Scala 3 语法摘要
以下 Scala 令牌描述在引用 ASCII 片段 \u0000 – \u007F 时使用文本字符 ‘c’。
非正式描述排版为 “一些注释”。
词法语法
Scala 的词法语法由 EBNF 形式中的以下语法给出
whiteSpace ::= ‘\u0020’ | ‘\u0009’ | ‘\u000D’ | ‘\u000A’
upper ::= ‘A’ | ... | ‘Z’ | ‘$’ and any character in Unicode categories Lu, Lt or Nl,
and any character in Unicode categories Lo and Lm that doesn't have
contributory property Other_Lowercase
lower ::= ‘a’ | ... | ‘z’ | ‘_’ and any character in Unicode category Ll,
and any character in Unicode categories Lo or Lm that has contributory
property Other_Lowercase
letter ::= upper | lower
digit ::= ‘0’ | ... | ‘9’
paren ::= ‘(’ | ‘)’ | ‘[’ | ‘]’ | ‘{’ | ‘}’
delim ::= ‘`’ | ‘'’ | ‘"’ | ‘.’ | ‘;’ | ‘,’
opchar ::= ‘!’ | ‘#’ | ‘%’ | ‘&’ | ‘*’ | ‘+’ | ‘-’ | ‘/’ | ‘:’ |
‘<’ | ‘=’ | ‘>’ | ‘?’ | ‘@’ | ‘\’ | ‘^’ | ‘|’ | ‘~’
and any character in Unicode categories Sm or So
printableChar ::= all characters in [\u0020, \u007E] inclusive
UnicodeEscape ::= ‘\’ ‘u’ {‘u’} hexDigit hexDigit hexDigit hexDigit
hexDigit ::= ‘0’ | ... | ‘9’ | ‘A’ | ... | ‘F’ | ‘a’ | ... | ‘f’
charEscapeSeq ::= ‘\’ (‘b’ | ‘t’ | ‘n’ | ‘f’ | ‘r’ | ‘"’ | ‘'’ | ‘\’)
escapeSeq ::= UnicodeEscape | charEscapeSeq
op ::= opchar {opchar}
varid ::= lower idrest
boundvarid ::= varid
| ‘`’ varid ‘`’
plainid ::= alphaid
| op
id ::= plainid
| ‘`’ { charNoBackQuoteOrNewline | escapeSeq } ‘`’
idrest ::= {letter | digit} [‘_’ op]
quoteId ::= ‘'’ alphaid
spliceId ::= ‘$’ alphaid ;
integerLiteral ::= (decimalNumeral | hexNumeral) [‘L’ | ‘l’]
decimalNumeral ::= ‘0’ | digit [{digit | ‘_’} digit]
hexNumeral ::= ‘0’ (‘x’ | ‘X’) hexDigit [{hexDigit | ‘_’} hexDigit]
floatingPointLiteral
::= [decimalNumeral] ‘.’ digit [{digit | ‘_’} digit] [exponentPart] [floatType]
| decimalNumeral exponentPart [floatType]
| decimalNumeral floatType
exponentPart ::= (‘E’ | ‘e’) [‘+’ | ‘-’] digit [{digit | ‘_’} digit]
floatType ::= ‘F’ | ‘f’ | ‘D’ | ‘d’
booleanLiteral ::= ‘true’ | ‘false’
characterLiteral ::= ‘'’ (charNoQuoteOrNewline | escapeSeq) ‘'’
stringLiteral ::= ‘"’ {stringElement} ‘"’
| ‘"""’ multiLineChars ‘"""’
stringElement ::= charNoDoubleQuoteOrNewline
| escapeSeq
multiLineChars ::= {[‘"’] [‘"’] charNoDoubleQuote} {‘"’}
interpolatedString
::= alphaid ‘"’ {[‘\’] interpolatedStringPart | ‘\\’ | ‘\"’} ‘"’
| alphaid ‘"""’ {[‘"’] [‘"’] char \ (‘"’ | ‘\$’) | escape} {‘"’} ‘"""’
interpolatedStringPart
::= printableChar \ (‘"’ | ‘$’ | ‘\’) | escape
escape ::= ‘\$\$’
| ‘\$"’
| ‘\$’ alphaid
| ‘\$’ BlockExpr
alphaid ::= upper idrest
| varid
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}
可选大括号
可选大括号的原则是，任何可以跟在 { 之后的关键字也可以跟在缩进块之后，而不需要中间的 :。（允许可选 : 会适得其反，因为它会引入多种执行相同操作的方法。）
