Add some missing Dict and Set functions

Also remove some unnecessary Hash and Eq restrictions

crates/compiler/builtins/roc/Dict.roc

@@ -7,6 +7,7 @@ interface Dict
         clear,
         capacity,
         len,
+        isEmpty,
         get,
         contains,
         insert,
@@ -21,6 +22,8 @@ interface Dict
         insertAll,
         keepShared,
         removeAll,
+        map,
+        joinMap,
     ]
     imports [
         Bool.{ Bool, Eq },
@@ -139,12 +142,12 @@ empty = \{} ->
 ## Returns the max number of elements the dictionary can hold before requiring a rehash.
 ## ```
 ## foodDict =
-##           Dict.empty {}
-##           |> Dict.insert "apple" "fruit"
+##     Dict.empty {}
+##     |> Dict.insert "apple" "fruit"
 ##
 ## capacityOfDict = Dict.capacity foodDict
 ## ```
-capacity : Dict k v -> Nat | k has Hash & Eq
+capacity : Dict * * -> Nat
 capacity = \@Dict { dataIndices } ->
     cap = List.len dataIndices
 
@@ -192,10 +195,20 @@ fromList = \data ->
 ##     |> Dict.len
 ##     |> Bool.isEq 3
 ## ```
-len : Dict k v -> Nat | k has Hash & Eq
+len : Dict * * -> Nat
 len = \@Dict { size } ->
     size
 
+## Check if the dictinoary is empty.
+## ```
+## Dict.isEmpty (Dict.empty {} |> Dict.insert "key" 42)
+##
+## Dict.isEmpty (Dict.empty {})
+## ```
+isEmpty : Dict * * -> Bool
+isEmpty = \@Dict { size } ->
+    size == 0
+
 ## Clears all elements from a dictionary keeping around the allocation if it isn't huge.
 ## ```
 ## songs =
@@ -225,6 +238,28 @@ clear = \@Dict { metadata, dataIndices, data } ->
             size: 0,
         }
 
+## Convert each value in the dictionary to something new, by calling a conversion
+## function on each of them which receives both the key and the old value. Then return a
+## new dictionary containing the same keys and the converted values.
+map : Dict k a, (k, a -> b) -> Dict k b | k has Hash & Eq, b has Hash & Eq
+map = \dict, transform ->
+    init = withCapacity (capacity dict)
+
+    walk dict init \answer, k, v ->
+        insert answer k (transform k v)
+
+## Like [Dict.map], except the transformation function wraps the return value
+## in a dictionary. At the end, all the dictionaries get joined together
+## (using [Dict.insertAll]) into one dictionary.
+##
+## You may know a similar function named `concatMap` in other languages.
+joinMap : Dict a b, (a, b -> Dict x y) -> Dict x y | a has Hash & Eq, x has Hash & Eq
+joinMap = \dict, transform ->
+    init = withCapacity (capacity dict) # Might be a pessimization
+
+    walk dict init \answer, k, v ->
+        insertAll answer (transform k v)
+
 ## Iterate through the keys and values in the dictionary and call the provided
 ## function with signature `state, k, v -> state` for each value, with an
 ## initial `state` value provided for the first call.

crates/compiler/builtins/roc/List.roc

@@ -208,6 +208,9 @@ interface List
 ## * Even when copying is faster, other list operations may still be slightly slower with persistent data structures. For example, even if it were a persistent data structure, [List.map], [List.walk], and [List.keepIf] would all need to traverse every element in the list and build up the result from scratch. These operations are all
 ## * Roc's compiler optimizes many list operations into in-place mutations behind the scenes, depending on how the list is being used. For example, [List.map], [List.keepIf], and [List.set] can all be optimized to perform in-place mutations.
 ## * If possible, it is usually best for performance to use large lists in a way where the optimizer can turn them into in-place mutations. If this is not possible, a persistent data structure might be faster - but this is a rare enough scenario that it would not be good for the average Roc program's performance if this were the way [List] worked by default. Instead, you can look outside Roc's standard modules for an implementation of a persistent data structure - likely built using [List] under the hood!
+
+# separator so List.isEmpty doesn't absorb the above into its doc comment
+
 ##  Check if the list is empty.
 ## ```
 ## List.isEmpty [1, 2, 3]

crates/compiler/builtins/roc/Set.roc

@@ -7,6 +7,8 @@ interface Set
         walkUntil,
         insert,
         len,
+        isEmpty,
+        capacity,
         remove,
         contains,
         toList,
@@ -14,6 +16,8 @@ interface Set
         union,
         intersection,
         difference,
+        map,
+        joinMap,
     ]
     imports [
         List,
@@ -59,6 +63,13 @@ hashSet = \hasher, @Set inner -> Hash.hash hasher inner
 empty : {} -> Set k | k has Hash & Eq
 empty = \{} -> @Set (Dict.empty {})
 
+## Return a dictionary with space allocated for a number of entries. This
+## may provide a performance optimization if you know how many entries will be
+## inserted.
+withCapacity : Nat -> Set k | k has Hash & Eq
+withCapacity = \cap ->
+    @Set (Dict.withCapacity cap)
+
 ## Creates a new `Set` with a single value.
 ## ```
 ## singleItemSet = Set.single "Apple"
@@ -115,10 +126,32 @@ expect
 ##
 ## expect countValues == 3
 ## ```
-len : Set k -> Nat | k has Hash & Eq
+len : Set * -> Nat
 len = \@Set dict ->
     Dict.len dict
 
+## Returns the max number of elements the set can hold before requiring a rehash.
+## ```
+## foodSet =
+##     Set.empty {}
+##     |> Set.insert "apple"
+##
+## capacityOfSet = Set.capacity foodSet
+## ```
+capacity : Set * -> Nat
+capacity = \@Set dict ->
+    Dict.capacity dict
+
+## Check if the set is empty.
+## ```
+## Set.isEmpty (Set.empty {} |> Set.insert 42)
+##
+## Set.isEmpty (Set.empty {})
+## ```
+isEmpty : Set * -> Bool
+isEmpty = \@Set dict ->
+    Dict.isEmpty dict
+
 # Inserting a duplicate key has no effect on length.
 expect
     actual =
@@ -261,6 +294,28 @@ walk : Set k, state, (state, k -> state) -> state | k has Hash & Eq
 walk = \@Set dict, state, step ->
     Dict.walk dict state (\s, k, _ -> step s k)
 
+## Convert each value in the set to something new, by calling a conversion
+## function on each of them which receives the old value. Then return a
+## new set containing the converted values.
+map : Set a, (a -> b) -> Set b | a has Hash & Eq, b has Hash & Eq
+map = \set, transform ->
+    init = withCapacity (capacity set)
+
+    walk set init \answer, k ->
+        insert answer (transform k)
+
+## Like [Set.map], except the transformation function wraps the return value
+## in a set. At the end, all the sets get joined together
+## (using [Set.union]) into one set.
+##
+## You may know a similar function named `concatMap` in other languages.
+joinMap : Set a, (a -> Set b) -> Set b | a has Hash & Eq, b has Hash & Eq
+joinMap = \set, transform ->
+    init = withCapacity (capacity set) # Might be a pessimization
+
+    walk set init \answer, k ->
+        union answer (transform k)
+
 ## Iterate through the values of a given `Set` and build a value, can stop
 ## iterating part way through the collection.
 ## ```