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Section 4

Section 4. CSE 341 – Patrick Larson. Mutual Recursion. What if we need function f to call g, a nd function g to call f?. Mutual Recursion. Does this work? 1 fun f x = 5 fun g y = 2 ... 6 ... 3 g y 7 f x 4 ... 8 . Mutual Recursion.

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Section 4

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  1. Section 4 CSE 341 – Patrick Larson

  2. Mutual Recursion What if we need function f to call g, and function g to call f?

  3. Mutual Recursion Does this work? 1fun f x = 5 fun g y = 2 ... 6 ... 3 g y 7 f x 4... 8 ...

  4. Mutual Recursion We can employ higher order functions for a work around. fun earlier (f,x) = … f y … … fun later x = … earlier(later,y)

  5. Mutual Recursion But ML gives us special syntax for this 1fun f x = 5 and g y = 2 ... 6 ... 3 g y 7 f x 4 ... 8 ...

  6. Modules Remember that signatures are good both for organization and management and for maintaining invariants

  7. Modules - Invariants • Ordering of operations • e.g. insert, then query • Data kept in good state • e.g. fractions in lowest terms • Policies followed • e.g. don't allow shipping request without purchase order • Sensitive information hidden • e.g. force authentication for api use

  8. Currying and Higher Order Functions Questions?

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