
\item
  Concatenation of string literals requires a binary expression.
  For example, \lstinline!"a" + "b"! evaluates to \lstinline!"ab"!.
  There is no support for the C/C++ style of concatenating adjacent string literal tokens (for example, \lstinline[language=C]!"a" "b"! becoming \lstinline[language=C]!"ab"!).
\item
  Modelica uses the same comment syntax as C++ and Java (i.e., \lstinline!//! signals the start of a line comment and \lstinline!/* $\ldots$ */! is a multi-line comment); comments may contain any Unicode character.
  Modelica also has structured comments in the form of annotations and string comments.
\item
  In the grammar, keywords of the Modelica language are highlighted with color, for example, \lstinline[language=grammar]!equation!.
\item
  Productions use hyphen as separator both in the grammar and in the text.
  (Previously the grammar used underscore.)
\end{itemize}
\begin{nonnormative}
  Within a description-string the optional tags \lstinline!<HTML>! and \lstinline!</HTML>! or \lstinline!<html>! and \lstinline!</html>! define the start and end of content that is HTML encoded.
  \end{nonnormative}
\section{Grammar}\label{grammar}

\subsection{Stored Definition -- Within}\label{stored-definition-within}

\begin{lstlisting}[language=grammar]
stored-definition :
   [ within [ name ] ";" ]
   { [ final ] class-definition ";" }
\end{lstlisting}

\subsection{Class Definition}\label{class-definition}

\begin{lstlisting}[language=grammar]
class-definition :
   [ encapsulated ] class-prefixes class-specifier

class-prefixes :
   [ partial ]
   ( class
     | model
     | [ operator ] record
     | block
     | [ expandable ] connector
     | type
     | package
     | [ pure | impure ] [ operator ] function
     | operator
   )

class-specifier :
   long-class-specifier | short-class-specifier | der-class-specifier

long-class-specifier :
   IDENT description-string composition end IDENT
   | extends IDENT [ class-modification ] description-string composition
     end IDENT

short-class-specifier :
   IDENT "=" base-prefix type-specifier [ array-subscripts ]
   [ class-modification ] description
   | IDENT "=" enumeration "(" ( [ enum-list ] | ":" ) ")" description

der-class-specifier :
   IDENT "=" der "(" type-specifier "," IDENT { "," IDENT } ")" description

base-prefix :
   [ input | output ]

enum-list :
   enumeration-literal { "," enumeration-literal }

enumeration-literal :
   IDENT description

composition :
   element-list
   { public element-list
     | protected element-list
     | equation-section
     | algorithm-section
   }
   [ external [ language-specification ]
     [ external-function-call ] [ annotation-clause ] ";"
   ]
   [ annotation-clause ";" ]

language-specification :
   STRING

external-function-call :
   [ component-reference "=" ]
   IDENT "(" [ expression-list ] ")"

element-list :
   { element ";" }

element :
   import-clause
   | extends-clause
   | [ redeclare ]
     [ final ]
     [ inner ] [ outer ]
     ( class-definition
       | component-clause
       | replaceable ( class-definition | component-clause )
         [ constraining-clause description ]
     )

import-clause :
   import
   ( IDENT "=" name
     | name [ ".*" | "." ( "*" | "{" import-list "}" ) ]
   )
   description

import-list :
   IDENT { "," IDENT }
\end{lstlisting}

\subsection{Extends}\label{extends}

\begin{lstlisting}[language=grammar]
extends-clause :
   extends type-specifier [ class-or-inheritance-modification ] [ annotation-clause ]

constraining-clause :
   constrainedby type-specifier [ class-modification ]

class-or-inheritance-modification :
   "(" [ argument-or-inheritance-modification-list ] ")"

argument-or-inheritance-modification-list :
    ( argument | inheritance-modification ) { "," ( argument | inheritance-modification ) }

inheritance-modification :
    break ( connect-clause | IDENT )
\end{lstlisting}

\subsection{Component Clause}\label{component-clause}

\begin{lstlisting}[language=grammar]
component-clause :
   type-prefix type-specifier [ array-subscripts ] component-list

type-prefix :
   [ flow | stream ]
   [ discrete | parameter | constant ]
   [ input | output ]

component-list :
   component-declaration { "," component-declaration }

component-declaration :
   declaration [ condition-attribute ] description

condition-attribute :
   if expression

declaration :
   IDENT [ array-subscripts ] [ modification ]
\end{lstlisting}

\subsection{Modification}\label{modification}

\begin{lstlisting}[language=grammar]
modification :
   class-modification [ "=" modification-expression ]
   | "=" modification-expression
   | ":=" modification-expression

modification-expression :
   expression
   | break

class-modification :
   "(" [ argument-list ] ")"

argument-list :
   argument { "," argument }

argument :
   element-modification-or-replaceable
   | element-redeclaration

element-modification-or-replaceable :
   [ each ] [ final ] ( element-modification | element-replaceable )

element-modification :
   name [ modification ] description-string

element-redeclaration :
   redeclare [ each ] [ final ]
   ( short-class-definition | component-clause1 | element-replaceable )

element-replaceable :
   replaceable ( short-class-definition | component-clause1 )
   [ constraining-clause ]

component-clause1 :
   type-prefix type-specifier component-declaration1

component-declaration1 :
   declaration description

short-class-definition :
   class-prefixes short-class-specifier
\end{lstlisting}


