TOWARDS A MEANING OF LIFE? - Hassan Aït-Kaci

40 Pages·2001·2.97 MB·English

.J LOGIC GNIMMARGORP 1993:16:195-234 195
TOWARDS A GNINAEM LIFE?
NASSAH AiT-KACI AND ANDREAS IKSLEDOP
D EFIL is an latnemirepxe gnimmargorp egaugnal gnisoporp ot etargetni
eerht lanogohtro gnimmargorp paradigms nevorp lufesu rof cilobmys -moc
.noitatup morF eht s’remmargorp ,tniopdnats ti yam eb deviecrep as a
egaugnal taking retfa cigol ,gnimmargorp lanoitcnuf ,gnimmargorp and
detneiro-tcejbo .gnimmargorp morF a lamrof ,evitcepsrep ti yam eb nees
as an ecnatsni ro( ,rehtar a noitisopmoc fo eerht )secnatsni fo a tniartsnoC
cigoL gnimmargorP emehcs eud ot dlefhjiH and aklomS gninifer that fo
raffaJ and .zessaL
eW start htiw an lamrofni weivrevo gnitartsnomed EFIL as a -margorp
gnim ,egaugnal gnitartsulli woh its sevitimirp reffo rehtar unusual, and
spahrep )yltnasaelp( ,gniltrats .secneinevnoc ehT dnoces trap is a lamrof
tnuocca fo s’EFIL tcejbo noitacifinu nees as gnivlos-tniartsnoc revo cificeps
.sniamod eW dliub no krow yb aklomS and sdnuoR ot poleved -oeht-epyt
,citer ,lacigol and ciarbegla snoitidner fo a suluclac fo detros-redro erutaef
a
.snoitamixorppa
. . . the tsom tcniccus and citeop :noitinifed ‘Crber, c’est unir’ (‘To etaerc is ot .)’yfinu
sihT is a elpicnirp that tsum evah neeb at work morf the yrev gninnigeb of .efil
DARNOK ,ZNEROL Die Riickseite des Spiegeki
1. NOITCUDORTNI
sA na ,mynorca ’EFIL‘ snaem ,cigoL ,ecnatirehnI ,snoitcnuF and .snoitauqE EFIL
osla setangised an latnemirepxe gnimmargorp egaugnal dengised retfa eseht ruof
stpecerp rof gniyficeps serutcurts and .snoitatupmoc As rof what EFIL snaem as a
sihT‘ elcitra si a noisiver fo [9]. A trohs mrof fo [9] saw osla dehsilbup sa .]ol[
Address correspondence to .rD .H ,icaK-ti’A latigiD tnempiuqE ,noitaroproC hcraeseR -arobaL
,yrot 85 eunevA rotciV ,oguH 92563 nosiamlaM-lieuR ,xedeC .ecnarF :liamE Ihak,
.moc.ced.lrp@)iksledop
devieceR rebmeceD 1991; detpecca hcraM 1993.