词法分析器会插入表示缩进代码区域的 indent 和 outdent 标记 在某些点。
在下面的上下文无关产生式中，我们使用符号 <<< ts >>> 来表示标记序列 ts，它要么包含在大括号对 { ts } 中，要么构成缩进区域 indent ts outdent。类似地，符号 :<<< ts >>> 表示标记序列 ts，它要么包含在大括号对 { ts } 中，要么构成缩进区域 indent ts outdent，后面跟一个 colon 标记。
colon 标记读作标准冒号 ":"，但在上下文无关语法中 colon 合法的情况下会生成它，但仅当前一个标记是字母数字标识符、反引号标识符或以下标记之一时：this、super、new、")" 和 "]"。
colon ::= ':' -- with side conditions explained above
<<< ts >>> ::= ‘{’ ts ‘}’
| indent ts outdent
:<<< ts >>> ::= [nl] ‘{’ ts ‘}’
| colon indent ts outdent
关键字
常规关键字
abstract case catch class def do else
enum export extends false final finally for
given if implicit import lazy match new
null object override package private protected return
sealed super then throw trait true try
type val var while with yield
: = <- => <: >: #
@ =>> ?=>
软关键字
as derives end extension infix inline opaque open transparent using | * + -
有关软关键字被识别的其他详细信息，请参见 关于软关键字的单独部分。
上下文无关语法
Scala 的上下文无关语法由以下 EBNF 语法给出
文字和路径
SimpleLiteral ::= [‘-’] integerLiteral
| [‘-’] floatingPointLiteral
| booleanLiteral
| characterLiteral
| stringLiteral
Literal ::= SimpleLiteral
| interpolatedStringLiteral
| symbolLiteral
| ‘null’
QualId ::= id {‘.’ id}
ids ::= id {‘,’ id}
SimpleRef ::= id
| [id ‘.’] ‘this’
| [id ‘.’] ‘super’ [ClassQualifier] ‘.’ id
ClassQualifier ::= ‘[’ id ‘]’
类型
Type ::= FunType
| HkTypeParamClause ‘=>>’ Type
| FunParamClause ‘=>>’ Type
| MatchType
| InfixType
FunType ::= FunTypeArgs (‘=>’ | ‘?=>’) Type
| HKTypeParamClause '=>' Type
FunTypeArgs ::= InfixType
| ‘(’ [ FunArgTypes ] ‘)’
| FunParamClause
FunParamClause ::= ‘(’ TypedFunParam {‘,’ TypedFunParam } ‘)’
TypedFunParam ::= id ‘:’ Type
MatchType ::= InfixType `match` <<< TypeCaseClauses >>>
InfixType ::= RefinedType {id [nl] RefinedType}
RefinedType ::= AnnotType {[nl] Refinement}
AnnotType ::= SimpleType {Annotation}
SimpleType ::= SimpleLiteral
| ‘?’ TypeBounds
| id
| Singleton ‘.’ id
| Singleton ‘.’ ‘type’
| ‘(’ Types ‘)’
| Refinement
| SimpleType1 TypeArgs
| SimpleType1 ‘#’ id
Singleton ::= SimpleRef
| SimpleLiteral
| Singleton ‘.’ id
FunArgType ::= Type
| ‘=>’ Type
FunArgTypes ::= FunArgType { ‘,’ FunArgType }
ParamType ::= [‘=>’] ParamValueType
ParamValueType ::= Type [‘*’]
TypeArgs ::= ‘[’ Types ‘]’
Refinement ::= :<<< [RefineDcl] {semi [RefineDcl]} >>>
TypeBounds ::= [‘>:’ Type] [‘<:’ Type]
TypeParamBounds ::= TypeBounds {‘:’ Type}
Types ::= Type {‘,’ Type}
表达式
Expr ::= FunParams (‘=>’ | ‘?=>’) Expr
| HkTypeParamClause ‘=>’ Expr
| Expr1
BlockResult ::= FunParams (‘=>’ | ‘?=>’) Block
| HkTypeParamClause ‘=>’ Block
| Expr1
FunParams ::= Bindings
| id
| ‘_’