\subsection{Equations}\label{equations1}

\begin{lstlisting}[language=grammar]
equation-section :
   [ initial ] equation { equation ";" }

algorithm-section :
   [ initial ] algorithm { statement ";" }

equation :
   ( simple-expression "=" expression
     | if-equation
     | for-equation
     | connect-equation
     | when-equation
     | component-reference function-call-args
   )
   description

statement :
   ( component-reference ( ":=" expression | function-call-args )
     | "(" output-expression-list ")" ":="
       component-reference function-call-args
     | break
     | return
     | if-statement
     | for-statement
     | while-statement
     | when-statement
   )
   description

if-equation :
   if expression then
     { equation ";" }
   { elseif expression then
     { equation ";" }
   }
   [ else
     { equation ";" }
   ]
   end if

if-statement :
   if expression then
     { statement ";" }
   { elseif expression then
     { statement ";" }
   }
   [ else
     { statement ";" }
   ]
   end if

for-equation :
   for for-indices loop
     { equation ";" }
   end for

for-statement :
   for for-indices loop
     { statement ";" }
   end for

for-indices :
   for-index { "," for-index }

for-index :
   IDENT [ in expression ]

while-statement :
   while expression loop
     { statement ";" }
   end while

when-equation :
   when expression then
     { equation ";" }
   { elsewhen expression then
     { equation ";" }
   }
   end when

when-statement :
   when expression then
     { statement ";" }
   { elsewhen expression then
     { statement ";" }
   }
   end when

connect-equation :
   connect "(" component-reference "," component-reference ")"
\end{lstlisting}

\subsection{Expressions}\label{expressions1}

\begin{lstlisting}[language=grammar]
expression :
   simple-expression
   | if expression then expression
     { elseif expression then expression }
     else expression

simple-expression :
   logical-expression [ ":" logical-expression [ ":" logical-expression ] ]

logical-expression :
   logical-term { or logical-term }

logical-term :
   logical-factor { and logical-factor }

logical-factor :
   [ not ] relation

relation :
   arithmetic-expression [ relational-operator arithmetic-expression ]

relational-operator :
   "<" | "<=" | ">" | ">=" | "==" | "<>"

arithmetic-expression :
   [ add-operator ] term { add-operator term }

add-operator :
   "+" | "-" | ".+" | ".-"

term :
   factor { mul-operator factor }

mul-operator :
   "*" | "/" | ".*" | "./"

factor :
   primary [ ("^" | ".^") primary ]

primary :
   UNSIGNED-NUMBER
   | STRING
   | false
   | true
   | ( component-reference | der | initial | pure ) function-call-args
   | component-reference
   | "(" output-expression-list ")"
   | "[" expression-list { ";" expression-list } "]"
   | "{" array-arguments "}"
   | end

UNSIGNED-NUMBER :
   UNSIGNED-INTEGER | UNSIGNED-REAL

type-specifier :
   ["."] name

name :
   IDENT { "." IDENT }

component-reference :
   [ "." ] IDENT [ array-subscripts ] { "." IDENT [ array-subscripts ] }

result-reference :
   component-reference
   | der "(" component-reference [ "," UNSIGNED-INTEGER ] ")"

function-call-args :
   "(" [ function-arguments ] ")"

function-arguments :
   expression [ "," function-arguments-non-first | for for-indices ]
   | function-partial-application [ "," function-arguments-non-first ]
   | named-arguments

function-arguments-non-first :
   function-argument [ "," function-arguments-non-first ]
   | named-arguments

array-arguments :
   expression [ "," array-arguments-non-first | for for-indices ]

array-arguments-non-first :
   expression [ "," array-arguments-non-first ]

named-arguments: named-argument [ "," named-arguments ]

named-argument: IDENT "=" function-argument

function-argument :
   function-partial-application | expression

function-partial-application :
   function type-specifier "(" [ named-arguments ] ")"

output-expression-list :
   [ expression ] { "," [ expression ] }

expression-list :
   expression { "," expression }

array-subscripts :
   "[" subscript { "," subscript } "]"

subscript :
   ":" | expression

description :
   description-string [ annotation-clause ]

description-string :
   [ STRING { "+" STRING } ]

annotation-clause :
   annotation class-modification
\end{lstlisting}