THE JOURNAL OF LOGIC PROGRAMMING
reiveslEO ecneicS gnihsilbuP ,.oC ,.cnI 1993
655 eunevA fo eht ,saciremA weN ,kroY NY 10010 0743-1066/93/$6.00
196 .H ICAK-Tit DNA .A IKSLEDOP
gnimmargorp ,egaugnal ti is eht esoprup fo this tnemucod ot etaitini eht -atneserp
noit fo a etelpmoc lamrof scitnames rof .EFIL eW shall deecorp yb gniziretcarahc
EFIL as a cificeps noitaitnatsni fo a tniartsnoC cigoL gnimmargorP )PLC( emehcs
htiw a ralucitrap tniartsnoc .egaugnal nI its tsom evitimirp ,mrof this tniartsnoc
egaugnal setutitsnoc a cigol fo drocer serutcurts that ew shall llac detroS-redrO
erutaeF ,ro-cigol erom ,ylesicnoc FSO .cigol
nI this ,tnemucod ew naem ot od owt things: ,tsrif ew weivrevo yllamrofni eht
ytilanoitcnuf fo EFIL and eht secneinevnoc that ti sreffo rof ;gnimmargorp ,neht
ew poleved eht yratnemele lamrof snoitadnuof fo FSO .cigol eW shall llac this
FSO .cigol ,hguohtlA ni eht cisab mrof that ew evig ,ereh eht %SO msilamrof
basic
seod ton tnuocca rof all deweivrevo stcepsa fo EFIL ,.g.e( lanoitcnuf ,noitcuder
deniartsnoc tros ,)erutangis ti setutitsnoc eht lenrek ot eb dednetxe nehw ew
address esoht erom etarobale issues retal .erehwesle gniwohS woh cisab FSO cigol
stif as an tnemugra tniartsnoc egaugnal fo a PLC emehcs is erofereht a lufesu and
yrassecen .esicrexe ehT PLC emehcs that ew shall esu has neeb desoporp
yb dlefhiiH and aklomS ]51[ and is a noitazilareneg fo that eud ot raffaJ and
zessaL .]61[
eW shall enifed a class fo snoitaterpretni fo noitamixorppa serutcurts etauqeda
ot tneserper cisab EFIL .stcejbo eW llac eseht FSO .snoitaterpretni As rof ,xatnys
ew shall ebircsed eerht tnairav )redro-tsrif( :smsilamrof )1( a citeroeht-epyt mret
,egaugnal )2( an ciarbegla ,egaugnal and, )3( a lacigol )lasualc( .egaugnal llA eerht
lliw timda scitnames revo FSO snoitaterpretni .serutcurts eW shall ekam ylsuorogir
ticilpxe eht lautum citcatnys and citnames ecnelaviuqe fo eht eerht .snoitatneserper
sihT swolla us ot dehs emos thgil ,no and ,elicnocer eerht nommoc snoitaterpretni
fo elpitlum ecnatirehni as, ,ylevitcepser )1( tes ;noisulcni as )2( ciarbegla -romodne
phism; and, )3( as lacigol .noitacilpmi
ruO hcaorppa sretnec dnuora eht noiton fo an .arbegla-FSO sihT noiton was
ydaerla desu ylticilpmi ni ,l[ 21 ot evig a scitnames ot .smret-$ treG s’aklomS krow
no erutaeF cigoL ,81[ 191 edam eht msilamrof egreme erom ,ylticilpxe yllaicepse ni
eht mrof fo a lacinonac“ hparg-FSO ”,arbegla and was desu yb errGD and sdnuoR
ni tnecer krow gniwohs ytilibadicednu fo noitacifinuimes fo cilcyc serutcurts ’.]41[
sihT tnemucod is dezinagro as .swollof eW tsrif evig an lamrofni ruot fo emos fo
s’EFIL unusual gnimmargorp .secneinevnoc eW epoh yb this ot etartsulli rof eht
redaer that emos lanigiro ytilanoitcnuf is elbaliava ot a EFIL .resu eW od this yb
yaw fo small tey )yltnasaelp( gniltrats .selpmaxe gniwolloF that, ni noitceS 3, ew
deecorp htiw eht lamrof tnuocca fo cisab FSO .cigol ,erehT FSO snoitaterpretni
era decudortni rehtegot htiw citcatnys smrof fo ,smret ,sesualc and graphs taking
rieht gninaem ni esoht .snoitaterpretni tI is neht edam ticilpxe woh eseht suoirav
