path: root/spec/13-syntax-summary.md

---
title: Syntax Summary
layout: default
chapter: 13
---

# Syntax Summary

The following descriptions of Scala tokens uses literal characters `‘c’` when referring to the ASCII fragment `\u0000` – `\u007F`.

_Unicode escapes_ are used to represent the Unicode character with the given hexadecimal code:

```ebnf
UnicodeEscape ::= ‘\’ ‘u’ {‘u’} hexDigit hexDigit hexDigit hexDigit
hexDigit      ::= ‘0’ | … | ‘9’ | ‘A’ | … | ‘F’ | ‘a’ | … | ‘f’
```

## Lexical Syntax

The lexical syntax of Scala is given by the following grammar in EBNF form:

```ebnf
whiteSpace       ::=  ‘\u0020’ | ‘\u0009’ | ‘\u000D’ | ‘\u000A’
upper            ::=  ‘A’ | … | ‘Z’ | ‘\$’ | ‘_’  // and Unicode category Lu
lower            ::=  ‘a’ | … | ‘z’ // and Unicode category Ll
letter           ::=  upper | lower // and Unicode categories Lo, Lt, Nl
digit            ::=  ‘0’ | … | ‘9’
paren            ::=  ‘(’ | ‘)’ | ‘[’ | ‘]’ | ‘{’ | ‘}’
delim            ::=  ‘`’ | ‘'’ | ‘"’ | ‘.’ | ‘;’ | ‘,’
opchar           ::= // printableChar not matched by (whiteSpace | upper | lower |
                     // letter | digit | paren | delim | opchar | Unicode_Sm | Unicode_So)
printableChar    ::= // all characters in [\u0020, \u007F] inclusive
charEscapeSeq    ::= ‘\’ (‘b’ | ‘t’ | ‘n’ | ‘f’ | ‘r’ | ‘"’ | ‘'’ | ‘\’)

op               ::=  opchar {opchar}
varid            ::=  lower idrest
plainid          ::=  upper idrest
                 |  varid
                 |  op
id               ::=  plainid
                 |  ‘`’ { charNoBackQuoteOrNewline | UnicodeEscape | charEscapeSeq } ‘`’
idrest           ::=  {letter | digit} [‘_’ op]

integerLiteral   ::=  (decimalNumeral | hexNumeral) [‘L’ | ‘l’]
decimalNumeral   ::=  ‘0’ | nonZeroDigit {digit}
hexNumeral       ::=  ‘0’ (‘x’ | ‘X’) hexDigit {hexDigit}
digit            ::=  ‘0’ | nonZeroDigit
nonZeroDigit     ::=  ‘1’ | … | ‘9’

floatingPointLiteral
                 ::=  digit {digit} ‘.’ digit {digit} [exponentPart] [floatType]
                 |  ‘.’ digit {digit} [exponentPart] [floatType]
                 |  digit {digit} exponentPart [floatType]
                 |  digit {digit} [exponentPart] floatType
exponentPart     ::=  (‘E’ | ‘e’) [‘+’ | ‘-’] digit {digit}
floatType        ::=  ‘F’ | ‘f’ | ‘D’ | ‘d’

booleanLiteral   ::=  ‘true’ | ‘false’

characterLiteral ::=  ‘'’ (charNoQuoteOrNewline | UnicodeEscape | charEscapeSeq) ‘'’

stringLiteral    ::=  ‘"’ {stringElement} ‘"’
                 |  ‘"""’ multiLineChars ‘"""’
stringElement    ::=  charNoDoubleQuoteOrNewline
                 |  UnicodeEscape
                 |  charEscapeSeq
multiLineChars   ::=  {[‘"’] [‘"’] charNoDoubleQuote} {‘"’}

symbolLiteral    ::=  ‘'’ plainid

comment          ::=  ‘/*’ “any sequence of characters; nested comments are allowed” ‘*/’
                 |  ‘//’ “any sequence of characters up to end of line”

nl               ::=  $\mathit{“new line character”}$
semi             ::=  ‘;’ |  nl {nl}
```

