Add filter expression function

cmd/docgen/docs/base_test.go

@@ -43,7 +43,7 @@ func TestGenerateDocs(t *testing.T) {
 	context := completion["context"].(map[string]interface{})
 	functions := completion["functions"].([]interface{})
 
-	assert.Equal(t, 87, len(functions))
+	assert.Equal(t, 88, len(functions))
 
 	types := context["types"].([]interface{})
 	assert.Equal(t, 18, len(types))

excellent/functions/builtin.go

@@ -109,6 +109,7 @@ func init() {
 		"sum":      OneArrayFunction(Sum),
 		"unique":   OneArrayFunction(Unique),
 		"concat":   TwoArrayFunction(Concat),
+		"filter":   TwoArgFunction(Filter),
 
 		// encoded text functions
 		"urn_parts":        OneTextFunction(URNParts),
@@ -1689,6 +1690,39 @@ func Concat(env envs.Environment, array1 *types.XArray, array2 *types.XArray) ty
 	return types.NewXArray(both...)
 }
 
+// Filter returns a new array with the items from `array` that when passed to `func` return true.
+//
+//	@(filter(array(1, 0, 2), boolean)) -> [1, 2]
+//	@(filter(array("a", "b", "c"), (x) => x != "c")) -> [a, b]
+//
+// @function filter(array, func)
+func Filter(env envs.Environment, arg1 types.XValue, arg2 types.XValue) types.XValue {
+	array, xerr := types.ToXArray(env, arg1)
+	if xerr != nil {
+		return xerr
+	}
+	function, xerr := types.ToXFunction(arg2)
+	if xerr != nil {
+		return xerr
+	}
+
+	result := make([]types.XValue, 0, array.Count())
+
+	for i := 0; i < array.Count(); i++ {
+		item := array.Get(i)
+		keep := function.Call(env, []types.XValue{item})
+		asBool, xerr := types.ToXBoolean(keep)
+		if xerr != nil {
+			return xerr
+		}
+		if asBool.Native() {
+			result = append(result, item)
+		}
+	}
+
+	return types.NewXArray(result...)
+}
+
 //------------------------------------------------------------------------------------------
 // Encoded Text Functions
 //------------------------------------------------------------------------------------------
@@ -2174,14 +2208,12 @@ func ForEach(env envs.Environment, args ...types.XValue) types.XValue {
 	if xerr != nil {
 		return xerr
 	}
-
-	function, isFunction := args[1].(*types.XFunction)
-	if !isFunction {
-		return types.NewXErrorf("requires an function as its second argument")
+	function, xerr := types.ToXFunction(args[1])
+	if xerr != nil {
+		return xerr
 	}
 
 	otherArgs := args[2:]
-
 	result := make([]types.XValue, array.Count())
 
 	for i := 0; i < array.Count(); i++ {
@@ -2211,14 +2243,12 @@ func ForEachValue(env envs.Environment, args ...types.XValue) types.XValue {
 	if xerr != nil {
 		return xerr
 	}
-
-	function, isFunction := args[1].(*types.XFunction)
-	if !isFunction {
-		return types.NewXErrorf("requires an function as its second argument")
+	function, xerr := types.ToXFunction(args[1])
+	if xerr != nil {
+		return xerr
 	}
 
 	otherArgs := args[2:]
-
 	props := object.Properties()
 	result := make(map[string]types.XValue, len(props))
 

excellent/functions/builtin_test.go

@@ -269,6 +269,10 @@ func TestFunctions(t *testing.T) {
 		{"field", dmy, []types.XValue{xs("hello"), xs("1"), ERROR}, ERROR},
 		{"field", dmy, []types.XValue{}, ERROR},
 
+		{"filter", dmy, []types.XValue{xa(xi(1), xi(0), xi(2)), xf("boolean")}, xa(xi(1), xi(2))},
+		{"filter", dmy, []types.XValue{ERROR, xf("boolean")}, ERROR},
+		{"filter", dmy, []types.XValue{xa(xi(1), xi(0), xi(2)), ERROR}, ERROR},
+
 		{"foreach", dmy, []types.XValue{xa(xs("a"), xs("b"), xs("c")), xf("upper")}, xa(xs("A"), xs("B"), xs("C"))},
 		{"foreach", dmy, []types.XValue{xa(xs("the man"), xs("fox"), xs("jumped up")), xf("word"), xi(0)}, xa(xs("the"), xs("fox"), xs("jumped"))},
 		{"foreach", dmy, []types.XValue{ERROR, xf("upper")}, ERROR},

excellent/types/function.go

@@ -82,3 +82,12 @@ func (x *XFunction) Equals(o XValue) bool {
 }
 
 var _ XValue = (*XFunction)(nil)
+
+// ToXFunction converts the given value to a function returns an error if that isn't possible
+func ToXFunction(x XValue) (*XFunction, XError) {
+	function, isFunction := x.(*XFunction)
+	if !isFunction {
+		return nil, NewXErrorf("%s is not a function", Describe(x))
+	}
+	return function, nil
+}

excellent/types/function_test.go

@@ -47,3 +47,32 @@ func TestXFunction(t *testing.T) {
 	assert.False(t, types.Equals(anon1, anon1))
 	assert.False(t, types.Equals(anon1, anon2))
 }
+
+func TestToXFunction(t *testing.T) {
+	foo := types.NewXFunction("foo", func(env envs.Environment, args ...types.XValue) types.XValue { return types.NewXText("foo") })
+	anon := types.NewXFunction("", func(env envs.Environment, args ...types.XValue) types.XValue { return types.NewXText("bar") })
+
+	types.ToXFunction(types.NewXText("hello"))
+
+	var tests = []struct {
+		value    types.XValue
+		asFunc   *types.XFunction
+		hasError bool
+	}{
+		{nil, nil, true},
+		{types.NewXText("hi"), nil, true},
+		{foo, foo, false},
+		{anon, anon, false},
+	}
+
+	for _, test := range tests {
+		fun, err := types.ToXFunction(test.value)
+
+		if test.hasError {
+			assert.Error(t, err, "expected error for input %T{%s}", test.value, test.value)
+		} else {
+			assert.NoError(t, err, "unexpected error for input %T{%s}", test.value, test.value)
+			assert.Equal(t, test.asFunc, fun, "array mismatch for input %T{%s}", test.value, test.value)
+		}
+	}
+}