smrof era detaler hguorht lautum citcatnys and citnames .secnednopserroc nI
noitceS 3.4, ew wohs woh ot eit cisab FSO cigol otni a PLC .emehcs roF( eht ekas
fo making this krow ,deniatnoc-fles ew ylfeirb ,ezirammus ni xidneppA A, eht
ecnesse fo eht lareneg tniartsnoC cigoL gnimmargorP emehcs that ew esu
* errGD dna sdnuoR od ton redisnoc detros-redro shparg dna sucof ylno no ,serutaef saerehw aklomS
sredisnoc htob eht detros-redro dna eht detrosnu .esac ,revewoH aklomS seod ton ekam ticilpxe eht
mutual citcatnys dna citnames sgnippam neewteb eht ,ciarbegla ,lacigol dna citeroeht-epyt .sweiv nO eht
rehto ,dnah eht scigol deredisnoc ni [18, 191 era rehcir naht eht cisab msilamrof ot hcihw ew timil
sevlesruo ,ereh gniwolla ticilpxe noitagen dna .noitacifitnauq Naturally, all eseht snoisnetxe nac sa llew
eb deredisnoc ni our .krowemarf
TOWARDS A MEANING OF LIFE 197
.ylticilpxe tI is eud ot dlefhjiH and aklomS ).]51[ ,yllaniF ew edulcnoc gnitapicitna
no eht yrassecen snoisnetxe fo cisab FSO cigol ot eveihca a lluf gninaem fo .EFIL
2. LIFE, yllamrofnI
EFIL is a .ytinirt ehT detneiro-noitcnuf tnenopmoc fo EFIL is yltcerid devired
morf lanoitcnuf gnimmargorp languages htiw redro-rehgih snoitcnuf as ssalc-tsrif
,stcejbo data ,srotcurtsnoc and ciarbegla gnihctam-nrettap rof .gnissap-retemarap
ehT ecneinevnoc dereffo yb this elyts fo gnimmargorp is eno ni hcihw snoisserpxe
fo yna redro era ssalc-tsrif stcejbo and noitatupmoc is .etanimreted ehT -noitaler
detneiro tnenopmoc fo EFIL is yllaitnesse eno deripsni yb eht golorP egaugnal ,31[
171. noitacifinU fo redro-tsrif snrettap desu as eht gnissap-tnemugra noitarepo
turns tuo ot eb eht yek fo a etiuq euqinu and otrehtih unusual generative roivaheb
fo ,smargorp hcihw nac tcurtsnoc missing noitamrofni as dedeen ot etadommocca
.sseccus ,yllaniF eht tsom lanigiro trap fo EFIL is eht detneiro-erutcurts -opmoc
tnen hcihw stsisnoc fo a suluclac fo epyt eht-serutcurts suluclac-$ ,l[ dna--12
stnuocca rof emos fo eht )elpitlum( ecnatirehni ecneinevnoc yllacipyt dnuof ni
dellac-os detneiro-tcejbo languages.
rednU eseht ,snoitaredisnoc a larutan gnimoc ot EFIL has detsisnoc ni tsrif
gniyduts esiwriap snoitanibmoc fo hcae fo eseht eerht lanoitarepo .sloot -rohpateM
,yllaci this snaem gnizilaer segde fo a elgnairt ees( erugiF )1 erehw hcae xetrev is
emos laitnesse lanoitarepo noitidner fo eht etairporppa .suluclac NIGOL is ylpmis
golorP erehw redro-tsrif rotcurtsnoc smret evah neeb decalper yb ,smret-e htiw
epyt snoitinifed .]5[ Its lanoitarepo scitnames is eht etaidemmi noitatpada fo that fo
s’golorP DLS .noituloser eL nuF ,6[ 71 is golorP erehw noitacifinu yam ecuder
lanoitcnuf snoisserpxe otni rotcurtsnoc mrof gnidrocca ot snoitcnuf denifed yb
detneiro-nrettap lanoitcnuf .snoitacificeps ,yllaniF LOOF is ylpmis a -nrettap
detneiro lanoitcnuf egaugnal erehw redro-tsrif rotcurtsnoc smret evah neeb -er
decalp yb ,smret@ htiw epyt .snoitinifed EFIL is eht noitisopmoc fo eht eerht htiw
eht lanoitidda ytilibapac fo gniyficeps yrartibra lanoitcnuf and lanoitaler -noc
