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--- fp2023:lab08 [2023/04/25 16:29]
pdmatei
+++ fp2023:lab08 [2023/04/26 10:38] (current)
pdmatei
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 ====== Lab 08: Polymorphism =======
-===== 8.1. Ad-hoc polymorphism =====
+===== 8.1. Companion objects and Option =====
 Consider the following implementation of the type ''Nat'', which you are well-familiar with:
@@ Line 32: / Line 32: @@
 which can be called simply as: ''Nat(5)''. Also, we can ** (2) overload** ''apply'' in order to support creating naturals with the call ''Nat(.)'' from different other types.
-**8.1.** Create a companion object for ''Nat'' and add appropriate apply functions in order to make the expression ''Nat(1) + Zero + Nat("2")'' successfully compile and run.
+**8.1.1.** Create a companion object for ''Nat'' and add appropriate apply functions in order to make the expression ''Nat(1) + Zero + Nat("2")'' successfully compile and run.
+**8.1.2.** Define a function that takes a list of integers and converts them to a list of type ''List[Option[Nat]]''. If an integer ''x'' is positive, it should become a value ''Some(x)''. Otherwise it should become ''None''.
+<code scala>
+def fromList(l: List[Integer]): List[Option[Nat]] = ???
+</code>
+**8.1.3.** Define a function which takes a list of ''Option[Nat]'' and converts it to ''Option[List[Nat]]''. The logic here is that if the list contains at least one ''None'' value (hence **some** conversion from integer failed), then the result should be ''None'' . Otherwise, it should be a list containing all valid naturals:
+<code scala>
+def fromOptions(l: List[Option[Nat]]): Option[List[Nat]] = ???
+</code>
 ===== 8.2. Dictionaries =====