Merge pull request #220 from bjorn/count_predicate

Added Sequence.count(predicate)

builtin/core.wren

@@ -16,6 +16,16 @@ class Sequence {
     return result
   }
 
+  count(f) {
+    var result = 0
+    for (element in this) {
+      if (f.call(element)) {
+        result = result + 1
+      }
+    }
+    return result
+  }
+
   map(f) {
     var result = new List
     for (element in this) {

doc/site/core/list.markdown

@@ -11,11 +11,11 @@ Appends `item` to the end of the list.
 
 ### **clear**()
 
-Removes all items from the list.
+Removes all elements from the list.
 
 ### **count**
 
-The number of items in the list.
+The number of elements in the list.
 
 ### **insert**(index, item)
 

doc/site/core/sequence.markdown

@@ -34,6 +34,24 @@ Otherwise, returns `false`.
 
 Returns whether the sequence contains any element equal to the given element.
 
+### **count**
+
+The number of elements in the sequence.
+
+Unless a more efficient override is available, this will iterate over the
+sequence in order to determine how many elements it contains.
+
+### **count**(predicate)
+
+Returns the number of elements in the sequence that pass the `predicate`.
+
+Iterates over the sequence, passing each element to the function `predicate`
+and counting the number of times the returned value evaluates to `true`.
+
+    :::dart
+    [1, 2, 3].count {|n| n > 2} // 1.
+    [1, 2, 3].count {|n| n < 4} // 3.
+
 ### **join**(sep)
 
 Returns a string representation of the list. The string representations of the

src/vm/wren_core.c

@@ -62,6 +62,16 @@ static const char* libSource =
 "    return result\n"
 "  }\n"
 "\n"
+"  count(f) {\n"
+"    var result = 0\n"
+"    for (element in this) {\n"
+"      if (f.call(element)) {\n"
+"        result = result + 1\n"
+"      }\n"
+"    }\n"
+"    return result\n"
+"  }\n"
+"\n"
 "  map(f) {\n"
 "    var result = new List\n"
 "    for (element in this) {\n"

test/core/list/count_predicate.wren

@@ -0,0 +1,6 @@
+var a = [1, 2, 3]
+
+IO.print(a.count {|x| x > 3 })      // expect: 0
+IO.print(a.count {|x| x > 1 })      // expect: 2
+
+IO.print([].count {|x| true })      // expect: 0

test/core/list/count_predicate_non_bool_returning_fn.wren

@@ -0,0 +1,3 @@
+var a = [1, 2, 3]
+
+IO.print(a.count {|x| "truthy" })   // expect: 3

test/core/list/count_predicate_non_function_arg.wren

@@ -0,0 +1,3 @@
+var a = [1, 2, 3]
+
+a.count("string") // expect runtime error: String does not implement 'call(_)'.