straints no stcejbo gnieb .denifed ehT txen noitcesbus sevig a yrev feirb and
lamrofni tnuocca fo eht suluclac fo epyt ecnatirehni desu ni EFIL .)suluclac-#( ehT
redaer is assumed railimaf htiw lanoitcnuf gnimmargorp and cigol .gnimmargorp
ERUGIF 1. ehT EFIL .elucelom
snoitcnuF snoitaleR
198 H. AiT-KACI AND A. PODELSKI
2.1. qKalculus
nI this ,noitces ew evig an lamrofni tub evitamrofni noitcudortni fo eht ,noitaton
,snoitarepo and ygolonimret fo eht data serutcurts fo .EFIL tI is yrassecen ot
dnatsrednu eht gnimmargorp selpmaxe ot .wollof
ehT suluclac-@ stsisnoc fo a xatnys fo derutcurts sepyt dellac smret-@ rehtegot
htiw gnipytbus and epyt noitcesretni .snoitarepo ,ylevitiutnI as dednuopxe ni ,15[
eht suluclac-@ is a ecneinevnoc rof gnitneserper ekil-drocer data serutcurts ni cigol
and lanoitcnuf gnimmargorp erom yletauqeda than redro-tsrif smret ,od tuohtiw
ssol fo eht detaicerppa-llew noitaitnatsni gniredro and noitacifinu .noitarepo
teL us ekat an elpmaxe ot .etartsulli teL us yas that eno has ni dnim ot sserpxe
yllacitcatnys a epyt erutcurts rof a person htiw eht ,ytreporp as desserpxe rof eht
denilrednu lobmys ni erugiF 2, that a niatrec lanoitcnuf margaid .setummoc
ehT xatnys fo smret-$ is eno ylpmis deroliat ot sserpxe as a mret this dnik fo
etamixorppa .noitpircsed ,suhT ni eht ,suluclac-$ eht noitamrofni fo erugiF 2 is
ylsuougibmanu dedocne otni a ,alumrof ylsuoucipsrep desserpxe as eht :mret-$
X : person(name - id@rst * string,
last - S : ,)gnirts
spouse * personhame * tsal(di * 9,
spouse = .))X
tI is tnatropmi ot distinguish gnoma eht eerht kinds fo slobmys gnitapicitrap ni a
.mret-# eW assume nevig a tes ’3 fo stros ro type constructor symbols, a tes 9 fo
spouse
ERUGIF 2. A evitatummoc lanoitcnuf .margaid
SDRAWOT A GNINAEM FO EFIL 199
,slobmys and a tes /I fo ro( nI eht
features, or attributes variables coreference tags).
mret-+ ,evoba rof ,elpmaxe eht slobmys era drawn morf 9, eht
person, id, string
slobmys morf 9, and eht slobmys X, S morf .’L eW(
name, first, fast, spouse
ezilatipac ,selbairav as ni ).golorP
A mret-+ is rehtie ro A deggat mret-$ is rehtie a elbairav ni /I
tagged untagged.
ro an noisserpxe fo eht mrof X : t erehw X E v is dellac eht s’mret root variable
and t is an deggatnu .mret-$ An deggatnu mret-$ is rehtie atomic ro attributed. An
cimota mret-G is a tros lobmys ni Y. An detubirtta mret-@ is an noisserpxe fo eht
mrof s</, =. ,,t . . . , nL * t,) erehw eht toor s’elbairav tros lobmys s ~9’ and is
dellac eht s’mret-@ ,epyt eht s’if era yllautum tcnitsid etubirtta slobmys
principal
ni Y, and eht era smret-$ .)0
ti’s (n 2
selbairaV erutpac ecnereferoc ni a esicerp .esnes yehT era ecnereferoc tags and
yam eb deweiv as depyt selbairav erehw eht epyt snoisserpxe era deggatnu .smret-$
,ecneH as a noitidnoc ot eb a mret-$ must evah all secnerrucco fo
well-fotmed,
hcae ecnereferoc tag yltnetsisnoc refer ot eht emas .erutcurts roF ,elpmaxe eht
elbairav X ni
person(id =z.n ame(first * string,
last * X : string),
father * personcid 3 name(last = X : string>>)
srefer yltnetsisnoc ot eht cimota mret-Q oT yfilpmis srettam and diova
string.
