úÎVï     (Injection of steps as conventional call 7Result of one step evaluation: either the final result 7 or an updated computation. What constitutes to a step 7 depends on the application: evaluation proceeds until  an outcome can be given. DExplicit closure for a node that expects results of a child of type m F in order to continue evaluation. The state of a node consists of the B (still needed) results of already constructed children and local  attributes. Given a node of type m) that is currently being evaluated for a  tree of type n,  Parents i m n" is the stack of its parent nodes B (that wait for values of their children to continue evaluation).  The outermost Cont1-value) is the top of the stack, i.e. the direct ( parent of the formerly mentioned node. =Computation of synthesized attributes of nonterminal of type n.  It is a trace of Info/-effects, that keeps track of the intermediate  states of the tree (using Pending), ending ultimately in the  synthesized values (using Final).  Operationally, we lift Info -values over Pending-values, thereby 7 gradually rewriting the latter, until it results in a Final. #Semantics of a nonterminal of type n as a function from inherited  attributes (Inh n) to a computation Comp i n of synthesized attributes (Syn n).  "Lazy evaluation of a computation. E Note: we cannot inspect the effect-trace, as it would sequentialize  the evaluation of children.  5One step strict evaluation. Reduction proceeds until 1 the computation is either finished or yields an Info -effect.  Unwrapper for Sem. Wrapper for final result. Wrapper for an effect. ECreate a |Pending| computation that waits for the given computation.            bf-cata-1.0Data.BreadthFirstCata.CataInjectOutcomeStepFinCompSynInhSemlazyEvaloneStepinvokefinalinforesume sem_InjectinjectNodeParentsRootContInfoFinalPending evalParents reduceParent