WHNF and Principal HNF

• Both principal HNF and WHNF result from Normal Order Reduction

  • Leftmost-outermost redex first (the “head” redex)

• WHNF:

  • If leftmost-outermost redex is a function, DO NOT b-reduce inside the l-body
  • Lazy Evaluation!

• Principal HNF:

  • If leftmost-outermost redex is a function, DO b -reduce inside the l-body, but apply a normal order strategy (leftmost-outermost first)

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