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---
layout: default
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
upper ::= `A' | $\cdots$ | `Z' | `$\Dollar$' | `_' $\mbox{\rm\em and Unicode category Lu}$
lower ::= `a' | $\cdots$ | `z' $\mbox{\rm\em and Unicode category Ll}$
letter ::= upper | lower $\mbox{\rm\em and Unicode categories Lo, Lt, Nl}$
digit ::= `0' | $\cdots$ | `9'
opchar ::= $\mbox{\rm\em ``all other characters in \U{0020-007F} and Unicode}$
$\mbox{\rm\em categories Sm, So except parentheses ([{}]) and periods''}$
op ::= opchar {opchar}
varid ::= lower idrest
alphaid ::= upper idrest
| varid
plainid ::= alphaid
| op
id ::= plainid
| `\`' stringLit `\`'
| INT // interpolation id, only for quasi-quotes
idrest ::= {letter | digit} [`_' op]
integerLiteral ::= (decimalNumeral | hexNumera) [`L' | `l']
decimalNumeral ::= `0' | nonZeroDigit {digit}
hexNumeral ::= `0' `x' hexDigit {hexDigit}
digit ::= `0' | nonZeroDigit
nonZeroDigit ::= `1' | $\cdots$ | `9'
octalDigit ::= `0' | $\cdots$ | `7'
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} `"'
| `"""' {[`"'] [`"'] char \ `"'} {`"'} `"""'
stringElement ::= printableChar \ (`"' | `\')
| charEscapeSeq
charEscapeSeq ::= `\b' | `\n' | `\t' | `\f' | `\r' | `"' | `'' | `\\'
processedStringLiteral
::= alphaid`"' {printableChar \ (`"' | `$') | escape} `"'
| alphaid `"""' {[`"'] [`"'] char \ (`"' | `$') | escape} {`"'} `"""'
escape ::= `$$' \comment{$}
| `$' letter { letter | digit }
| `{' Block [`;' whiteSpace stringFormat whiteSpace] `}'
stringFormat ::= {printableChar \ (`"' | `}' | ` ' | `\t' | `\n')}
whiteSpace ::= {` ' | `\t'}
symbolLiteral ::= `'' plainid
comment ::= `/*' $\mbox{\rm\em ``any sequence of characters''}$ `*/'
| `//' $\mbox{\rm\em ``any sequence of characters up to end of line''}$
nl ::= $\mbox{\rm\em ``new line character''}$
semi ::= `;' | nl {nl}
```
## Context-free Syntax
The context-free syntax of Scala is given by the following EBNF
grammar:
```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 `]'
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 | NamedTypeArgs) 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)
Expr ::= [`implicit'] FunParams `=>' Expr Function(args, expr), Function(ValDef([implicit], id, TypeTree(), EmptyTree), expr)
FunParams ::= Bindings
| id
| `_'
ExprInParens ::= PostfixExpr `:' Type
| Expr
BlockResult ::= [`implicit'] FunParams `=>' Block
| Expr1
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
| `_'
| `(' ExprsInParens2 `)' Parens(exprs)
| SimpleExpr `.' id Select(expr, id)
| SimpleExpr (TypeArgs | NamedTypeArgs) TypeApply(expr, args)
| SimpleExpr1 ArgumentExprs Apply(expr, args)
| XmlExpr
ExprsInParens ::= ExprInParens {`,' ExprInParens}
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 ForDo(enums, expr)
| `for' Enumerators (`do' Expr | `yield' 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 }
CaseClause ::= `case' (Pattern [Guard] `=>' Block | INT) CaseDef(pat, guard?, block) // block starts at =>
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 `:' `_' `*' ')
ClsTypeParamClause::= `[' ClsTypeParam {`,' ClsTypeParam} `]'
ClsTypeParam ::= {Annotation} [{Modifier} type] [`+' | `-'] TypeDef(Modifiers, name, tparams, bounds)
id [HkTypeParamClause] TypeParamBounds Bound(below, above, context)
DefTypeParamClause::= `[' DefTypeParam {`,' DefTypeParam} `]'
DefTypeParam ::= {Annotation} id [HkTypeParamClause] TypeParamBounds
TypTypeParamCaluse::= `[' 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}
[{Modifier} (`val' | `var') | `inline'] Param ValDef(mods, id, tpe, expr) -- point of mods on val/var
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 ::= `(' 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
| 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)
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'] `class' | `trait') ClassDef
| [`case'] `object' ObjectDef
ClassDef ::= id [ClsTypeParamClause] ClassDef(mods, name, tparams, templ) //
[ConstrMods] ClsParamClauses TemplateOpt 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
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
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 `}' Package(qid, stats)
PackageObject ::= `package' `object' ObjectDef object with package in mods.
CompilationUnit ::= {`package' QualId semi} TopStatSeq Package(qid, stats)
```
|