Expr1 ::= [‘inline’] ‘if’ ‘(’ Expr ‘)’ {nl} Expr [[semi] ‘else’ Expr]
| [‘inline’] ‘if’ Expr ‘then’ Expr [[semi] ‘else’ Expr]
| ‘while’ ‘(’ Expr ‘)’ {nl} Expr
| ‘while’ Expr ‘do’ Expr
| ‘try’ Expr Catches [‘finally’ Expr]
| ‘try’ Expr [‘finally’ Expr]
| ‘throw’ Expr
| ‘return’ [Expr]
| ForExpr
| [SimpleExpr ‘.’] id ‘=’ Expr
| PrefixOperator SimpleExpr ‘=’ Expr
| SimpleExpr ArgumentExprs ‘=’ Expr
| PostfixExpr [Ascription]
| ‘inline’ InfixExpr MatchClause
Ascription ::= ‘:’ InfixType
| ‘:’ Annotation {Annotation}
Catches ::= ‘catch’ (Expr | ExprCaseClause)
PostfixExpr ::= InfixExpr [id] -- only if language.postfixOperators is enabled
InfixExpr ::= PrefixExpr
| InfixExpr id [nl] InfixExpr
| InfixExpr id ColonArgument
| InfixExpr MatchClause
MatchClause ::= ‘match’ <<< CaseClauses >>>
PrefixExpr ::= [PrefixOperator] SimpleExpr
PrefixOperator ::= ‘-’ | ‘+’ | ‘~’ | ‘!’ -- unless backquoted
SimpleExpr ::= SimpleRef
| Literal
| ‘_’
| BlockExpr
| ExprSplice
| Quoted
| quoteId -- only inside splices
| ‘new’ ConstrApp {‘with’ ConstrApp} [TemplateBody]
| ‘new’ TemplateBody
| ‘(’ ExprsInParens ‘)’
| SimpleExpr ‘.’ id
| SimpleExpr ‘.’ MatchClause
| SimpleExpr TypeArgs
| SimpleExpr ArgumentExprs
| SimpleExpr ColonArgument
ColonArgument ::= colon [LambdaStart]
indent (CaseClauses | Block) outdent
LambdaStart ::= FunParams (‘=>’ | ‘?=>’)
| HkTypeParamClause ‘=>’
Quoted ::= ‘'’ ‘{’ Block ‘}’
| ‘'’ ‘[’ TypeBlock ‘]’
ExprSplice ::= spliceId -- if inside quoted block
| ‘$’ ‘{’ Block ‘}’ -- unless inside quoted pattern
| ‘$’ ‘{’ Pattern ‘}’ -- when inside quoted pattern
ExprsInParens ::= ExprInParens {‘,’ ExprInParens}
ExprInParens ::= PostfixExpr ‘:’ Type
| Expr
ParArgumentExprs ::= ‘(’ [ExprsInParens] ‘)’
| ‘(’ ‘using’ ExprsInParens ‘)’
| ‘(’ [ExprsInParens ‘,’] PostfixExpr ‘*’ ‘)’
ArgumentExprs ::= ParArgumentExprs
| BlockExpr
BlockExpr ::= <<< (CaseClauses | Block) >>>
Block ::= {BlockStat semi} [BlockResult]
BlockStat ::= Import
| {Annotation {nl}} {LocalModifier} Def
| Extension
| Expr1
| EndMarker
TypeBlock ::= {TypeBlockStat semi} Type
TypeBlockStat ::= ‘type’ {nl} TypeDcl
ForExpr ::= ‘for’ ‘(’ Enumerators0 ‘)’ {nl} [‘do‘ | ‘yield’] Expr
| ‘for’ ‘{’ Enumerators0 ‘}’ {nl} [‘do‘ | ‘yield’] Expr
| ‘for’ Enumerators0 (‘do‘ | ‘yield’) Expr
Enumerators0 ::= {nl} Enumerators [semi]
Enumerators ::= Generator {semi Enumerator | Guard}
Enumerator ::= Generator
| Guard {Guard}
| Pattern1 ‘=’ Expr
Generator ::= [‘case’] Pattern1 ‘<-’ Expr
Guard ::= ‘if’ PostfixExpr
CaseClauses ::= CaseClause { CaseClause }
CaseClause ::= ‘case’ Pattern [Guard] ‘=>’ Block
ExprCaseClause ::= ‘case’ Pattern [Guard] ‘=>’ Expr
