adds functions for checking the type of variables

lang/funcs/type.go

@@ -0,0 +1,69 @@
+package funcs
+
+import (
+	"github.com/zclconf/go-cty/cty"
+	"github.com/zclconf/go-cty/cty/function"
+)
+
+var TypeFunc = function.New(&function.Spec{
+	Params: []function.Parameter{
+		{
+			Name:      "variable",
+			Type:      cty.DynamicPseudoType,
+			AllowNull: true,
+		},
+	},
+	Type: function.StaticReturnType(cty.String),
+	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
+		varType := getType(args[0])
+		return cty.StringVal(varType), nil
+	},
+})
+
+// MakeIsTypeFunc constructs a "is..." function, like "isstring", which checks
+// the type of a given variable is of the expected type.
+// The given string checkType can be any type supported by the cty package
+func MakeIsTypeFunc(checkType string) function.Function {
+	return function.New(&function.Spec{
+		Params: []function.Parameter{
+			{
+				Name:      "variable",
+				Type:      cty.DynamicPseudoType,
+				AllowNull: true,
+			},
+		},
+		Type: function.StaticReturnType(cty.Bool),
+		Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
+			checked := getType(args[0]) == checkType
+			return cty.BoolVal(checked), nil
+		},
+	})
+}
+
+func getType(arg cty.Value) string {
+	var varType string
+
+	// We have some special cases here, because var.Type().FriendlyName() does
+	// not always give what we want.
+	// In case the input var is null, it returns "any value"
+	// For collection types it returns "list/map/set of strings" etc
+	// We only want "list/map/set" instead.
+	if arg.IsNull() {
+		varType = "null"
+	} else if arg.Type().IsListType() {
+		varType = "list"
+	} else if arg.Type().IsMapType() {
+		varType = "map"
+	} else if arg.Type().IsSetType() {
+		varType = "set"
+	} else {
+		varType = arg.Type().FriendlyName()
+	}
+
+	return varType
+}
+
+// Type returns the type of a given var as string
+func Type(t cty.Value) (cty.Value, error) {
+	return TypeFunc.Call([]cty.Value{t})
+}

lang/funcs/type_test.go

@@ -0,0 +1,113 @@
+package funcs
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/zclconf/go-cty/cty"
+)
+
+func TestType(t *testing.T) {
+	tests := []struct {
+		Value cty.Value
+		Want  string
+	}{
+		{
+			cty.BoolVal(true),
+			"bool",
+		},
+		{
+			cty.ListVal([]cty.Value{
+				cty.StringVal("foo"),
+				cty.StringVal("bar"),
+			}),
+			"list",
+		},
+		{
+			cty.MapVal(map[string]cty.Value{
+				"foo": cty.StringVal("foo"),
+				"bar": cty.StringVal("bar")}),
+			"map",
+		},
+		{
+			cty.NilVal,
+			"null",
+		},
+		{
+			cty.NumberIntVal(42),
+			"number",
+		},
+		{
+			cty.ObjectVal(map[string]cty.Value{
+				"foo": cty.StringVal("foo"),
+				"bar": cty.StringVal("bar")}),
+			"object",
+		},
+		{
+			cty.SetVal([]cty.Value{
+				cty.StringVal("foo"),
+				cty.StringVal("bar"),
+			}),
+			"set",
+		},
+		{
+			cty.StringVal("foo"),
+			"string",
+		},
+		{
+			cty.TupleVal([]cty.Value{
+				cty.StringVal("foo"),
+				cty.StringVal("bar"),
+			}),
+			"tuple",
+		},
+	}
+
+	// prevValue is used to test negative results, to ensure the is* functions
+	// do not just always return true
+	prevValue := cty.NumberIntVal(42)
+
+	for _, test := range tests {
+
+		t.Run(fmt.Sprintf("type(%#v)", test.Value), func(t *testing.T) {
+			got, err := Type(test.Value)
+
+			if err != nil {
+				t.Fatalf("unexpected error: %s", err)
+			}
+
+			if got.AsString() != test.Want {
+				t.Errorf("wrong result\ngot:  %#v\nwant: %#v", got, test.Want)
+			}
+		})
+
+		t.Run(fmt.Sprintf("is%s()", test.Want), func(t *testing.T) {
+			f := MakeIsTypeFunc(test.Want)
+
+			//testing for positive results
+			got, err := f.Call([]cty.Value{test.Value})
+
+			if err != nil {
+				t.Fatalf("unexpected error: %s", err)
+			}
+
+			if got.False() {
+				t.Error("wrong result\ngot:  false\nwant: true")
+			}
+
+			// testing for negative results
+			got, err = f.Call([]cty.Value{prevValue})
+
+			if err != nil {
+				t.Fatalf("unexpected error: %s", err)
+			}
+
+			if got.True() {
+				t.Error("wrong result\ngot:  true\nwant: false")
+			}
+
+			// preparing prevValue for next test iteration
+			prevValue = test.Value
+		})
+	}
+}

lang/functions.go

@@ -72,6 +72,15 @@ func (s *Scope) Functions() map[string]function.Function {
 			"formatlist":       stdlib.FormatListFunc,
 			"indent":           funcs.IndentFunc,
 			"index":            funcs.IndexFunc,
+			"isbool":           funcs.MakeIsTypeFunc("bool"),
+			"islist":           funcs.MakeIsTypeFunc("list"),
+			"ismap":            funcs.MakeIsTypeFunc("map"),
+			"isnull":           funcs.MakeIsTypeFunc("null"),
+			"isnumber":         funcs.MakeIsTypeFunc("number"),
+			"isobject":         funcs.MakeIsTypeFunc("object"),
+			"isset":            funcs.MakeIsTypeFunc("set"),
+			"isstring":         funcs.MakeIsTypeFunc("string"),
+			"istuple":          funcs.MakeIsTypeFunc("tuple"),
 			"join":             funcs.JoinFunc,
 			"jsondecode":       stdlib.JSONDecodeFunc,
 			"jsonencode":       stdlib.JSONEncodeFunc,
@@ -119,6 +128,7 @@ func (s *Scope) Functions() map[string]function.Function {
 			"tomap":            funcs.MakeToFunc(cty.Map(cty.DynamicPseudoType)),
 			"transpose":        funcs.TransposeFunc,
 			"trimspace":        funcs.TrimSpaceFunc,
+			"type":             funcs.TypeFunc,
 			"upper":            stdlib.UpperFunc,
 			"urlencode":        funcs.URLEncodeFunc,
 			"uuid":             funcs.UUIDFunc,