,ycnadnuder ew shall yebo a elpmis noitnevnoc fo gniyficeps eht tros fo a elbairav
at tsom ecno and dnatsrednu that rehto secnerrucco era yllauqe gnirrefer ot eht
emas ,erutcurts as :ni
person(id * name(first j string,
last * X : string),
father * person( id * name(Zast * X))).
nI ,tcaf ecnis ereht yam eb ralucric secnerefer as ni X:
person(spouse =j
this noitnevnoc is .yrassecen ,yllaniF a elbairav gniraeppa
person(spouse a X>>,
erehwon ,depyt as ni is ylticilpmi depyt yb a laiceps tsetaerg laitini
junk(kind ax)
tros lobmys syawla tneserp ni 9. sihT lobmys lliw eb tfel elbisivni and ton
T
nettirw ylticilpxe as ni ro nettirw as eht lobmys @ as
(age * integer, name =S string),
ni nI eht ,leuqes yb mret-+ ew shall syawla naem
@(age =S integer, name a string).
demrof-llew mret-@ and llac hcus a mrof a
($)-normal form.
gnizilareneG redro-tsrif ’,smret smret-r(I era deredro up ot elbairav .gnimaner
neviG that eht tes 9 is deredro-yllaitrap htiw( a tsetaerg tnemele its laitrap
T),
gniredro is dednetxe ot eht tes fo detubirtta .smret-e ,yllamrofnI a mret-+ ,t is
subsumed yb a mret-$ ,t fi )1( eht lapicnirp epyt fo ,t is a epytbus ni 9 fo eht
lapicnirp epyt fo ;,t )2( all setubirtta fo ,t era osla setubirtta fo ,t htiw smret-e
hcihw subsume rieht seugolomoh ni ;,t and, )3( all ecnereferoc stniartsnoc gnidnib
ni ,t must osla eb gnidnib ni .,t
nI‘ ,tcaf fi a redro-tsrif mret si nettirw t(f 1,. . . , t,), ti si gnihton rehto naht citcatnys ragus rof eht
mret-$ .),t,=n,...,,t*l(f
200 H. ICAK-TfA DNA .A PODELSKI
roF ,elpmaxe fi and ni 9 neht eht :mret-e
student <person paris < cityname
student(id * name@rst * string,
last * X : string),
lives-at * Y : address(city -Paris),
father * person(id * name(last *XI,
lives-at = Y 1)
is subsumed yb eht :mret-+
person(id + name(last * X : string),
lives-at * address(city * cityname),
father +. person(id * name(last =X)1).
nI ,tcaf fi eht tes 9 is hcus that )s’BLG( tsixe rof yna riap
greatest lower bounds
fo epyt ,slobmys neht eht noitpmusbus gniredro no mret-+ is osla hcus that s’BLG
.tsixe eeS( xidneppA B rof eht esac nehw s’BLG era ton ).euqinu hcuS era denifed
as eht fo owt .smret-@ A deliated noitacifinu mhtirogla rof smret-$ is
unification
nevig ni .15[
redisnoC rof elpmaxe eht tesop deyalpsid ni erugiF 3 and eht owt :smret-e
X : student(advisor = faculty(secretaly = Y : staff,
assistant =3X),
roommate 3 employee(representative * Y))
ERUGIF 3. A rewol ecittal-imes fo .stros
SDRAWOT A GNINAEM FO EFIL 102
and:
employee(advisor * f Jsecretaty * employee,
assistant - U : person),
roommate - V: studentcrepresentative * V),
helper - w,(spouse * U)).
