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---
layout: doc-page
title: "Scala 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’
```
Informal descriptions are typeset as `“some comment”`.
### 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
alphaid ::= upper idrest
| varid
plainid ::= alphaid
| op
id ::= plainid
| ‘`’ { charNoBackQuoteOrNewline | UnicodeEscape | charEscapeSeq } ‘`’
| INT // interpolation id, only for quasi-quotes
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} [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 \ (‘"’ | ‘\’)
| UnicodeEscape
| charEscapeSeq
multiLineChars ::= {[‘"’] [‘"’] char \ ‘"’} {‘"’}
processedStringLiteral
::= alphaid ‘"’ {printableChar \ (‘"’ | ‘$’) | escape} ‘"’
| alphaid ‘"""’ {[‘"’] [‘"’] char \ (‘"’ | ‘$’) | escape} {‘"’} ‘"""’
escape ::= ‘$$’
| ‘$’ letter { letter | digit }
| ‘{’ Block [‘;’ whiteSpace stringFormat whiteSpace] ‘}’
stringFormat ::= {printableChar \ (‘"’ | ‘}’ | ‘ ’ | ‘\t’ | ‘\n’)}
symbolLiteral ::= ‘'’ plainid
comment ::= ‘/*’ “any sequence of characters; nested comments are allowed” ‘*/’
| ‘//’ “any sequence of characters up to end of line”
nl ::= “new line character”
semi ::= ‘;’ | nl {nl}
```
## Context-free Syntax
The context-free syntax of Scala is given by the following EBNF
grammar:
### Literals and Paths
```ebnf
SimpleLiteral ::= [‘-’] integerLiteral
| [‘-’] floatingPointLiteral
| booleanLiteral
| characterLiteral
| stringLiteral
Literal ::= SimpleLiteral
| processedStringLiteral
| symbolLiteral
| ‘null’
QualId ::= id {‘.’ id}
ids ::= id {‘,’ id}
Path ::= StableId
| [id ‘.’] ‘this’
StableId ::= id
| Path ‘.’ id
| [id ‘.’] ‘super’ [ClassQualifier] ‘.’ id
ClassQualifier ::= ‘[’ id ‘]’
```
### Types
```ebnf
Type ::= [‘implicit’] FunArgTypes ‘=>’ Type Function(ts, t)
| HkTypeParamClause ‘=>’ Type TypeLambda(ps, t)
| InfixType
FunArgTypes ::= InfixType
| ‘(’ [ FunArgType {‘,’ FunArgType } ] ‘)’
InfixType ::= RefinedType {id [nl] RefinedType} InfixOp(t1, op, t2)
RefinedType ::= WithType {[nl] Refinement} RefinedTypeTree(t, ds)
WithType ::= AnnotType {‘with’ AnnotType} (deprecated)
AnnotType ::= SimpleType {Annotation} Annotated(t, annot)
SimpleType ::= SimpleType TypeArgs AppliedTypeTree(t, args)
| SimpleType ‘#’ id Select(t, name)
| StableId
| Path ‘.’ ‘type’ SingletonTypeTree(p)
| ‘(’ ArgTypes ‘)’ Tuple(ts)
| ‘_’ TypeBounds
| Refinement RefinedTypeTree(EmptyTree, refinement)
| SimpleLiteral SingletonTypeTree(l)
ArgTypes ::= Type {‘,’ Type}
| NamedTypeArg {‘,’ NamedTypeArg}
FunArgType ::= Type
| ‘=>’ Type PrefixOp(=>, t)
ParamType ::= [‘=>’] ParamValueType
ParamValueType ::= Type [‘*’] PostfixOp(t, "*")
TypeArgs ::= ‘[’ ArgTypes ‘]’ ts
NamedTypeArg ::= id ‘=’ Type NamedArg(id, t)
NamedTypeArgs ::= ‘[’ NamedTypeArg {‘,’ NamedTypeArg} ‘]’ nts
Refinement ::= ‘{’ [Dcl] {semi [Dcl]} ‘}’ ds
TypeBounds ::= [‘>:’ Type] [‘<:’ Type] | INT TypeBoundsTree(lo, hi)
TypeParamBounds ::= TypeBounds {‘<%’ Type} {‘:’ Type} ContextBounds(typeBounds, tps)
```
### Expressions
```ebnf
Expr ::= [‘implicit’] FunParams ‘=>’ Expr Function(args, expr), Function(ValDef([implicit], id, TypeTree(), EmptyTree), expr)
| Expr1
BlockResult ::= [‘implicit’] FunParams ‘=>’ Block
| Expr1
FunParams ::= Bindings
| id
| ‘_’
Expr1 ::= ‘if’ ‘(’ Expr ‘)’ {nl} Expr [[semi] ‘else’ Expr] If(Parens(cond), thenp, elsep?)
