This is a flashcard version of Rats! original documentation. Refer there for more details.

Rats! Body

Intro         <- ModuleDecl Dependency* Header? Body? Footer? Option?

Rats! Syntax

Production    <- Full / Addition / Removal / Override
Full          <- PAttributes QName Identifier EQUAL Choice SEMICOLON
Addition      <- QName Identifier PLUSEQUAL
                 ( SName ELLIPSIS SLASH Choice SEMICOLON
                 / Choice SLASH SName ELLIPSIS SEMICOLON )
Removal       <- QName Identifier MINUSEQUAL
                 SName ( COMMA SName )* SEMICOLON
Override      <- QName Identifier COLONEQUAL Choice SEMICOLON
                 / QName Identifier COLONEQUAL ELLIPSIS SLASH Choice SEMICOLON
                 / QName Identifier COLONEQUAL Choice SLASH ELLIPSIS SEMICOLON
                 / PAttributes QName Identifier COLONEQUAL ELLIPSIS SEMICOLON
PAttributes   <- &(QName Identifier EQUAL) / Attribute PAttributes
Choice        <- Sequence (SLASH Sequence)*
Sequence      <- !(SName ELLIPSIS / ELLIPSIS) SName? Voided*
Voided        <- ("void" Spacing COLON)? Prefix
Prefix        <- (AND / NOT / CARET / Identifier COLON
                 / StringLit Spacing COLON)? Suffix
Suffix        <- Primary (QUESTION / STAR / PLUS)?
Primary       <- QName / Literal / Action / OPEN Choice CLOSE

Action        <- '{' ActionBody* '}' Spacing
ActionBody    <- Action / CharLit / StringLit / MLComment / SLComment / !'}' .

Attribute     <- Identifier (OPEN AttValue CLOSE)?
AttValue      <- Integer / QName / StringLit Spacing

Remarks and common pitfalls

In principle, a text-only production is one whose semantic value equals the matched text. In practice, the compiler recognizes a production as text-only if (a) it returns String by definition, (b) it does not have assign any value to yyValue, and (c) it references only text-only (or void) productions
Every production which is not genric, text-only or void must have a semantic action that assigns to yyValue
A choice that references a production that always succeeds, must have this reference at the end of the choice. Otherwise, incorrect code is generated, and possibly an error message returned


Comment	*/ comment / // comment*
Character literal	`'a'`
String literal	`"hello"`
Escape sequence	`\n, \\, \u00ff, \[, \-, \]`
Any character constant	`_`
Character class, grouping	`[], ()`
Option operator, zero-or-more and one-or-more operators	`?,*,+`
Matching syntactic predicate	transient void Directive = [#] [ ] line:DecimalConstant [ ] ["] file:FileName ["] f1:" 1"? f2:" 2"? f3:" 3"? f4:" 4"? &LineTerminator { yyState.lineMarker(line, file, f1, f2, f3, f4); } / [#] Space* "pragma " pragma:Pragma &LineTerminator { yyState.pragma(pragma); } / [#] Space* "ident" Space+ s:StringLiteral &LineTerminator { yyState.ident(s); } / /* Empty */ ;
Not matching syntactic predicate	transient String Pragma = ( ![\n\r] _ )* ;
Semantic predicate	generic AbstractDeclarator = p:Pointer? d:DirectAbstractDeclarator &{ (null != p) \|\| (null != d) } ;
Semantic predicate	`generic String Keyword = vtext:Identifier &{ "begin".equals (vtext) }`
Voiding operator	generic ParameterList = ParameterDeclaration (void:",":Symbol ParameterDeclaration)* ;
Parser actions	public String ByteString = n:Integer ':' ^{ yyResult = parseChars(n, yyStart, yyBase); } ;
Production, binding, and Text-matching expression	public FullProduction FullProduction = atts : ProductionAttributes type : Name nt : UnqualifiedNonTerminal "=" : Symbol choice : Choice ";" : Symbol { yyValue = new FullProduction (atts.list (), type, nt, choice); }
Passing the semantic value through	Action Header = "header":Word yyValue:Action ;
Options, repetitions and nested choices	/ '[' l:( c1:ClassChar '-' c2:ClassChar { yyValue = new CharRange(Utilities.unescape(c1).charAt(0), Utilities.unescape(c2).charAt(0)); } / c1:ClassChar { yyValue = new CharRange(Utilities.unescape(c1).charAt(0)); } )* ']' Spacing { yyValue = new CharClass(l.list()); }
Generic type	generic LogicalAndExpression = LogicalAndExpression void:"&&":Symbol BitwiseOrExpression / BitwiseOrExpression ;
Void and text-only productions Transient productions	transient void Spacing = (Space / LineTerminator / TraditionalComment/ EndOfLineComment)* ;
Void and text-only productions Transient productions	String Symbol = SymbolCharacters Spacing ;

