1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
|
---
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
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
| HkTypeParamClause ‘=>’ Type
| InfixType
FunArgTypes ::= InfixType
| ‘(’ [ FunArgType {‘,’ FunArgType } ] ‘)’
InfixType ::= RefinedType {id [nl] RefinedType}
RefinedType ::= WithType {[nl] Refinement}
WithType ::= AnnotType {‘with’ AnnotType}
AnnotType ::= SimpleType {Annotation}
SimpleType ::= SimpleType (TypeArgs | NamedTypeArgs)
| SimpleType ‘#’ id
| StableId
| Path ‘.’ ‘type’
| ‘(’ ArgTypes ‘)’
| ‘_’ TypeBounds
| Refinement
| SimpleLiteral
ArgTypes ::= Type {‘,’ Type}
| NamedTypeArg {‘,’ NamedTypeArg}
FunArgType ::= Type
| ‘=>’ Type
ParamType ::= [‘=>’] ParamValueType
ParamValueType ::= Type [‘*’]
TypeArgs ::= ‘[’ ArgTypes ‘]’
NamedTypeArg ::= id ‘=’ Type
NamedTypeArgs ::= ‘[’ NamedTypeArg {‘,’ NamedTypeArg} ‘]’
Refinement ::= ‘{’ [Dcl] {semi [Dcl]} ‘}’
TypeBounds ::= [‘>:’ Type] [‘<:’ Type] | INT
TypeParamBounds ::= TypeBounds {‘<%’ Type} {‘:’ Type}
Expr ::= [‘implicit’] FunParams ‘=>’ Expr
FunParams ::= Bindings
| id
| ‘_’
ExprInParens ::= PostfixExpr ‘:’ Type
| Expr
BlockResult ::= [‘implicit’] FunParams ‘=>’ Block
| Expr1
Expr1 ::= ‘if’ ‘(’ Expr ‘)’ {nl} Expr [[semi] else Expr]
| ‘if’ Expr ‘then’ Expr [[semi] else Expr]
| ‘while’ ‘(’ Expr ‘)’ {nl} Expr
| ‘while’ Expr ‘do’ Expr
| ‘do’ Expr [semi] ‘while’ Expr
| ‘try’ Expr Catches [‘finally’ Expr]
| ‘try’ Expr [‘finally’ Expr]
| ‘throw’ Expr
| ‘return’ [Expr]
| ForExpr
| [SimpleExpr ‘.’] id ‘=’ Expr
| SimpleExpr1 ArgumentExprs ‘=’ Expr
| PostfixExpr [Ascription]
| PostfixExpr ‘match’ ‘{’ CaseClauses ‘}’
Ascription ::= ‘:’ InfixType
| ‘:’ Annotation {Annotation}
Catches ::= ‘catch’ Expr
PostfixExpr ::= InfixExpr [id]
InfixExpr ::= PrefixExpr
| InfixExpr id [nl] InfixExpr
PrefixExpr ::= [‘-’ | ‘+’ | ‘~’ | ‘!’] SimpleExpr
SimpleExpr ::= ‘new’ Template
| BlockExpr
| SimpleExpr1 [‘_’]
SimpleExpr1 ::= Literal
| Path
| ‘_’
| ‘(’ ExprsInParens ‘)’
| SimpleExpr ‘.’ id
| SimpleExpr (TypeArgs | NamedTypeArgs)
| SimpleExpr1 ArgumentExprs
| XmlExpr
ExprsInParens ::= ExprInParens {‘,’ ExprInParens}
ParArgumentExprs ::= ‘(’ [ExprsInParens] ‘)’
| ‘(’ [ExprsInParens ‘,’] PostfixExpr ‘:’ ‘_’ ‘*’ ‘)’
ArgumentExprs ::= ParArgumentExprs
| [nl] BlockExpr
BlockExpr ::= ‘{’ CaseClauses ‘}’
| ‘{’ Block ‘}’
Block ::= {BlockStat semi} [BlockResult]
BlockStat ::= Import
| {Annotation} [‘implicit’ | ‘lazy’] Def
| {Annotation} {LocalModifier} TmplDef
| Expr1
|
ForExpr ::= ‘for’ (‘(’ Enumerators ‘)’ | ‘{’ Enumerators ‘}’)
{nl} [‘yield’] Expr
| ‘for’ Enumerators (‘do’ Expr | ‘yield’ Expr)
Enumerators ::= Generator {semi Enumerator | Guard}
Enumerator ::= Generator
| Guard
| Pattern1 ‘=’ Expr
