EBNF Definition of the Oberon programming language

Extracted from the book Programmieren in Oberon - Das neue Pascal by N. Wirth and M. Reiser and translated by J. Templ.

module  =  MODULE ident ";"  [ImportList] DeclarationSequence 

    [BEGIN StatementSequence] END ident ".". 

ident  =  letter {letter | digit}. 

letter =  "A" .. "Z" | "a" .. "z". 

digit  =  "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9". 

ImportList  =  IMPORT import {"," import} ";". 

import  =  ident [":=" ident]. 

DeclarationSequence  =  {CONST {ConstantDeclaration ";"} | 

    TYPE {TypeDeclaration ";"} | VAR {VariableDeclaration ";"}} 

    {ProcedureDeclaration ";" | ForwardDeclaration ";"}. 

ConstantDeclaration  =  identdef "=" ConstExpression. 

identdef  =  ident ["*"]. 

ConstExpression  =  expression. 

expression  =  SimpleExpression [relation SimpleExpression]. 

SimpleExpression  =  ["+"|"-"] term {AddOperator term}. 

term  =  factor {MulOperator factor}. 

factor  =  number | CharConstant | string | NIL | set | 

    designator [ActualParameters] | "(" expression ")" | "~" factor. 

number  =  integer | real. 

integer  =  digit {digit} | digit {hexDigit} "H". 

hexDigit  =  digit | "A" | "B" | "C" | "D" | "E" | "F". 

real  =  digit {digit} "." {digit} [ScaleFactor]. 

ScaleFactor  =  ("E" | "D") ["+" | "-"] digit {digit}. 

CharConstant  =  '"' character '"' | digit {hexDigit} "X". 

string  =  '"' {character} '"'. 

set  =  "{" [element {"," element}] "}". 

element  =  expression [".." expression]. 

designator  =  qualident {"." ident | "[" ExpList "]" | "(" qualident ")" | "^" }. 

ExpList  =  expression {"," expression}. 

ActualParameters  =  "(" [ExpList] ")". 

MulOperator  =  "*" | "/" | DIV | MOD | "&". 

AddOperator  =  "+" | "-" | OR. 

relation  =  "=" | "#" | "<" | "<=" | ">" | ">=" | IN | IS. 

TypeDeclaration  =  identdef "=" type. 

type  =  qualident | ArrayType | RecordType | PointerType | ProcedureType. 

qualident  =  [ident "."] ident. 

ArrayType  =  ARRAY length {"," length} OF type. 

length  =  ConstExpression. 

RecordType  =  RECORD ["(" BaseType ")"] FieldListSequence END. 

BaseType  =  qualident. 

FieldListSequence  =  FieldList {";" FieldList}. 

FieldList  =  [IdentList ":" type]. 

IdentList  =  identdef {"," identdef}. 

PointerType  =  POINTER TO type. 

ProcedureType  =  PROCEDURE [FormalParameters]. 

VariableDeclaration  =  IdentList ":" type. 

ProcedureDeclaration  =  ProcedureHeading ";" ProcedureBody ident. 

ProcedureHeading  =  PROCEDURE ["*"] identdef [FormalParameters]. 

FormalParameters  =  "(" [FPSection {";" FPSection}] ")" [":" qualident]. 

FPSection  =  [VAR] ident {"," ident} ":" FormalType. 

FormalType  =  {ARRAY OF} (qualident | ProcedureType). 

ProcedureBody  =  DeclarationSequence [BEGIN StatementSequence] END. 

ForwardDeclaration  =  PROCEDURE "^" ident ["*"] [FormalParameters]. 

StatementSequence  =  statement {";" statement}. 

statement  =  [assignment | ProcedureCall | 

    IfStatement | CaseStatement | WhileStatement | RepeatStatement | 

    LoopStatement | WithStatement | EXIT | RETURN [expression] ]. 

assignment  =  designator ":=" expression. 

ProcedureCall  =  designator [ActualParameters]. 

IfStatement  =  IF expression THEN StatementSequence 

    {ELSIF expression THEN StatementSequence} 

    [ELSE StatementSequence] END. 

CaseStatement  =  CASE expression OF case {"|" case} 

    [ELSE StatementSequence] END. 

case  =  [CaseLabelList ":" StatementSequence]. 

CaseLabelList  =  CaseLabels {"," CaseLabels}. 

CaseLabels  =  ConstExpression [".." ConstExpression]. 

WhileStatement  =  WHILE expression DO StatementSequence END. 

RepeatStatement  =  REPEAT StatementSequence UNTIL expression. 

LoopStatement  =  LOOP StatementSequence END. 

WithStatement  =  WITH qualident ":" qualident DO StatementSequence END.

EBNF definition of a Module Definition ( .Def)

A module definition follows the Oberon grammar. The only differences are in the productions:

module  =  DEFINITION ident ";"  [ImportList] DeclarationSequence END ident ".".

where the body is removed and in:

ProcedureDeclaration  = ProcedureHeading ";"

where ProcedureBody and ident are removed. All the productions from ProcedureBody may be ignored. Depending on the tool (Watson or Browser), the export marks may or may not be included in the output.