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|
{-
This example demonstrates the use of error correction. A closing brace
is automatically inserted if it is missing.
frown --debug Light.g
frown --debug --trace Light.g
Try
decls [LBRACE, Var, EQU, Var, EOF] :: IO ()
expr [Var, LPAR, LET, LBRACE, Var, EQU, Var, IN, Var, RPAR, EOF] :: IO ()
-}
module Light
where
import Monad
type Result = Maybe
%{
Terminal = LBRACE
| RBRACE
| SEMICOLON
| EQU
| LET
| IN
| LPAR
| RPAR
| Var
| *EOF;
Nonterminal = *decls
| declList
| decl
| close
| *expr
| fexpr
| aexpr;
decls : LBRACE, declList, close;
declList : declList, SEMICOLON, decl;
| declList, SEMICOLON;
| decl;
| ;
decl : Var, EQU, expr;
close : RBRACE;
| insert RBRACE;
expr : LET, decls, IN, expr;
| fexpr;
fexpr : fexpr, aexpr;
| aexpr;
aexpr : Var;
| LPAR, expr, RPAR;
}%
data Terminal = LBRACE
| RBRACE
| SEMICOLON
| EQU
| LET
| IN
| LPAR
| RPAR
| Var
| EOF
deriving (Show)
frown _ = fail "syntax error"
|
