visitor.sig

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signature VISITOR = sig

type RESULT

datatype NEXT = Stop of RESULT (* abort the traversal *)
              | Skip of RESULT (* continue traversal but skip children *)
              | Cont of RESULT (* continue traversal, including children *)

type 'a METHOD = 'a * RESULT -> NEXT

type VISITOR = { visitExpr : Ast.EXPRESSION METHOD,
                 visitStmt : Ast.STATEMENT METHOD,
                 visitDefn : Ast.DEFN METHOD,
                 visitFunc : Ast.FUNC METHOD }

val withVisitExpr : VISITOR * Ast.EXPRESSION METHOD -> VISITOR
val withVisitStmt : VISITOR * Ast.STATEMENT METHOD -> VISITOR
val withVisitDefn : VISITOR * Ast.DEFN METHOD -> VISITOR
val withVisitFunc : VISITOR * Ast.FUNC METHOD -> VISITOR

val default : VISITOR

val stop : 'a METHOD
val skip : 'a METHOD
val cont : 'a METHOD

val foldExpr : VISITOR * Ast.EXPRESSION * RESULT -> RESULT
val foldStmt : VISITOR * Ast.STATEMENT * RESULT -> RESULT
val foldDefn : VISITOR * Ast.DEFN * RESULT -> RESULT
val foldFunc : VISITOR * Ast.FUNC * RESULT -> RESULT

end