TypeCaseClauses ::= TypeCaseClause { TypeCaseClause }
TypeCaseClause ::= ‘case’ (InfixType | ‘_’) ‘=>’ Type [semi]
Pattern ::= Pattern1 { ‘|’ Pattern1 }
Pattern1 ::= PatVar ‘:’ RefinedType
| [‘-’] integerLiteral ‘:’ RefinedType
| [‘-’] floatingPointLiteral ‘:’ RefinedType
| Pattern2
Pattern2 ::= [id ‘@’] InfixPattern
InfixPattern ::= SimplePattern { id [nl] SimplePattern }
SimplePattern ::= PatVar
| Literal
| ‘(’ [Patterns] ‘)’
| Quoted
| SimplePattern1 [TypeArgs] [ArgumentPatterns]
| ‘given’ RefinedType
SimplePattern1 ::= SimpleRef
| SimplePattern1 ‘.’ id
PatVar ::= varid
| ‘_’
Patterns ::= Pattern {‘,’ Pattern}
ArgumentPatterns ::= ‘(’ [Patterns] ‘)’
| ‘(’ [Patterns ‘,’] PatVar ‘*’ ‘)’
类型和值参数
ClsTypeParamClause::= ‘[’ ClsTypeParam {‘,’ ClsTypeParam} ‘]’
ClsTypeParam ::= {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 ‘)’
| [nl] ‘(’ ‘using’ (ClsParams | FunArgTypes) ‘)’
ClsParams ::= ClsParam {‘,’ ClsParam}
ClsParam ::= {Annotation} [{Modifier} (‘val’ | ‘var’) | ‘inline’] Param
TypelessClauses ::= TypelessClause {TypelessClause}
TypelessClause ::= DefTermParamClause
| UsingParamClause
DefTypeParamClause::= [nl] ‘[’ DefTypeParam {‘,’ DefTypeParam} ‘]’
DefTypeParam ::= {Annotation} id [HkTypeParamClause] TypeParamBounds
DefTermParamClause::= [nl] ‘(’ [DefTermParams] ‘)’
UsingParamClause ::= [nl] ‘(’ ‘using’ (DefTermParams | FunArgTypes) ‘)’
DefImplicitClause ::= [nl] ‘(’ ‘implicit’ DefTermParams ‘)’
DefTermParams ::= DefTermParam {‘,’ DefTermParam}
DefTermParam ::= {Annotation} [‘inline’] Param
Param ::= id ‘:’ ParamType [‘=’ Expr]
绑定和导入
Bindings ::= ‘(’ [Binding {‘,’ Binding}] ‘)’
Binding ::= (id | ‘_’) [‘:’ Type]
Modifier ::= LocalModifier
| AccessModifier
| ‘override’
| ‘opaque’
LocalModifier ::= ‘abstract’
| ‘final’
| ‘sealed’
| ‘open’
| ‘implicit’
| ‘lazy’
| ‘inline’
AccessModifier ::= (‘private’ | ‘protected’) [AccessQualifier]
AccessQualifier ::= ‘[’ id ‘]’
Annotation ::= ‘@’ SimpleType1 {ParArgumentExprs}
Import ::= ‘import’ ImportExpr {‘,’ ImportExpr}
Export ::= ‘export’ ImportExpr {‘,’ ImportExpr}
ImportExpr ::= SimpleRef {‘.’ id} ‘.’ ImportSpec
| SimpleRef ‘as’ id
ImportSpec ::= NamedSelector
| WildCardSelector
| ‘{’ ImportSelectors) ‘}’
NamedSelector ::= id [‘as’ (id | ‘_’)]
WildCardSelector ::= ‘*’ | ‘given’ [InfixType]
ImportSelectors ::= NamedSelector [‘,’ ImportSelectors]
| WildCardSelector {‘,’ WildCardSelector}
EndMarker ::= ‘end’ EndMarkerTag -- when followed by EOL
EndMarkerTag ::= id | ‘if’ | ‘while’ | ‘for’ | ‘match’ | ‘try’
| ‘new’ | ‘this’ | ‘given’ | ‘extension’ | ‘val’
声明和定义
RefineDcl ::= ‘val’ ValDcl
| ‘def’ DefDcl
