Concrete Syntax

rascal-0.40.17

Synopsis

The concrete syntax of Func.

Examples

module demo::lang::Func::Func

lexical Ident =  [a-zA-Z][a-zA-Z0-9]* !>> [a-zA-Z0-9];

lexical Natural = [0-9]+ !>> [0-9];

lexical LAYOUT = [\t-\n\r\ ];

layout LAYOUTLIST = LAYOUT*  !>> [\t-\n\r\ ] ;

start syntax Prog = prog: Func* ;

syntax Func = func: Ident name "(" {Ident ","}* ")" "=" Exp;

syntax Exp 
    = let: "let" {Binding ","}* "in" Exp "end"
    | cond: "if" Exp "then" Exp "else" Exp "end"
    | bracket "(" Exp ")"
    | var: Ident
    | nat: Natural 
    | call: Ident "(" {Exp ","}* ")"
    | address: "&" Ident
    > deref: "*" Exp 
    > non-assoc (
        left mul: Exp "*" Exp 
      | non-assoc div: Exp "/" Exp
    ) 
    > left (
        left add: Exp "+" Exp 
      | left sub: Exp "-" Exp
    )
    >
    non-assoc (
        non-assoc gt: Exp "\>" Exp
      | non-assoc lt:  Exp "\<" Exp
      | non-assoc geq:  Exp "\>=" Exp
      | non-assoc leq:  Exp "\<=" Exp
    )
    >
    right assign: Exp ":=" Exp
    >
    right seq: Exp ";" Exp
    ; 

syntax Binding = binding: Ident "=" Exp;

The concrete syntax of Func uses many features of Rascal's syntax definitions. Some notes:

• The definition of lexical syntax follows the pattern: Define lexical symbols (Ident, Natural). Define rules for layout. ** Use follow restrictions (!>>) to enforce the longest match of lexical symbols.
• The definition of lexical also follows a common pattern: List of non-terminal is defined with their alternatives. One non-terminal is designated as start symbol (Prog). Each alternative has a label, this is for the benefit of converting parse trees to abstract syntaxt trees. Each alternative spells out its priority and associativity.