riehT noitacifinu pu( ot tag )gnimaner sdleiy eht :mret
W : work.study(advisor - f I(secretaty * Z : workstudy(representative * Z),
assistant * WI,
roommate = Z,
helper * w,(spouse 3 WI).
tsaL ni this feirb noitcudortni ot eht ,suluclac-+/t ew nialpxe epyt .snoitinifed ehT
tpecnoc is suogolana ot what a labolg erots fo tnatsnoc snoitinifed is ni a lacitcarp
lanoitcnuf gnimmargorp egaugnal desab no .suluclac-h ehT aedi is that sepyt ni eht
erutangis yam eb deificeps ot evah setubirtta ni noitidda ot gnieb .deredro-yllaitrap
ecnatirehnI fo setubirtta morf all sepytrepus ot a epytbus is enod ni ecnadrocca
htiw mret-# noitpmusbus and .noitacifinu roF ,elpmaxe nevig a elpmis erutangis
rof eht noitacificeps fo raenil lists 9= htiw and
{list, cons, nil} nil < list cons < list,
ti is tey elbissop ot yficeps that has an etubirtta eW shall yficeps
cons tail-list.
this as:
list := {nil; cons(tai1 * list)}.
morF hcihw eht etairporppa gniredro-laitrap is .derrefni
As ni this ,elpmaxe hcus epyt snoitinifed yam eb .evisrucer ,nehT -acifinu-$
list
noit hcus a epyt noitacificeps sdeecorp yb gnidlofnu epyt slobmys -drocca
modulo
gni ot rieht .snoitinifed sihT is enod yb deen as on noisnapxe fo slobmys deen eb
enod ni esac fo )1( seruliaf eud ot citeroeht-redro sehsalc ,.g.e(
cons(tail- list)
deifinu htiw ;sliaf sevig J_ ;) )2( lobmys noitpmusbus ,.g.e( deifinu htiw
nil i.e., cons
list sevig just cons), and )3( ecnesba fo etubirtta ,.g.e( 1iat(snoc - cons) deifinu htiw
sevig ,suhT etubirtta ecnatirehni yam eb enod ”,ylizal“
cons cons( tail =j cons>).
gnivas hcum yrassecennu snoisnapxe .]ll[
nI ,EFIL a cisab mret@ setoned a lanoitcnuf noitacilppa ni s’LOOF esnes fi its
toor lobmys is a denifed .noitcnuf ,suhT a is rehtie a mret-$
functional expression
ro a noitcnujnoc fo smret-+ detoned yb ,t : ,t : 1.1 : 3.,t nA elpmaxe fo hcus is
erehw is eht LOOF noitcnuf denifed as:
append(list, L): list, append
list := {[I; [@Ilist]}.
append([ 1, L : list> -+ L.
append([HIT : list], L : list) + [HIappendCT, .l)L
nI‘ ,tcaf ew esoporp ot ees eht noitaton -:- ylpmis sa a cidayd noitarepo gnitluser ni eht BLG fo sti
stnemugra ,ecnis rof ,elpmaxe eht noitaton X: ,t : zt si dnahtrohs rof X: ,,t X: .,I erehW eht elbairav
X si ton ,yrassecen ,.ei( ton esiwrehto derahs ni eht ,)txetnoc ew yam suht ylpmis etirw ,t : .2t
202
H. AiT-KACI AND A. PODELSKI
sihT is woh lanoitcnuf ycnedneped stniartsnoc era desserpxe ni a mret-$ ni .EFIL
roF ,elpmaxe ni EFIL eht mret-$ rab(oof :X* list, baz a Y: list, fuz *
,X(dneppu )Y : list> is eno ni hcihw eht etubirtta @ is devired as a deulav-tsil
noitcnuf fo eht setubirtta rab and .zub gniyfinU hcus smret-$ sdeecorp as erofeb