Rats! Module

ModuleDecl    <- "module" FSpacing ModuleRef SEMICOLON
Dependency    <- Modification / Instantiation / Import
Modification  <- "modify" FSpacing ModuleRef ModuleTarget? SEMICOLON
Instantiation <- "instantiate" FSpacing ModuleRef ModuleTarget? SEMICOLON
Import        <- "import" FSpacing ModuleRef ModuleTarget? SEMICOLON
ModuleRef     <- QName ModuleParams?
ModuleParams  <- OPEN ( QName (COMMA QName)* )? CLOSE
ModuleTarget  <- "as" FSpacing QName

Rats! Global Actions and Options

Header        <- "header" Spacing Action
Body          <- "body" Spacing Action
Footer        <- "footer" Spacing Action
Option        <- "option" FSpacing Attribute (COMMA Attribute)* SEMICOLON

Rats! Lexer

QName         <- Id ('.' Id)* Spacing
SName         <- LESS Id GREATER
Identifier    <- Id Spacing
Id            <- [a-zA-Z] [a-zA-Z0-9]*

Literal       <- ('_' / CharLit / StringLit / Class) Spacing
CharLit       <- ['] (Escape / !['\\] .)  [']
StringLit     <- ["] (Escape / !["\\] .)* ["]
Class         <- '[' (Char '-' Char / Char)* ']'
Char          <- Escape / ![-\]\\] .
Escape        <- '\\' [btnfr"'\[\\\]-] / '\\' 'u' HexQuad / OctalEscape
OctalEscape   <- '\\' ([0-3] OctDigit OctDigit / OctDigit OctDigit / OctDigit)

Integer       <- (HexNumber / OctNumber / Number) Spacing
HexNumber     <- '0' [xX] HexDigit+
HexQuad       <- HexDigit HexDigit HexDigit HexDigit
HexDigit      <- [0-9a-fA-F]
Number        <- '0' / NZDigit Digit*
NZDigit       <- [1-9]
Digit         <- [0-9]
OctNumber     <- '0' OctDigit+
OctDigit      <- [0-7]

ELLIPSIS      <- "..." Spacing
PLUSEQUAL     <- "+=" Spacing
MINUSEQUAL    <- "-=" Spacing
COLONEQUAL    <- ":=" Spacing
COMMA         <- ',' Spacing
EQUAL         <- '=' Spacing
SLASH         <- '/' ![/*] Spacing
AND           <- '&' Spacing
NOT           <- '!' Spacing
CARET         <- '^' Spacing
COLON         <- ':' Spacing
QUESTION      <- '?' Spacing
STAR          <- '*' Spacing
PLUS          <- '+' Spacing
OPEN          <- '(' Spacing
CLOSE         <- ')' Spacing
SEMICOLON     <- ';' Spacing
LESS          <- '<'
GREATER       >- '>' Spacing

Spacing       <- (Space / SLComment / MLComment)*
FSpacing      <- (Space / SLComment / MLComment)+
Space         <- ' ' / '\t' / '\f' / EOL
SLComment     <- "//" (![\n\r] .)* EOL
MLComment     <- "/*" ('*' !'/' / !'*' .)* "*/"
EOL           <- '\r' '\n' / '\r' / '\n'
EOF           <- !.