| ‘if’ Expr ‘then’ Expr [[semi] ‘else’ Expr] If(cond, thenp, elsep?)
| ‘while’ ‘(’ Expr ‘)’ {nl} Expr WhileDo(Parens(cond), body)
| ‘while’ Expr ‘do’ Expr WhileDo(cond, body)
| ‘do’ Expr [semi] ‘while’ Expr DoWhile(expr, cond)
| ‘try’ Expr Catches [‘finally’ Expr] Try(expr, catches, expr?)
| ‘try’ Expr [‘finally’ Expr] Try(expr, Nil, expr?)
| ‘throw’ Expr Throw(expr)
| ‘return’ [Expr] Return(expr?)
| ForExpr
| [SimpleExpr ‘.’] id ‘=’ Expr Assign(expr, expr)
| SimpleExpr1 ArgumentExprs ‘=’ Expr Assign(expr, expr)
| PostfixExpr [Ascription]
| PostfixExpr ‘match’ ‘{’ CaseClauses ‘}’ Match(expr, cases) -- point on match
Ascription ::= ‘:’ InfixType Typed(expr, tp)
| ‘:’ Annotation {Annotation} Typed(expr, Annotated(EmptyTree, annot)*)
Catches ::= ‘catch’ Expr
PostfixExpr ::= InfixExpr [id] PostfixOp(expr, op)
InfixExpr ::= PrefixExpr
| InfixExpr id [nl] InfixExpr InfixOp(expr, op, expr)
PrefixExpr ::= [‘-’ | ‘+’ | ‘~’ | ‘!’] SimpleExpr PrefixOp(expr, op)
SimpleExpr ::= ‘new’ Template New(templ)
| BlockExpr
| SimpleExpr1 [‘_’] PostfixOp(expr, _)
SimpleExpr1 ::= Literal
| Path
| ‘_’
| ‘(’ ExprsInParens ‘)’ Parens(exprs)
| SimpleExpr ‘.’ id Select(expr, id)
| SimpleExpr (TypeArgs | NamedTypeArgs) TypeApply(expr, args)
| SimpleExpr1 ArgumentExprs Apply(expr, args)
| XmlExpr
ExprsInParens ::= ExprInParens {‘,’ ExprInParens}
ExprInParens ::= PostfixExpr ‘:’ Type
| Expr
ParArgumentExprs ::= ‘(’ ExprsInParens ‘)’ exprs
| ‘(’ [ExprsInParens] PostfixExpr ‘:’ ‘_’ ‘*’ ‘)’ exprs :+ Typed(expr, Ident(wildcardStar))
ArgumentExprs ::= ParArgumentExprs
| [nl] BlockExpr
BlockExpr ::= ‘{’ CaseClauses ‘}’ Match(EmptyTree, cases)
| ‘{’ Block ‘}’ block // starts at {
Block ::= {BlockStat semi} [BlockResult] Block(stats, expr?)