| ‘type’ {nl} TypeDcl
Dcl ::= RefineDcl
| ‘var’ VarDcl
ValDcl ::= ids ‘:’ Type
VarDcl ::= ids ‘:’ Type
DefDcl ::= DefSig ‘:’ Type
DefSig ::= id [DefTypeParamClause] [TypelessClauses] [DefImplicitClause]
TypeDcl ::= id [TypeParamClause] {FunParamClause} TypeBounds
Def ::= ‘val’ PatDef
| ‘var’ PatDef
| ‘def’ DefDef
| ‘type’ {nl} TypeDcl
| TmplDef
PatDef ::= ids [‘:’ Type] ‘=’ Expr
| Pattern2 [‘:’ Type] ‘=’ Expr
DefDef ::= DefSig [‘:’ Type] ‘=’ Expr
| ‘this’ TypelessClauses [DefImplicitClause] ‘=’ ConstrExpr
TmplDef ::= ([‘case’] ‘class’ | ‘trait’) ClassDef
| [‘case’] ‘object’ ObjectDef
| ‘enum’ EnumDef
| ‘given’ GivenDef
ClassDef ::= id ClassConstr [Template]
ClassConstr ::= [ClsTypeParamClause] [ConstrMods] ClsParamClauses
ConstrMods ::= {Annotation} [AccessModifier]
ObjectDef ::= id [Template]
EnumDef ::= id ClassConstr InheritClauses EnumBody
GivenDef ::= [GivenSig] (AnnotType [‘=’ Expr] | StructuralInstance)
GivenSig ::= [id] [DefTypeParamClause] {UsingParamClause} ‘:’ -- one of `id`, `DefTypeParamClause`, `UsingParamClause` must be present
StructuralInstance ::= ConstrApp {‘with’ ConstrApp} [‘with’ WithTemplateBody]
Extension ::= ‘extension’ [DefTypeParamClause] {UsingParamClause}
‘(’ DefTermParam ‘)’ {UsingParamClause} ExtMethods
ExtMethods ::= ExtMethod | [nl] <<< ExtMethod {semi ExtMethod} >>>
ExtMethod ::= {Annotation [nl]} {Modifier} ‘def’ DefDef
| Export
Template ::= InheritClauses [TemplateBody]
InheritClauses ::= [‘extends’ ConstrApps] [‘derives’ QualId {‘,’ QualId}]
ConstrApps ::= ConstrApp ({‘,’ ConstrApp} | {‘with’ ConstrApp})
ConstrApp ::= SimpleType1 {Annotation} {ParArgumentExprs}
ConstrExpr ::= SelfInvocation
| <<< SelfInvocation {semi BlockStat} >>>
SelfInvocation ::= ‘this’ ArgumentExprs {ArgumentExprs}
WithTemplateBody ::= <<< [SelfType] TemplateStat {semi TemplateStat} >>>
TemplateBody ::= :<<< [SelfType] TemplateStat {semi TemplateStat} >>>
TemplateStat ::= Import
| Export
| {Annotation [nl]} {Modifier} Def
| {Annotation [nl]} {Modifier} Dcl
| Extension
| Expr1
| EndMarker
|
SelfType ::= id [‘:’ InfixType] ‘=>’
| ‘this’ ‘:’ InfixType ‘=>’
EnumBody ::= :<<< [SelfType] EnumStat {semi EnumStat} >>>
EnumStat ::= TemplateStat
| {Annotation [nl]} {Modifier} EnumCase
EnumCase ::= ‘case’ (id ClassConstr [‘extends’ ConstrApps]] | ids)
TopStats ::= TopStat {semi TopStat}
TopStat ::= Import
| Export
| {Annotation [nl]} {Modifier} Def
| Extension
| Packaging
| PackageObject
| EndMarker
|
Packaging ::= ‘package’ QualId :<<< TopStats >>>
PackageObject ::= ‘package’ ‘object’ ObjectDef
CompilationUnit ::= {‘package’ QualId semi} TopStats
本文中