Stdlib: filter_map function for Set

changelog/2463

+
+author: er433
+description: "\\nNew function in module `Set`: `val filter_map : ('a -> b option) -> 'a set -> 'b set`.\\n\\n"
+merge_request: '2463'
+title: "Stdlib: filter_map function for Set"
+type: added
+            
\ No newline at end of file

gitlab-pages/docs/reference/set.md

@@ -425,3 +425,16 @@ let sum_of_elements_desc : int = Set.fold_desc (sum_right, my_set, 0);
 ```
 
 </Syntax>
+
+
+<SyntaxTitle syntax="cameligo">
+val filter_map : ('a -> 'b option) -> 'a set -> 'b set
+</SyntaxTitle>
+
+<SyntaxTitle syntax="jsligo">
+let filter_map: (mapper: ((item: 'a) => option&lt;'b&gt;), set: set&lt;'a&gt;) => set&lt;'b&gt;
+</SyntaxTitle>
+
+Apply a function to items of a set to create a new set, but the function can omit certain elements by returning `None`.
+
+Notice: built in terms of `fold_desc`.

src/main/build/ligo_lib/std_lib.mligo

@@ -132,6 +132,8 @@ module Set = struct
   let iter (type a) (f : a -> unit) (s : a set) : unit = [%external ("SET_ITER", f, s)]
   let fold (type a b) (f : b * a -> b) (s : a set) (i : b) : b = [%external ("SET_FOLD", f, s, i)]
   let fold_desc (type a b) (f : a * b -> b) (s : a set) (i : b) : b = [%external ("SET_FOLD_DESC", f, s, i)]
+  let filter_map (type a b) (f : a -> b option) (xs : a set) : b set =
+    fold_desc (fun (a : a * b set) -> match f a.0 with | None -> a.1 | Some b -> add b a.1) xs (empty : b set)
 end
 
 module List = struct
@@ -149,7 +151,7 @@ module List = struct
   let find_opt (type a) (f : a -> bool) (xs : a list) : a option = 
     fold_right (fun (a : a * a option) -> if f a.0 then Some a.0 else a.1) xs None
   let filter_map (type a b) (f : a -> b option) (xs : a list) : b list =
-    fold_right (fun (a : a * b list) -> match f a.0 with | None -> a.1 | Some b -> (b :: a . 1)) xs []
+    fold_right (fun (a : a * b list) -> match f a.0 with | None -> a.1 | Some b -> (b :: a.1)) xs []
   let update (type a) (f : a -> a option) (xs : a list) : a list =
     map (fun a -> match f a with | None -> a | Some a -> a) xs
   let update_with (type a) (f : a -> bool) (v : a) (xs : a list) : a list =

src/test/contracts/set_arithmetic.jsligo

@@ -35,4 +35,6 @@ let aggregate = ( [i,j] : [list <int>, int]) : list <int> => list ([j, ...i]);
 let fold_op  = (s : set <int>) : list<int> => Set.fold (aggregate, s, list([]) as list<int>)
 
 let aggregate2 = ( [i,j] : [int , list<int>]) : list<int> => list ([i, ...j]);
-let fold_right = (s : set <int>) : list<int> => Set.fold_desc (aggregate2, s, list([]) as list<int>)
\ No newline at end of file
+let fold_right = (s : set <int>) : list<int> => Set.fold_desc (aggregate2, s, list([]) as list<int>);
+
+let filter_map_lit = Set.filter_map((s : string) => { if (String.length(s) > (3 as nat)) { return Some(String.length(s)); } ; return None(); } , literal_op());