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---
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
| ‘`’ stringLiteral ‘`’
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 ::= ‘'’ (printableChar | charEscapeSeq) ‘'’
stringLiteral ::= ‘"’ {stringElement} ‘"’
| ‘"""’ multiLineChars ‘"""’
stringElement ::= (printableChar except ‘"’)
| 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}
-->
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