oludom noisnepsus fo lanoitcnuf snoisserpxe esohw stnemugra era ton yltneiciffus
denifer ot eb ylbavorp subsumed yb snrettap fo noitcnuf .snoitinifed
As rof lanoitaler stniartsnoc no stcejbo ni ,EFIL a mret-+ t yam eb dewollof yb
a such-that esualc gnitsisnoc fo eht lacigol noitcnujnoc fo )lanoitaler( slaretil
C 1,. . . , C,,, ylbissop gniniatnoc lanoitcnuf .smret tI is nettirw as tlC,, . . . , C,. -ifinU
noitac fo hcus yllanoitaler deniartsnoc smret is enod oludom gnivorp eht deniojnoc
.stniartsnoc eW lliw etartsulli this yrev gniugirtni erutaef htiw owt :selpmaxe
prime. 1 i f e noitceS( )5.2 and quick. 1 i f e noitceS( .)4.2 nI ,tceffe this swolla
gniyficeps duemonic construints ot eb dehcatta ot .stcejbo hcuS a )demaner(
”deniartsnoc-nomead“ s’tcejbo deificeps lanoitaler and )lanoitauqe( lanoitcnuf
alumrof is dezilamron yb ,EFIL its foorp gnieb dereggirt yb noitacifinu at eht
s’tcejbo noitaerc .emit
eW evig txen emos EFIL .selpmaxe
2.2. Order-sorted logic programming: happy 1. i f e
ehT tsrif elpmaxe setartsulli a esu fo deredro-yllaitrap stros ni cigol .gnimmargorp
ehT smret-e devlovni ereh era ylno cimota ;smret-$ i.e., detubirttanu tros .slobmys
sihT elpmaxe shows eht egatnavda fo gnizirammus eht tnetxe fo a noitaler htiw
s’etaciderp stnemugra gnignar revo sepyt rehtar than .slaudividni
,reteP luaP and yraM era ,stneduts and stneduts era .snosrep
student:= {peter;paul;mary}.
student< Iperson.
sedarG era doog sedarg ro bad .sedarg A and B era doog ,sedarg elihw C, D and
F era bad .sedarg
grade:= {goodgrade;badgrade}.
goodgrade:= {a;b}.
badgrade:={c;d;f}.
sedargdooG era doog things.
goodgrade< Igoodthing.
yrevE nosrep sekil .flesreh yrevE nosrep sekil yreve doog .gniht reteP sekil
.yraM
likes(X:person,X) .
likes(person,goodthing).
likes(peter,mary).
203
SDRAWOT A GNINAEM FO EFIL
reteP tog a C, luaP an F and yraM an A.
got(peter,c) .
got(paul,f) .
got(mary,a) .
A nosrep is yppah fi eh/s tog gnihtemos that eh/s ,sekil ,ro fi eh/s sekil
gnihtemos that tog a doog .gniht
happy(X:person) :- got(x,Y),likes(X,Y).
happy(x:person) :- likes(X,Y),got(Y,goodthing).
oT eht yreuq ‘happy(X:student) ’? EFIL answers x = yram ees-eciwt(
,)?yhw neht sevig x =peter, neht .sliaf tI( spleh ot draw eht tros yhcrareih redro
).margaid
2.3. Passive constraints: 1 e fun . 1 i f e
The txen eerht selpmaxe etartsulli eht yalpretni fo noitacifinu and elbaterpretni
.snoitcnuf ehT tsrif owt od ton ekam yna cificeps esu fo .smret-q Again, eht
redro-tsrif mret noitaton is desu as ticilpmi xatnys rof smret-G htiw laciremun
.serutaef
redisnoC tsrif eht :gniwollof
P(X, Y) :- q(x, Y, Z, Z), r(X, Y).
q(X, Y, X+Y, x*Y).
q(X, Y, X+Y, (X*Y)-14).
r(3, 5).
r(2, 2).
r(4, 6).