BlockStat ::= Import
| {Annotation} [‘implicit’ | ‘lazy’] Def
| {Annotation} {LocalModifier} TmplDef
| Expr1
ForExpr ::= ‘for’ (‘(’ Enumerators ‘)’ | ‘{’ Enumerators ‘}’) ForYield(enums, expr)
{nl} [‘yield’] Expr
| ‘for’ Enumerators (‘do’ Expr | ‘yield’ Expr) ForDo(enums, expr)
Enumerators ::= Generator {semi Enumerator | Guard}
Enumerator ::= Generator
| Guard
| Pattern1 ‘=’ Expr GenAlias(pat, expr)
Generator ::= Pattern1 ‘<-’ Expr GenFrom(pat, expr)
Guard ::= ‘if’ PostfixExpr
CaseClauses ::= CaseClause { CaseClause } CaseDef(pat, guard?, block) // block starts at =>
CaseClause ::= ‘case’ (Pattern [Guard] ‘=>’ Block | INT)
Pattern ::= Pattern1 { ‘|’ Pattern1 } Alternative(pats)
Pattern1 ::= PatVar ‘:’ RefinedType Bind(name, Typed(Ident(wildcard), tpe))
| Pattern2
Pattern2 ::= [varid ‘@’] InfixPattern Bind(name, pat)
InfixPattern ::= SimplePattern { id [nl] SimplePattern } InfixOp(pat, op, pat)
SimplePattern ::= PatVar Ident(wildcard)
| Literal Bind(name, Ident(wildcard))
| ‘(’ [Patterns] ‘)’ Parens(pats) Tuple(pats)
| XmlPattern
| SimplePattern1 [TypeArgs] [ArgumentPatterns]
SimplePattern1 ::= Path
| ‘{’ Block ‘}’
| SimplePattern1 ‘.’ id
PatVar ::= varid
| ‘_’
Patterns ::= Pattern {‘,’ Pattern}
ArgumentPatterns ::= ‘(’ [Patterns] ‘)’ Apply(fn, pats)
| ‘(’ [Patterns ‘,’] Pattern2 ‘:’ ‘_’ ‘*’ ‘)’
```
### Type and Value Parameters
```ebnf
ClsTypeParamClause::= ‘[’ ClsTypeParam {‘,’ ClsTypeParam} ‘]’
ClsTypeParam ::= {Annotation} [‘+’ | ‘-’] TypeDef(Modifiers, name, tparams, bounds)
id [HkTypeParamClause] TypeParamBounds Bound(below, above, context)
DefTypeParamClause::= ‘[’ DefTypeParam {‘,’ DefTypeParam} ‘]’
DefTypeParam ::= {Annotation} id [HkTypeParamClause] TypeParamBounds
TypTypeParamClause::= ‘[’ TypTypeParam {‘,’ TypTypeParam} ‘]’
TypTypeParam ::= {Annotation} id [HkTypeParamClause] TypeBounds
HkTypeParamClause ::= ‘[’ HkTypeParam {‘,’ HkTypeParam} ‘]’
HkTypeParam ::= {Annotation} [‘+’ | ‘-’] (Id[HkTypeParamClause] | ‘_’)
TypeBounds
ClsParamClauses ::= {ClsParamClause} [[nl] ‘(’ ‘implicit’ ClsParams ‘)’]
ClsParamClause ::= [nl] ‘(’ [ClsParams] ‘)’
ClsParams ::= ClsParam {‘,’ ClsParam}
ClsParam ::= {Annotation} ValDef(mods, id, tpe, expr) -- point of mods on val/var
[{Modifier} (‘val’ | ‘var’) | ‘inline’] Param
Param ::= id ‘:’ ParamType [‘=’ Expr]
| INT
DefParamClauses ::= {DefParamClause} [[nl] ‘(’ ‘implicit’ DefParams ‘)’]
DefParamClause ::= [nl] ‘(’ [DefParams] ‘)’
DefParams ::= DefParam {‘,’ DefParam}
DefParam ::= {Annotation} [‘inline’] Param ValDef(mods, id, tpe, expr) -- point of mods at id.
