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Diffstat (limited to 'spec/01-lexical-syntax.md')
| -rw-r--r-- | spec/01-lexical-syntax.md | 60 |
1 files changed, 24 insertions, 36 deletions
diff --git a/spec/01-lexical-syntax.md b/spec/01-lexical-syntax.md index ef1f2bf053..4bfef79ac5 100644 --- a/spec/01-lexical-syntax.md +++ b/spec/01-lexical-syntax.md @@ -11,7 +11,7 @@ Scala programs are written using the Unicode Basic Multilingual Plane presently supported. This chapter defines the two modes of Scala's lexical syntax, the Scala mode and the _XML mode_. If not otherwise mentioned, the following descriptions of Scala tokens refer -to _Scala mode_, and literal characters ‘c’ refer to the ASCII fragment +to _Scala mode_, and literal characters ‘c’ refer to the ASCII fragment `\u0000` – `\u007F`. In Scala mode, _Unicode escapes_ are replaced by the corresponding @@ -29,7 +29,7 @@ but I can't make it work nor can I imagine how this would make sense, so I removed it for now. --> -To construct tokens, characters are distinguished according to the following +To construct tokens, characters are distinguished according to the following classes (Unicode general category given in parentheses): 1. Whitespace characters. `\u0020 | \u0009 | \u000D | \u000A`. @@ -41,13 +41,13 @@ classes (Unicode general category given in parentheses): 1. Parentheses `‘(’ | ‘)’ | ‘[’ | ‘]’ | ‘{’ | ‘}’ `. 1. Delimiter characters ``‘`’ | ‘'’ | ‘"’ | ‘.’ | ‘;’ | ‘,’ ``. 1. Operator characters. These consist of all printable ASCII characters - `\u0020` - `\u007F` which are in none of the sets above, mathematical + `\u0020` - `\u007F` which are in none of the sets above, mathematical symbols (`Sm`) and other symbols (`So`). ## Identifiers ```ebnf -op ::= opchar {opchar} +op ::= opchar {opchar} varid ::= lower idrest plainid ::= upper idrest | varid @@ -61,14 +61,14 @@ There are three ways to form an identifier. First, an identifier can start with a letter which can be followed by an arbitrary sequence of letters and digits. This may be followed by underscore ‘_’ characters and another string composed of either letters and digits or -of operator characters. Second, an identifier can start with an operator +of operator characters. Second, an identifier can start with an operator character followed by an arbitrary sequence of operator characters. The preceding two forms are called _plain_ identifiers. Finally, an identifier may also be formed by an arbitrary string between back-quotes (host systems may impose some restrictions on which strings are legal for identifiers). The identifier then is composed of all characters excluding the backquotes themselves. - + As usual, a longest match rule applies. For instance, the string ```scala @@ -92,8 +92,8 @@ do else extends false final finally for forSome if implicit import lazy match new null object override package private protected -return sealed super this throw -trait try true type val +return sealed super this throw +trait try true type val var while with yield _ : = => <- <: <% >: # @ ``` @@ -115,7 +115,6 @@ For instance, the statement `Thread.yield()` is illegal, since `yield` is a reserved word in Scala. However, here's a work-around: `` Thread.`yield`() `` - ## Newline Characters ```ebnf @@ -134,7 +133,7 @@ The tokens that can terminate a statement are: literals, identifiers and the following delimiters and reserved words: ```scala -this null true false return type <xml-start> +this null true false return type <xml-start> _ ) ] } ``` @@ -142,8 +141,8 @@ The tokens that can begin a statement are all Scala tokens _except_ the following delimiters and reserved words: ```scala -catch else extends finally forSome match -with yield , . ; : = => <- <: <% +catch else extends finally forSome match +with yield , . ; : = => <- <: <% >: # [ ) ] } ``` @@ -169,7 +168,7 @@ Newlines are disabled in: 1. Any regions analyzed in [XML mode](#xml-mode). Note that the brace characters of `{...