## Context-free Syntax

The context-free syntax of Scala is given by the following EBNF
grammar:

```ebnf
  Literal           ::=  [‘-’] integerLiteral
                      |  [‘-’] floatingPointLiteral
                      |  booleanLiteral
                      |  characterLiteral
                      |  stringLiteral
                      |  symbolLiteral
                      |  ‘null’

  QualId            ::=  id {‘.’ id}
  ids               ::=  id {‘,’ id}

  Path              ::=  StableId
                      |  [id ‘.’] ‘this’
  StableId          ::=  id
                      |  Path ‘.’ id
                      |  [id ‘.’] ‘super’ [ClassQualifier] ‘.’ id
  ClassQualifier    ::=  ‘[’ id ‘]’

  Type              ::=  FunctionArgTypes ‘=>’ Type
                      |  InfixType [ExistentialClause]
  FunctionArgTypes  ::= InfixType
                      | ‘(’ [ ParamType {‘,’ ParamType } ] ‘)’
  ExistentialClause ::=  ‘forSome’ ‘{’ ExistentialDcl {semi ExistentialDcl} ‘}’
  ExistentialDcl    ::=  ‘type’ TypeDcl
                      |  ‘val’ ValDcl
  InfixType         ::=  CompoundType {id [nl] CompoundType}
  CompoundType      ::=  AnnotType {‘with’ AnnotType} [Refinement]
                      |  Refinement
  AnnotType         ::=  SimpleType {Annotation}
  SimpleType        ::=  SimpleType TypeArgs
                      |  SimpleType ‘#’ id
                      |  StableId
                      |  Path ‘.’ ‘type’
                      |  ‘(’ Types ‘)’
  TypeArgs          ::=  ‘[’ Types ‘]’
  Types             ::=  Type {‘,’ Type}
  Refinement        ::=  [nl] ‘{’ RefineStat {semi RefineStat} ‘}’
  RefineStat        ::=  Dcl
                      |  ‘type’ TypeDef
                      |
  TypePat           ::=  Type

  Ascription        ::=  ‘:’ InfixType
                      |  ‘:’ Annotation {Annotation}
                      |  ‘:’ ‘_’ ‘*’

  Expr              ::=  (Bindings | [‘implicit’] id | ‘_’) ‘=>’ Expr
                      |  Expr1
  Expr1             ::=  ‘if’ ‘(’ Expr ‘)’ {nl} Expr [[semi] ‘else’ Expr]
                      |  ‘while’ ‘(’ Expr ‘)’ {nl} Expr
                      |  ‘try’ (‘{’ Block ‘}’ | Expr) [‘catch’ ‘{’ CaseClauses ‘}’] [‘finally’ Expr]
                      |  ‘do’ Expr [semi] ‘while’ ‘(’ Expr ‘)’
                      |  ‘for’ (‘(’ Enumerators ‘)’ | ‘{’ Enumerators ‘}’) {nl} [‘yield’] Expr
                      |  ‘throw’ Expr
                      |  ‘return’ [Expr]
                      |  [SimpleExpr ‘.’] id ‘=’ Expr
                      |  SimpleExpr1 ArgumentExprs ‘=’ Expr
                      |  PostfixExpr
                      |  PostfixExpr Ascription
                      |  PostfixExpr ‘match’ ‘{’ CaseClauses ‘}’
  PostfixExpr       ::=  InfixExpr [id [nl]]
  InfixExpr         ::=  PrefixExpr
                      |  InfixExpr id [nl] InfixExpr
  PrefixExpr        ::=  [‘-’ | ‘+’ | ‘~’ | ‘!’] SimpleExpr
  SimpleExpr        ::=  ‘new’ (ClassTemplate | TemplateBody)
                      |  BlockExpr
                      |  SimpleExpr1 [‘_’]
  SimpleExpr1       ::=  Literal
                      |  Path
                      |  ‘_’
                      |  ‘(’ [Exprs] ‘)’
                      |  SimpleExpr ‘.’ id
                      |  SimpleExpr TypeArgs
                      |  SimpleExpr1 ArgumentExprs
                      |  XmlExpr
  Exprs             ::=  Expr {‘,’ Expr}