```
### Bindings and Imports
```ebnf
Bindings ::= ‘(’ Binding {‘,’ Binding} ‘)’
Binding ::= (id | ‘_’) [‘:’ Type] ValDef(_, id, tpe, EmptyTree)
Modifier ::= LocalModifier
| AccessModifier
| ‘override’
LocalModifier ::= ‘abstract’
| ‘final’
| ‘sealed’
| ‘implicit’
| ‘lazy’
AccessModifier ::= (‘private’ | ‘protected’) [AccessQualifier]
AccessQualifier ::= ‘[’ (id | ‘this’) ‘]’
Annotation ::= ‘@’ SimpleType {ParArgumentExprs} Apply(tpe, args)
TemplateBody ::= [nl] ‘{’ [SelfType] TemplateStat {semi TemplateStat} ‘}’ (self, stats)
TemplateStat ::= Import
| {Annotation [nl]} {Modifier} Def
| {Annotation [nl]} {Modifier} Dcl
| EnumCaseStat
| Expr1
|
SelfType ::= id [‘:’ InfixType] ‘=>’ ValDef(_, name, tpt, _)
| ‘this’ ‘:’ InfixType ‘=>’
Import ::= ‘import’ ImportExpr {‘,’ ImportExpr}
ImportExpr ::= StableId ‘.’ (id | ‘_’ | ImportSelectors) Import(expr, sels)
ImportSelectors ::= ‘{’ {ImportSelector ‘,’} (ImportSelector | ‘_’) ‘}’
ImportSelector ::= id [‘=>’ id | ‘=>’ ‘_’] Ident(name), Pair(id, id)
```
### Declarations and Definitions
```ebnf
Dcl ::= ‘val’ ValDcl
| ‘var’ VarDcl
| ‘def’ DefDcl
| ‘type’ {nl} TypeDcl
| INT
ValDcl ::= ids ‘:’ Type PatDef(_, ids, tpe, EmptyTree)
VarDcl ::= ids ‘:’ Type PatDef(_, ids, tpe, EmptyTree)
DefDcl ::= DefSig [‘:’ Type] DefDef(_, name, tparams, vparamss, tpe, EmptyTree)
DefSig ::= id [DefTypeParamClause] DefParamClauses
TypeDcl ::= id [TypTypeParamClause] [‘=’ Type] TypeDefTree(_, name, tparams, tpt)
| id [HkTypeParamClause] TypeBounds TypeDefTree(_, name, tparams, bounds)
Def ::= ‘val’ PatDef
| ‘var’ VarDef
| ‘def’ DefDef
| ‘type’ {nl} TypeDcl
| TmplDef
| INT
PatDef ::= Pattern2 {‘,’ Pattern2} [‘:’ Type] ‘=’ Expr PatDef(_, pats, tpe?, expr)
VarDef ::= PatDef
| ids ‘:’ Type ‘=’ ‘_’
DefDef ::= DefSig [‘:’ Type] ‘=’ Expr DefDef(_, name, tparams, vparamss, tpe, expr)
| DefSig [nl] ‘{’ Block ‘}’ DefDef(_, name, tparams, vparamss, tpe, Block)
| ‘this’ DefParamClause DefParamClauses DefDef(_, <init>, Nil, vparamss, EmptyTree, expr | Block)
(‘=’ ConstrExpr | [nl] ConstrBlock)
TmplDef ::= ([‘case’ | `enum'] ‘class’ | [`enum'] trait’) ClassDef
| [‘case’ | `enum'] ‘object’ ObjectDef
| `enum' EnumDef
ClassDef ::= id ClassConstr TemplateOpt ClassDef(mods, name, tparams, templ)
ClassConstr ::= [ClsTypeParamClause] [ConstrMods] ClsParamClauses with DefDef(_, <init>, Nil, vparamss, EmptyTree, EmptyTree) as first stat
ConstrMods ::= AccessModifier
| Annotation {Annotation} (AccessModifier | ‘this’)
ObjectDef ::= id TemplateOpt ModuleDef(mods, name, template) // no constructor
EnumDef ::= id ClassConstr [`extends' [ConstrApps]] EnumDef(mods, name, tparams, template)
[nl] ‘{’ EnumCaseStat {semi EnumCaseStat ‘}’
EnumCaseStat ::= {Annotation [nl]} {Modifier} EnumCase
EnumCase ::= `case' (EnumClassDef | ObjectDef)
EnumClassDef ::= id [ClsTpeParamClause | ClsParamClause] ClassDef(mods, name, tparams, templ)
ClsParamClauses TemplateOpt
TemplateOpt ::= [‘extends’ Template | [nl] TemplateBody]
Template ::= ConstrApps [TemplateBody] | TemplateBody Template(constr, parents, self, stats)
ConstrApps ::= ConstrApp {‘with’ ConstrApp}
ConstrApp ::= AnnotType {ArgumentExprs} Apply(tp, args)
ConstrExpr ::= SelfInvocation
| ConstrBlock
SelfInvocation ::= ‘this’ ArgumentExprs {ArgumentExprs}
ConstrBlock ::= ‘{’ SelfInvocation {semi BlockStat} ‘}’
TopStatSeq ::= TopStat {semi TopStat}
TopStat ::= {Annotation [nl]} {Modifier} TmplDef
| Import
| Packaging
| PackageObject
Packaging ::= ‘package’ QualId [nl] ‘{’ TopStatSeq ‘}’ Package(qid, stats)
PackageObject ::= ‘package’ ‘object’ ObjectDef object with package in mods.
CompilationUnit ::= {‘package’ QualId semi} TopStatSeq Package(qid, stats)
```
|