}` escapes in XML and -string literals are not tokens, +string literals are not tokens, and therefore do not enclose a region where newlines are enabled. @@ -189,14 +188,14 @@ Multiple newline tokens are accepted in the following places (note that a semicolon in place of the newline would be illegal in every one of these cases): -- between the condition of a +- between the condition of a [conditional expression](06-expressions.html#conditional-expressions) or [while loop](06-expressions.html#while-loop-expressions) and the next following expression, -- between the enumerators of a +- between the enumerators of a [for-comprehension](06-expressions.html#for-comprehensions-and-for-loops) and the next following expression, and -- after the initial `type` keyword in a +- after the initial `type` keyword in a [type definition or declaration](04-basic-declarations-and-definitions.html#type-declarations-and-type-aliases). A single new line token is accepted @@ -300,16 +299,15 @@ illegal). protected class Data { ... } ``` - ## Literals There are literals for integer numbers, floating point numbers, characters, booleans, symbols, strings. The syntax of these literals is in each case as in Java. -<!-- TODO +<!-- TODO say that we take values from Java, give examples of some lits in - particular float and double. + particular float and double. --> ```ebnf @@ -322,11 +320,10 @@ Literal ::= [‘-’] integerLiteral | ‘null’ ``` - ### Integer Literals ```ebnf -integerLiteral ::= (decimalNumeral | hexNumeral | octalNumeral) +integerLiteral ::= (decimalNumeral | hexNumeral | octalNumeral) [‘L’ | ‘l’] decimalNumeral ::= ‘0’ | nonZeroDigit {digit} hexNumeral ::= ‘0’ ‘x’ hexDigit {hexDigit} @@ -356,14 +353,12 @@ is _pt_. The numeric ranges given by these types are: |`Short` | $-2\^{15}$ to $2\^{15}-1$| |`Char` | $0$ to $2\^{16}-1$ | - ### Example ```scala 0 21 0xFFFFFFFF -42L ``` - ### Floating Point Literals ```ebnf @@ -410,7 +405,6 @@ booleanLiteral ::= ‘true’ | ‘false’ The boolean literals `true` and `false` are members of type `Boolean`. - ### Character Literals ```ebnf @@ -433,7 +427,6 @@ character `\u000A` (line feed) is not a printable character. One can use instead the escape sequence `'\n'` or the octal escape `'\12'` ([see here](#escape-sequences)). - ### String Literals ```ebnf @@ -446,7 +439,7 @@ characters are either printable unicode character or are described by [escape sequences](#escape-sequences). If the string literal contains a double quote character, it must be escaped, i.e. `"\""`. The value of a string literal is an instance of -class `String`. +class `String`. ### Example @@ -500,17 +493,16 @@ evaluates to ```scala the present string -spans three +spans three lines. ``` Method `stripMargin` is defined in class -[scala.collection.immutable.StringLike](http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.StringLike). +[scala.collection.immutable.StringLike](http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.StringLike). Because there is a predefined [implicit conversion](06-expressions.html#implicit-conversions) from `String` to `StringLike`, the method is applicable to all strings. - ### Escape Sequences The following escape sequences are recognized in character and string literals. @@ -526,7 +518,6 @@ The following escape sequences are recognized in character and string literals. | `‘\‘ ‘'‘` | `\u0027` | single quote | `'` | | `‘\‘ ‘\‘` | `\u005c` | backslash | `\` | - A character with Unicode between 0 and 255 may also be represented by an octal escape, i.e. a backslash `'\'` followed by a sequence of up to three octal characters. @@ -534,7 +525,6 @@ sequence of up to three octal characters. It is a compile time error if a backslash character in a character or string literal does not start a valid escape sequence. - ### Symbol literals ```ebnf @@ -557,7 +547,6 @@ caches weak references to `Symbol`s, thus ensuring that identical symbol literals are equivalent with respect to reference equality. - ## Whitespace and Comments Tokens may be separated by whitespace characters @@ -572,7 +561,6 @@ but are required to be properly nested. Therefore, a comment like `/* /* */` will be rejected as having an unterminated comment. - ## XML mode In order to allow literal inclusion of XML fragments, lexical analysis @@ -589,10 +577,10 @@ brace and immediately followed by a character starting an XML name. The scanner switches from XML mode to Scala mode if either -- the XML expression or the XML pattern started by the initial ‘<’ has been +- the XML expression or the XML pattern started by the initial ‘<’ has been successfully parsed, or if -- the parser encounters an embedded Scala expression or pattern and - forces the Scanner +- the parser encounters an embedded Scala expression or pattern and + forces the Scanner back to normal mode, until the Scala expression or pattern is successfully parsed. In this case, since code and XML fragments can be nested, the parser has to maintain a stack that reflects the nesting |