  ArgumentExprs     ::=  ‘(’ [Exprs] ‘)’
                      |  ‘(’ [Exprs ‘,’] PostfixExpr ‘:’ ‘_’ ‘*’ ‘)’
                      |  [nl] BlockExpr
  BlockExpr         ::=  ‘{’ CaseClauses ‘}’
                      |  ‘{’ Block ‘}’
  Block             ::=  BlockStat {semi BlockStat} [ResultExpr]
  BlockStat         ::=  Import
                      |  {Annotation} [‘implicit’ | ‘lazy’] Def
                      |  {Annotation} {LocalModifier} TmplDef
                      |  Expr1
                      |
  ResultExpr        ::=  Expr1
                      |  (Bindings | ([‘implicit’] id | ‘_’) ‘:’ CompoundType) ‘=>’ Block

  Enumerators       ::=  Generator {semi Generator}
  Generator         ::=  Pattern1 ‘<-’ Expr {[semi] Guard | semi Pattern1 ‘=’ Expr}

  CaseClauses       ::=  CaseClause { CaseClause }
  CaseClause        ::=  ‘case’ Pattern [Guard] ‘=>’ Block
  Guard             ::=  ‘if’ PostfixExpr

  Pattern           ::=  Pattern1 { ‘|’ Pattern1 }
  Pattern1          ::=  varid ‘:’ TypePat
                      |  ‘_’ ‘:’ TypePat
                      |  Pattern2
  Pattern2          ::=  varid [‘@’ Pattern3]
                      |  Pattern3
  Pattern3          ::=  SimplePattern
                      |  SimplePattern { id [nl] SimplePattern }
  SimplePattern     ::=  ‘_’
                      |  varid
                      |  Literal
                      |  StableId
                      |  StableId ‘(’ [Patterns] ‘)’
                      |  StableId ‘(’ [Patterns ‘,’] [varid ‘@’] ‘_’ ‘*’ ‘)’
                      |  ‘(’ [Patterns] ‘)’
                      |  XmlPattern
  Patterns          ::=  Pattern [‘,’ Patterns]
                      |  ‘_’ ‘*’

  TypeParamClause   ::=  ‘[’ VariantTypeParam {‘,’ VariantTypeParam} ‘]’
  FunTypeParamClause::=  ‘[’ TypeParam {‘,’ TypeParam} ‘]’
  VariantTypeParam  ::=  {Annotation} [‘+’ | ‘-’] TypeParam
  TypeParam         ::=  (id | ‘_’) [TypeParamClause] [‘>:’ Type] [‘<:’ Type]
                         {‘<%’ Type} {‘:’ Type}
  ParamClauses      ::=  {ParamClause} [[nl] ‘(’ ‘implicit’ Params ‘)’]
  ParamClause       ::=  [nl] ‘(’ [Params] ‘)’
  Params            ::=  Param {‘,’ Param}
  Param             ::=  {Annotation} id [‘:’ ParamType] [‘=’ Expr]
  ParamType         ::=  Type
                      |  ‘=>’ Type
                      |  Type ‘*’
  ClassParamClauses ::=  {ClassParamClause}
                         [[nl] ‘(’ ‘implicit’ ClassParams ‘)’]
  ClassParamClause  ::=  [nl] ‘(’ [ClassParams] ‘)’
  ClassParams       ::=  ClassParam {‘,’ ClassParam}
  ClassParam        ::=  {Annotation} {Modifier} [(‘val’ | ‘var’)]
                         id ‘:’ ParamType [‘=’ Expr]
  Bindings          ::=  ‘(’ Binding {‘,’ Binding} ‘)’
  Binding           ::=  (id | ‘_’) [‘:’ Type]

  Modifier          ::=  LocalModifier
                      |  AccessModifier
                      |  ‘override’
  LocalModifier     ::=  ‘abstract’
                      |  ‘final’
                      |  ‘sealed’
                      |  ‘implicit’
                      |  ‘lazy’
  AccessModifier    ::=  (‘private’ | ‘protected’) [AccessQualifier]
  AccessQualifier   ::=  ‘[’ (id | ‘this’) ‘]’

  Annotation        ::=  ‘@’ SimpleType {ArgumentExprs}
  ConstrAnnotation  ::=  ‘@’ SimpleType ArgumentExprs

  TemplateBody      ::=  [nl] ‘{’ [SelfType] TemplateStat {semi TemplateStat} ‘}’
