Modelica® Language Specification version 3.6-dev

Appendix A Modelica Concrete Syntax

(January 25, 2021)

A.1 Lexical conventions

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

⬇
[ ] optional
{ } repeat zero or more times
| or
"text" The text is treated as a single token (no white-space between any characters)

The following lexical units are defined (the ones in boldface are the ones used in the grammar, the rest are just internal to the definition of other lexical units):

⬇
IDENT = NONDIGIT { DIGIT | NONDIGIT } | Q-IDENT
Q-IDENT = "’" { Q-CHAR | S-ESCAPE } "’"
NONDIGIT = "_" | letters "a" to "z" | letters "A" to "Z"
STRING = """ { S-CHAR | S-ESCAPE } """
S-CHAR = see below
Q-CHAR = NONDIGIT | DIGIT | "!" | "#" | "$" | "%" | "&" | "(" | ")"
   | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | ">" | "="
   | "?" | "@" | "[" | "]" | "^" | "{" | "}" | "|" | "~" | " " | """
S-ESCAPE = "\’" | "\"" | "\?" | "\\"
   | "\a" | "\b" | "\f" | "\n" | "\r" | "\t" | "\v"
DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
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. E.g. ’x’ and x are different IDENTs.

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