úÎ ó ƒ(c) Stanford University 2015 BSD-style (see the file LICENSE)ezyang@cs.stanford.edu experimentalportableSafex is an abstract data type representing data which has been evaluated to normal form. Specifically, if a value of type  aj is in weak head normal form, then it is in reduced normal form; alternatively, it is only necessary to  an  a' to assure that it is fully evaluated.For  x to preserve the  invariant, you must show that  x ==  x ( x).(c) Stanford University 2015 BSD-style (see the file LICENSE)ezyang@cs.stanford.edu experimentalportableSafeCreates a value of type F. The first time the result is evaluated to whnf, the value will be ed. To avoid this , see . Retrieves a from a value of type  a1; this value is guaranteed to be in normal form.   nf-1.0.0.1Data.NF.InternalData.NFNFUnsafeNFmakeNFgetNFghc-primGHC.Primseqdeepseq-1.3.0.2Control.DeepSeqdeepseq $fNFDataNFrnf