Generator ::= Pattern1 ‘<-’ Expr
Guard ::= ‘if’ PostfixExpr
CaseClauses ::= CaseClause { CaseClause }
CaseClause ::= ‘case’ (Pattern [Guard] ‘=>’ Block | INT)
Pattern ::= Pattern1 { ‘|’ Pattern1 }
Pattern1 ::= PatVar ‘:’ RefinedType
| Pattern2
Pattern2 ::= [varid ‘@’] InfixPattern
InfixPattern ::= SimplePattern { id [nl] SimplePattern }
SimplePattern ::= PatVar
| Literal
| ‘(’ [Patterns] ‘)’
| XmlPattern
| SimplePattern1 [TypeArgs] [ArgumentPatterns]
SimplePattern1 ::= Path
| ‘{’ Block ‘}’
| SimplePattern1 ‘.’ id
PatVar ::= varid
| ‘_’
Patterns ::= Pattern {‘,’ Pattern}
ArgumentPatterns ::= ‘(’ [Patterns] ‘)’
| ‘(’ [Patterns ‘,’] Pattern2 ‘:’ ‘_’ ‘*’ ‘)’
```
### Type and Value Parameters
```ebnf
ClsTypeParamClause::= ‘[’ ClsTypeParam {‘,’ ClsTypeParam} ‘]’
ClsTypeParam ::= {Annotation} [{Modifier} type] [‘+’ | ‘-’]
id [HkTypeParamClause] TypeParamBounds
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} [{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
```
### Bindings and Imports
```ebnf
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 {ParArgumentExprs}
TemplateBody ::= [nl] ‘{’ [SelfType] TemplateStat {semi TemplateStat} ‘}’
TemplateStat ::= Import
| {Annotation [nl]} {Modifier} Def
| {Annotation [nl]} {Modifier} Dcl
| Expr1
SelfType ::= id [‘:’ InfixType] ‘=>’
| ‘this’ ‘:’ InfixType ‘=>’
Import ::= ‘import’ ImportExpr {‘,’ ImportExpr}
ImportExpr ::= StableId ‘.’ (id | ‘_’ | ImportSelectors)
ImportSelectors ::= ‘{’ {ImportSelector ‘,’} (ImportSelector | ‘_’) ‘}’
ImportSelector ::= id [‘=>’ id | ‘=>’ ‘_’]
```
### Declarations and Definitions
```ebnf
Dcl ::= ‘val’ ValDcl
| ‘var’ VarDcl
| ‘def’ DefDcl
| ‘type’ {nl} TypeDcl
| INT
ValDcl ::= ids ‘:’ Type
VarDcl ::= ids ‘:’ Type
DefDcl ::= DefSig [‘:’ Type]
DefSig ::= id [DefTypeParamClause] DefParamClauses
TypeDcl ::= id [TypTypeParamClause] [‘=’ Type]
| id [HkTypeParamClause] TypeBounds
Def ::= ‘val’ PatDef
| ‘var’ VarDef
| ‘def’ DefDef
| ‘type’ {nl} TypeDcl
| TmplDef
| INT
PatDef ::= Pattern2 {‘,’ Pattern2} [‘:’ Type] ‘=’ Expr
VarDef ::= PatDef
| ids ‘:’ Type ‘=’ ‘_’
DefDef ::= DefSig [‘:’ Type] ‘=’ Expr
| DefSig [nl] ‘{’ Block ‘}’
| ‘this’ DefParamClause DefParamClauses
(‘=’ ConstrExpr | [nl] ConstrBlock)
TmplDef ::= ([‘case’] ‘class’ | ‘trait’) ClassDef
| [‘case’] ‘object’ ObjectDef
ClassDef ::= id [ClsTypeParamClause]
[ConstrMods] ClsParamClauses TemplateOpt
ConstrMods ::= AccessModifier
| Annotation {Annotation} (AccessModifier | ‘this’)
ObjectDef ::= id TemplateOpt
TemplateOpt ::= [‘extends’ Template | [nl] TemplateBody]
Template ::= ConstrApps [TemplateBody] | TemplateBody
ConstrApps ::= ConstrApp {‘with’ ConstrApp}
ConstrApp ::= AnnotType {ArgumentExprs}
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
```
|
