Oz is an attempt to create a high-level concurrent programming language providing the problem solving capabilities of logic programming (i.e., constraints and search). Its computation model can be seen as a rather radical extension of the concurrent constraint model providing for higher-order programming, deep guards, state, and encapsulated search. This paper focuses on the most recent extension, a higher-order combinator providing for encapsulated search. The search combinator spawns a local computation space and resolves remaining choices by returning the alternatives as rst-class citizens. The search combinator allows to program di erent search strategies, including depth-rst, indeterministic one solution, demand-driven multiple solution, all solutions, and best solution (branch and bound) search. The paper also discusses the semantics of integer and nite domain constraints in a deep guard computation model.
St.uhlsat.zf' nh a uswf' g 3 , 0-6600 S a arbrii cken , Germ a ny E-m a il : {s m o lka. hf. nz. wU f' rt.z} @dfki .uni-sh .d l' Abstl'act Oz is a n f' Xl)f' rill lf' nt.al hig hf' r-o rdf'r concurrf' nt. cons t.r a int. p rogrammin g syst.f' m IInd f' r df'w lop lll f' nt. a t, DFKI. It. cOl llhin es id f'as fr o lll log ic a nd con curre nt. prog ra mmill g in a s impl f' yf' t. f'xpl't~ss iv l' la ng ll a gl'. Fro lll logic prog ra lllluin g Oz inh f' rit.s log ic vari a bll's a nd logi c d at.a st.rur.t.llI'f'S, whi ch prov idf' fo r a progr a mmiu g s t.y lf' wllf' re pa rt.i a l info l'lw\,t.i o n a ho llt. tl lf' va lllf's of va ri a bl f's is imp mw d concurrf' nt.I y a nd in Cl'f'll w nt.ally. A now l ff'a t.lIl'f' of Oz is t.h a t. it. accommo d a t.es h ig hf' r-ordf' r p rogra mmin g wit.h o ut. sacr ificin g t.h a t. d pll o t.at.i o n a nd equ a lit.y of va ri a hlf's cu I' capt.llrf' d hy first.-ord f' r logic. All o t.h e r Ile w fl'at. llrp of O z is cons t.r a int. commtlllicat.ion , a nf' W fo rm of asyn chro no us communi cat.i o n I'x plo it.in g log ic vari a bl l's. COlls t.r a int. co mmuni cat.i o n a vo id s t.h p p ro hl pm s o f st. rl'am commllni cat.io n , Ut I' convent.io ll a l commllni cat.i o ll m echanism Pll1pl oyed in CO Il CIIITI' Il t. log ic p rog ra mming. Cons t.r a int. comllllllli cat.i o n call I)f' Sf'f' 1l as prov idill g a minim a l fo rlll o f st. a t.1' full y comp a t.ihll' wit.h log ic d a t. a s t.nt c.t. ures. Basl'd o n cons t.r a int. communi cat.i o n a nd high er-order p rog ra mllling, Oz readily s upp o rt.s a va riet.y of o hj l'd-orient.Pd progra mmillg st.yl l's incllldillg mlllt.iplf' inherit.a ll cl'.
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