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Lexikon


Weak Head Normal Form


(WHNF) A ref="module.php?name=Lexikon&file=search&eid=1&query=lambda expression">lambda expression is in weak head normal form (WHNF) if it is a ref="module.php?name=Lexikon&file=search&eid=1&query=head normal form">head normal form (HNF) or any ref="module.php?name=Lexikon&file=search&eid=1&query=lambda abstraction">lambda abstraction. I.e. the top level is not a ref="module.php?name=Lexikon&file=search&eid=1&query=redex">redex. The term was coined by ref="module.php?name=Lexikon&file=search&eid=1&query=Simon Peyton Jones">Simon Peyton Jones to make explicit the difference between ref="module.php?name=Lexikon&file=search&eid=1&query=head normal form">head normal form (HNF) and what ref="module.php?name=Lexikon&file=search&eid=1&query=graph reduction">graph reduction systems produce in practice. A lambda abstraction with a reducible body, e.g. x . (( y . y+x) 2) is in WHNF but not HNF. To reduce this expression to HNF would require reduction of the lambda body: ( y . y+x) 2 --> 2+x Reduction to WHNF avoids the ref="module.php?name=Lexikon&file=search&eid=1&query=name capture">name capture problem with its need for ref="module.php?name=Lexikon&file=search&eid=1&query=alpha conversion">alpha conversion of an inner lambda abstraction and so is preferred in practical ref="module.php?name=Lexikon&file=search&eid=1&query=graph reduction">graph reduction systems. The same principle is often used in ref="module.php?name=Lexikon&file=search&eid=1&query=strict">strict languages such as ref="module.php?name=Lexikon&file=search&eid=1&query=Scheme">Scheme to provide ref="module.php?name=Lexikon&file=search&eid=1&query=call-by-name">call-by-name evaluation by wrapping an expression in a lambda abstraction with no arguments: D = delay E = () . E The value of the expression is obtained by applying it to the empty argument list: force D = apply D () = apply ( () . E) () = E (1994-10-31)

In addition suitable contents:
[ ref="module.php?name=Lexikon&op=content&tid=31">2 ] [ ref="module.php?name=Lexikon&op=content&tid=134">= ] [ ref="module.php?name=Lexikon&op=content&tid=178">abstraction ] [ ref="module.php?name=Lexikon&op=content&tid=262">ad ] [ ref="module.php?name=Lexikon&op=content&tid=396">ag ] [ ref="module.php?name=Lexikon&op=content&tid=411">ai ] [ ref="module.php?name=Lexikon&op=content&tid=433">al ] [ ref="module.php?name=Lexikon&op=content&tid=523">alpha conversion ] [ ref="module.php?name=Lexikon&op=content&tid=544">am ] [ ref="module.php?name=Lexikon&op=content&tid=592">an ] [ ref="module.php?name=Lexikon&op=content&tid=683">app ] [ ref="module.php?name=Lexikon&op=content&tid=740">ar ] [ ref="module.php?name=Lexikon&op=content&tid=743">arc ] [ ref="module.php?name=Lexikon&op=content&tid=759">arg ] [ ref="module.php?name=Lexikon&op=content&tid=760">argument ] [ ref="module.php?name=Lexikon&op=content&tid=800">as ] [ ref="module.php?name=Lexikon&op=content&tid=894">at ] [ ref="module.php?name=Lexikon&op=content&tid=996">av ] [ ref="module.php?name=Lexikon&op=content&tid=1026">b ] [ ref="module.php?name=Lexikon&op=content&tid=1177">bd ] [ ref="module.php?name=Lexikon&op=content&tid=1181">be ] [ ref="module.php?name=Lexikon&op=content&tid=1444">bo ] [ ref="module.php?name=Lexikon&op=content&tid=1606">bs ] [ ref="module.php?name=Lexikon&op=content&tid=1624">bt ] [ ref="module.php?name=Lexikon&op=content&tid=1695">by ] [ ref="module.php?name=Lexikon&op=content&tid=1724">ca ] [ ref="module.php?name=Lexikon&op=content&tid=1765">call-by-name ] [ ref="module.php?name=Lexikon&op=content&tid=2001">ch ] [ ref="module.php?name=Lexikon&op=content&tid=2099">ci ] [ ref="module.php?name=Lexikon&op=content&tid=2247">co ] [ ref="module.php?name=Lexikon&op=content&tid=2545">con ] [ ref="module.php?name=Lexikon&op=content&tid=2900">cu ] [ ref="module.php?name=Lexikon&op=content&tid=2976">D ] [ ref="module.php?name=Lexikon&op=content&tid=3151">de ] [ ref="module.php?name=Lexikon&op=content&tid=3371">diff ] [ ref="module.php?name=Lexikon&op=content&tid=3752">du ] [ ref="module.php?name=Lexikon&op=content&tid=3834">E ] [ ref="module.php?name=Lexikon&op=content&tid=3896">ed ] [ ref="module.php?name=Lexikon&op=content&tid=3923">edu ] [ ref="module.php?name=Lexikon&op=content&tid=3929">ee ] [ ref="module.php?name=Lexikon&op=content&tid=4148">er ] [ ref="module.php?name=Lexikon&op=content&tid=4171">es ] [ ref="module.php?name=Lexikon&op=content&tid=4199">et ] [ ref="module.php?name=Lexikon&op=content&tid=4246">evaluation ] [ ref="module.php?name=Lexikon&op=content&tid=4317">expression ] [ ref="module.php?name=Lexikon&op=content&tid=4497">fi ] [ ref="module.php?name=Lexikon&op=content&tid=4520">file ] [ ref="module.php?name=Lexikon&op=content&tid=4700">fo ] [ ref="module.php?name=Lexikon&op=content&tid=4727">for ] [ ref="module.php?name=Lexikon&op=content&tid=5057">ge ] [ ref="module.php?name=Lexikon&op=content&tid=5291">gr ] [ ref="module.php?name=Lexikon&op=content&tid=5307">graph ] [ ref="module.php?name=Lexikon&op=content&tid=5326">graph reduction ] [ ref="module.php?name=Lexikon&op=content&tid=5403">gu ] [ ref="module.php?name=Lexikon&op=content&tid=5434">h ] [ ref="module.php?name=Lexikon&op=content&tid=5540">hat ] [ ref="module.php?name=Lexikon&op=content&tid=5768">hr ] [ ref="module.php?name=Lexikon&op=content&tid=5931">id ] [ ref="module.php?name=Lexikon&op=content&tid=5986">iff ] [ ref="module.php?name=Lexikon&op=content&tid=6013">il ] [ ref="module.php?name=Lexikon&op=content&tid=6064">in ] [ ref="module.php?name=Lexikon&op=content&tid=6068">inc ] [ ref="module.php?name=Lexikon&op=content&tid=6413">io ] [ ref="module.php?name=Lexikon&op=content&tid=6449">ir ] [ ref="module.php?name=Lexikon&op=content&tid=6482">is ] [ ref="module.php?name=Lexikon&op=content&tid=6558">it ] [ ref="module.php?name=Lexikon&op=content&tid=6589">J ] [ ref="module.php?name=Lexikon&op=content&tid=6789">ke ] [ ref="module.php?name=Lexikon&op=content&tid=6918">la ] [ ref="module.php?name=Lexikon&op=content&tid=6938">lambda abstraction ] [ ref="module.php?name=Lexikon&op=content&tid=6940">lambda expression ] [ ref="module.php?name=Lexikon&op=content&tid=6950">language ] [ ref="module.php?name=Lexikon&op=content&tid=7014">lc ] [ ref="module.php?name=Lexikon&op=content&tid=7023">ld ] [ ref="module.php?name=Lexikon&op=content&tid=7091">Lex ] [ ref="module.php?name=Lexikon&op=content&tid=7107">li ] [ ref="module.php?name=Lexikon&op=content&tid=7220">list ] [ ref="module.php?name=Lexikon&op=content&tid=7415">lu ] [ ref="module.php?name=Lexikon&op=content&tid=7441">ly ] [ ref="module.php?name=Lexikon&op=content&tid=7463">ma ] [ ref="module.php?name=Lexikon&op=content&tid=8032">mo ] [ ref="module.php?name=Lexikon&op=content&tid=8040">mod ] [ ref="module.php?name=Lexikon&op=content&tid=8079">module ] [ ref="module.php?name=Lexikon&op=content&tid=8167">mp ] [ ref="module.php?name=Lexikon&op=content&tid=8228">ms ] [ ref="module.php?name=Lexikon&op=content&tid=8384">N ] [ ref="module.php?name=Lexikon&op=content&tid=8386">na ] [ ref="module.php?name=Lexikon&op=content&tid=8396">name capture ] [ ref="module.php?name=Lexikon&op=content&tid=8460">nc ] [ ref="module.php?name=Lexikon&op=content&tid=8472">ne ] [ ref="module.php?name=Lexikon&op=content&tid=8627">ng ] [ ref="module.php?name=Lexikon&op=content&tid=8672">nn ] [ ref="module.php?name=Lexikon&op=content&tid=8675">no ] [ ref="module.php?name=Lexikon&op=content&tid=8718">norm ] [ ref="module.php?name=Lexikon&op=content&tid=8720">normal form ] [ ref="module.php?name=Lexikon&op=content&tid=9014">op ] [ ref="module.php?name=Lexikon&op=content&tid=9550">ph ] [ ref="module.php?name=Lexikon&op=content&tid=9616">ping ] [ ref="module.php?name=Lexikon&op=content&tid=9651">pl ] [ ref="module.php?name=Lexikon&op=content&tid=9738">ply ] [ ref="module.php?name=Lexikon&op=content&tid=9908">pr ] [ ref="module.php?name=Lexikon&op=content&tid=10144">pt ] [ ref="module.php?name=Lexikon&op=content&tid=10253">query ] [ ref="module.php?name=Lexikon&op=content&tid=10364">rc ] [ ref="module.php?name=Lexikon&op=content&tid=10385">re ] [ ref="module.php?name=Lexikon&op=content&tid=10440">Red ] [ ref="module.php?name=Lexikon&op=content&tid=10444">redex ] [ ref="module.php?name=Lexikon&op=content&tid=10453">reduction ] [ ref="module.php?name=Lexikon&op=content&tid=10767">ro ] [ ref="module.php?name=Lexikon&op=content&tid=10918">S ] [ ref="module.php?name=Lexikon&op=content&tid=10922">sa ] [ ref="module.php?name=Lexikon&op=content&tid=10959">sam ] [ ref="module.php?name=Lexikon&op=content&tid=11047">Scheme ] [ ref="module.php?name=Lexikon&op=content&tid=11150">se ] [ ref="module.php?name=Lexikon&op=content&tid=11376">si ] [ ref="module.php?name=Lexikon&op=content&tid=11651">so ] [ ref="module.php?name=Lexikon&op=content&tid=11934">st ] [ ref="module.php?name=Lexikon&op=content&tid=12090">strict ] [ ref="module.php?name=Lexikon&op=content&tid=12133">su ] [ ref="module.php?name=Lexikon&op=content&tid=12246">sy ] [ ref="module.php?name=Lexikon&op=content&tid=12312">system ] [ ref="module.php?name=Lexikon&op=content&tid=12359">T ] [ ref="module.php?name=Lexikon&op=content&tid=12588">th ] [ ref="module.php?name=Lexikon&op=content&tid=12721">to ] [ ref="module.php?name=Lexikon&op=content&tid=12787">tr ] [ ref="module.php?name=Lexikon&op=content&tid=12939">tw ] [ ref="module.php?name=Lexikon&op=content&tid=12986">ua ] [ ref="module.php?name=Lexikon&op=content&tid=13030">um ] [ ref="module.php?name=Lexikon&op=content&tid=13175">us ] [ ref="module.php?name=Lexikon&op=content&tid=13252">va ] [ ref="module.php?name=Lexikon&op=content&tid=13260">value ] [ ref="module.php?name=Lexikon&op=content&tid=13310">ve ] [ ref="module.php?name=Lexikon&op=content&tid=13335">version ] [ ref="module.php?name=Lexikon&op=content&tid=13366">vi ] [ ref="module.php?name=Lexikon&op=content&tid=13703">WHNF ] [ ref="module.php?name=Lexikon&op=content&tid=14075">yt ]






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