nopU a yreuq ‘p (x, Y) ’? eht etaciderp p stceles a riap fo snoisserpxe ni X and
Y esohw snoitaulave must ,yfinu and neht stceles seulav rof X and Y. ehT tsrif
noitulos detceles yb etaciderp q sets up eht laudiser noitauqe ro( ro
residuation,
that X + Y = X * Y erom( ylesicerp that htob X + Y and X * Y dluohs
suspension)
yfinu htiw Z>, hcihw is ton deifsitas yb eht tsrif riap fo ,seulav tub is yb eht .dnoces
ehT dnoces noitulos sets up X + Y = X( * )Y - 14, hcihw is deifsitas yb X = 4,
Y= 6.
ehT txen owt selpmaxe wohs eht esu fo redro-rehgih snoitcnuf hcus as map:
map(@, [ I)-,[ I.
maP(F, [HITI) --f [F(H) Imap(F,T)l.
inc_list(N:int, L:list, map(+(N),L)).
204
H. AiT-KACI AND A. PODELSKI
Tothequely‘inc_list(3, .17,6,5,4[=LsrewsnaEFIL,‘?)L,l4,3,2,1[
nI passing, eton eht ni-tliub tnatsnoc @ as eht lavemirp EFIL tcejbo yllamrof(
nettirw T) hcihw setamixorppa gnihtyna ni eht .esrevinu
etoN that ti is ,elbissop ecnis EFIL uses smret-$ as a lasrevinu tcejbo ,erutcurts
ot pass stnemugra ot snoitcnuf yb sdrowyek and niatbo eht rewop fo laitrap
noitacilppa )gniyrruc( ni all ,stnemugra as desoppo ot suluclac-h hcihw seriuqer
thgir-ot-tfel gniyrruc .13[ roF elpmaxe fo an )evitceles-tnemugra( ,gniyrruc redisnoc
eht dettimda( )lacigolohtap EFIL :margorp
curry(V) :- V=G(2*1), G=F(X), valid(F), pick(x), p(sq(V)).
sq(X) +x*x.
twice(F,X)+F(F(X)).
valid(twice) .
P(l).
id(x) -+X.
pick(id).
What seod EFIL rewsna nehw ‘curry (v) ?' is eht ?yreuq ehT noitaler curry is
eht ytreporp fo a elbairav /I nehw this elbairav is eht tluser fo gniylppa a elbairav
noitcnuf G ot eht rebmun 1 as its dnoces .tnemugra tuB G must osla eb eht eulav
fo gniylppa a elbairav noitcnuf F ot an nwonknu tnemugra X. ehT etaciderp
valid binds F ot twice, and erofereht binds V ot twice (x, 1). ,nehT pick
binds X ot eht ytitnedi .noitcnuf ,suhT eht eulav fo ,G twice )x( , semoceb
twice (id) and V semoceb won dnuob ot 1, eht eulav fo twice (id, 1). ,yllaniF
ti must eb deifirev that eht erauqs fo /I seifinu htiw a eulav gniyfsitas ytreporp p.
2.4. Functional programming with logical variables: quick 1. i f e
sihT is a small EFIL eludom gniyficeps dna( thus, )gnitnemelpmi C.A.R. s’eraoH
kciuQ“ ”troS mhtirogla .yllanoitcnuf sihT noisrev skrow no lists hcihw era ton
detanimret htiw [ 1 )lin( tub htiw detaitnatsninu selbairav ro( yllaitrap -itnatsni
deta ot a laminim-non list .)tros ,eroferehT EFIL sekam stsil-ecnereffid bona fide
data serutcurts ni lanoitcnuf .gnimmargorp
q_sort(L,order*O) +undlist(dqsort(L,ordertiO)).
undlist(x\Y)+XIY=[ .1
dqsort([ l)+L\L.
dqsort( [HITl,order*O)
+ (~l\L2) : where
((Less,More) : split(H,T, ( [ I,[ l),order*O),
(Ll\[HIL31) : dqsort(Less ,order*O),
(L3\L2) : dqsort(More ,order*O)).
where -+ @ .