  TemplateStat      ::=  Import
                      |  {Annotation [nl]} {Modifier} Def
                      |  {Annotation [nl]} {Modifier} Dcl
                      |  Expr
                      |
  SelfType          ::=  id [‘:’ Type] ‘=>’
                      |  ‘this’ ‘:’ Type ‘=>’

  Import            ::=  ‘import’ ImportExpr {‘,’ ImportExpr}
  ImportExpr        ::=  StableId ‘.’ (id | ‘_’ | ImportSelectors)
  ImportSelectors   ::=  ‘{’ {ImportSelector ‘,’} (ImportSelector | ‘_’) ‘}’
  ImportSelector    ::=  id [‘=>’ id | ‘=>’ ‘_’]

  Dcl               ::=  ‘val’ ValDcl
                      |  ‘var’ VarDcl
                      |  ‘def’ FunDcl
                      |  ‘type’ {nl} TypeDcl

  ValDcl            ::=  ids ‘:’ Type
  VarDcl            ::=  ids ‘:’ Type
  FunDcl            ::=  FunSig [‘:’ Type]
  FunSig            ::=  id [FunTypeParamClause] ParamClauses
  TypeDcl           ::=  id [TypeParamClause] [‘>:’ Type] [‘<:’ Type]

  PatVarDef         ::=  ‘val’ PatDef
                      |  ‘var’ VarDef
  Def               ::=  PatVarDef
                      |  ‘def’ FunDef
                      |  ‘type’ {nl} TypeDef
                      |  TmplDef
  PatDef            ::=  Pattern2 {‘,’ Pattern2} [‘:’ Type] ‘=’ Expr
  VarDef            ::=  PatDef
                      |  ids ‘:’ Type ‘=’ ‘_’
  FunDef            ::=  FunSig [‘:’ Type] ‘=’ Expr
                      |  FunSig [nl] ‘{’ Block ‘}’
                      |  ‘this’ ParamClause ParamClauses
                         (‘=’ ConstrExpr | [nl] ConstrBlock)
  TypeDef           ::=  id [TypeParamClause] ‘=’ Type

  TmplDef           ::=  [‘case’] ‘class’ ClassDef
                      |  [‘case’] ‘object’ ObjectDef
                      |  ‘trait’ TraitDef
  ClassDef          ::=  id [TypeParamClause] {ConstrAnnotation} [AccessModifier]
                         ClassParamClauses ClassTemplateOpt
  TraitDef          ::=  id [TypeParamClause] TraitTemplateOpt
  ObjectDef         ::=  id ClassTemplateOpt
  ClassTemplateOpt  ::=  ‘extends’ ClassTemplate | [[‘extends’] TemplateBody]
  TraitTemplateOpt  ::=  ‘extends’ TraitTemplate | [[‘extends’] TemplateBody]
  ClassTemplate     ::=  [EarlyDefs] ClassParents [TemplateBody]
  TraitTemplate     ::=  [EarlyDefs] TraitParents [TemplateBody]
  ClassParents      ::=  Constr {‘with’ AnnotType}
  TraitParents      ::=  AnnotType {‘with’ AnnotType}
  Constr            ::=  AnnotType {ArgumentExprs}
  EarlyDefs         ::= ‘{’ [EarlyDef {semi EarlyDef}] ‘}’ ‘with’
  EarlyDef          ::=  {Annotation [nl]} {Modifier} PatVarDef

  ConstrExpr        ::=  SelfInvocation
                      |  ConstrBlock
  ConstrBlock       ::=  ‘{’ SelfInvocation {semi BlockStat} ‘}’
  SelfInvocation    ::=  ‘this’ ArgumentExprs {ArgumentExprs}

  TopStatSeq        ::=  TopStat {semi TopStat}
  TopStat           ::=  {Annotation [nl]} {Modifier} TmplDef
                      |  Import
                      |  Packaging
                      |  PackageObject
                      |
  Packaging         ::=  ‘package’ QualId [nl] ‘{’ TopStatSeq ‘}’
  PackageObject     ::=  ‘package’ ‘object’ ObjectDef

  CompilationUnit   ::=  {‘package’ QualId semi} TopStatSeq
```

<!-- TODO add:
SeqPattern ::= ...

SimplePattern    ::= StableId  [TypePatArgs] [‘(’ [SeqPatterns] ‘)’]
TypePatArgs ::= ‘[’ TypePatArg {‘,’ TypePatArg} ‘]’
TypePatArg    ::=  ‘_’ |   varid}

-->