Grammar

The syntax is a very small subset of Scala.

<Comment>      = '//' + ([^/][^/])* '//'
               | '/*' + ([^*][^/])* '*/'
               ;
               
<Name>         = [^:" {}=()\n;,*!.<>]+
               ;
             
<Actuals>      = '(' (<Expr> ,)+ <Expr> ')' | '(' <Expr> ')' | '(' ')'
               ;
             
<Arm>          = case null '=>' <Expr> | case <Name> ':' <Name> '=>' <Expr>
               ;
             
<Arms>         = '{' (<Arm> ,)+ <Arm> '}' | '{' <Arm> '}' | '{' '}'
               ;
             
<Expr>         = if '(' <Expr> ')' else <Expr>
               | while '(' <Expr> ')' <Expr>
               | match <Expr> 'with' <Arms>
               | <Name> <Actuals>
               | var <Name> '=' <Expr>
               | <Name> '=' <Expr>
               | '{' (<Expr> ';')+ <Expr> '}' | '{' <Expr> '}' | '{' '}'
               | [\d]+
               | <Name>
               | null
               | true | false
               | '(' <Expr> ')'
               | native
               | <Expr> '.' <Expr>
               | <Expr> '+' <Expr> | <Expr> '-' <Expr> | <Expr> '*' <Expr> | <Expr> '/' <Expr>
               | <Expr> '<' <Expr> | <Expr> '<=' <Expr>
               | '-' <Expr>
               | '!' <Expr>
               | <Expr> '==' <Expr> | <Expr> '!=' <Expr>
               ;

<Formal>       = <Name> ':' <Name> 
               ;
             
<Formals>      = '(' (<Formal> ';')+ <Formal> ')' | '(' (<Formal> ')' | '(' ')'
               ;

<FunctionDecl> = def <Name> <Formals> : <Name> = <Expr>
               ;

<Feature>      = <Expr> | <FunctionDecl>
               ;
             
<Features>     = '{' (<Feature> ;)+ <Feature> '}' | '{' <Feature> '}' | '{' '}'
               ;
             
<ClassDecl>    = class <Name> <Formals> Features
               | class <Name> <Formals> extends <Name> <Actuals> Features
               | class <Name> <Formals> extends native Features
               ;

There are differences between Toy and Scala.

1. Match expression in Toy: this change was needed to prevent left recursion in the parser.

// Toy
match <Expr> with <Arms>

// Scala
<Expr> match <Arms>

2. Match Arms: this change simplifies the parser.

// Toy
Arms ',' Arm | Arm

// Scala
Arms Arm | Arm

3. Semicolon separating class features (i.e. methods and expressions)

// Toy
class Foo() {
 { null } ;
 { null } 
}

// Scala
class Foo() {
 { null }
 { null } 
}