Modelica® Language Specification version 3.6-dev

Appendix A Modelica Concrete Syntax

(May 11, 2023)

A.1 Lexical conventions

The following syntactic meta symbols are used (extended BNF):

Syntax Description
[ … ] Optional
{ … } Repeat zero or more times
… | … Alternatives
"𝑡𝑒𝑥𝑡" The 𝑡𝑒𝑥𝑡 is treated as a single token (no white-space between any characters)

The following lexical units are defined:

⬇
IDENT = NON-DIGIT { DIGIT | NON-DIGIT } | Q-IDENT
Q-IDENT = "’" { Q-CHAR | S-ESCAPE } "’"
NON-DIGIT = "_" | letters "a" … "z" | letters "A" … "Z"
DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
Q-CHAR = NON-DIGIT | DIGIT | "!" | "#" | "$" | "%" | "&" | "(" | ")"
   | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | ">" | "="
   | "?" | "@" | "[" | "]" | "^" | "{" | "}" | "|" | "~" | " " | """
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 ]

S-CHAR is any member of the Unicode character set (http://www.unicode.org; see section 13.4 for storing as UTF-8 on files) except double-quote ‘"’, and backslash ‘\’.

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

Note:

  • •

    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 STRING and Q-IDENT where they are treated as part of the STRING or Q-IDENT lexical unit.

  • •

    Concatenation of string literals requires a binary expression. For example, "a" + "b" evaluates to "ab". There is no support for the C/C++ style of concatenating adjacent string literal tokens (for example, "a" "b" becoming "ab").

  • •

    Modelica uses the same comment syntax as C++ and Java (i.e., // signals the start of a line comment and /* … */ is a multi-line comment); comments may contain any Unicode character. Modelica also has structured comments in the form of annotations and string comments.

  • •

    Each description-string or string in annotations (= STRING with production annotation-clause in the grammar) may contain any member of the Unicode character set. All other strings have to contain only the sub-set of Unicode characters identical with the 7-bit US-ASCII character set.

    [As a consequence, operators like ‘>’ or ‘<’, and external functions only operate on ASCII strings and not on Unicode-strings. Within a description-string the tags <HTML> and </HTML> or <html> and </html> define optionally begin and end of content that is HTML encoded.]

  • •

    Boldface denotes keywords of the Modelica language. Keywords are reserved words and shall not be used as identifiers.

  • •

    Productions use hyphen as separator both in the grammar and in the text. Previously the grammar used underscore.

A.2 Grammar

A.2.1 Stored Definition – Within

⬇
stored-definition :
   [ within [ name ] ";" ]
   { [ final ] class-definition ";" }

A.2.2 Class Definition

⬇
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 }

A.2.3 Extends

⬇
extends-clause :
   extends type-specifier [ class-modification ] [ annotation-clause ]
constraining-clause :
   constrainedby type-specifier [ class-modification ]

A.2.4 Component Clause

⬇
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 ]

A.2.5 Modification

⬇
modification :
   class-modification [ "=" expression ]
   | "=" expression
   | ":=" expression
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

A.2.6 Equations

⬇
equation-section :
   [ initial ] equation { equation ";" }
algorithm-section :
   [ initial ] algorithm { statement ";" }
equation :
   ( simple-expression "=" expression
     | if-equation
     | for-equation
     | connect-clause
     | 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-clause :
   connect "(" component-reference "," component-reference ")"

A.2.7 Expressions

⬇
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 ] }
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