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This section explores the concept of mutual recursion, where two functions call each other. It explains how mutual recursion can be implemented and offers alternatives through higher-order functions. Additionally, it touches on the importance of modules and invariants in program organization, ensuring operations are performed in a specific order and sensitive information is managed properly. The significance of signatures for clarity and maintenance in functional programming practice is also highlighted, with examples provided for better comprehension.
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Section 4 CSE 341 – Patrick Larson
Mutual Recursion What if we need function f to call g, and function g to call f?
Mutual Recursion Does this work? 1fun f x = 5 fun g y = 2 ... 6 ... 3 g y 7 f x 4... 8 ...
Mutual Recursion We can employ higher order functions for a work around. fun earlier (f,x) = … f y … … fun later x = … earlier(later,y)
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 ...
Modules Remember that signatures are good both for organization and management and for maintaining invariants
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
Currying and Higher Order Functions Questions?
