playground: declare an eval function

Mimicking "cue eval", which is separate from exporting.
Note that its behavior is exactly the same as export for now;
the following commits will start changing the implementation and tests.

Some test cases are added to show the upcoming changes in behavior.
The "incomplete values that should perhaps be an error" test cases
now use eval rather than export, since we don't want to simply stop
with an incomplete error like "cue export" would.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I976dd4c81b812e3b14b9c1836570161fa98db13e
Dispatch-Trailer: {"type":"trybot","CL":1170942,"patchset":1,"ref":"refs/changes/42/1170942/1","targetBranch":"alpha"}

playground/impl.go

@@ -36,6 +36,7 @@ type function string
 
 const (
 	functionExport function = "export"
+	functionEval   function = "eval"
 	functionDef    function = "def"
 )
 
@@ -58,7 +59,7 @@ const (
 func handleCUECompile(in input, fn function, out output, inputVal string) (string, error) {
 	// TODO implement more functions
 	switch fn {
-	case functionExport, functionDef:
+	case functionExport, functionEval, functionDef:
 	default:
 		return "", fmt.Errorf("function %q is not implemented", fn)
 	}

playground/impl_test.go

@@ -34,16 +34,19 @@ var testTable = []struct {
 
 	// Incomplete values.
 	{inputCUE, functionDef, outputCUE, "foo: int", "foo: int\n", ""},
+	{inputCUE, functionEval, outputCUE, "foo: int", "foo: int\n", ""},
 	{inputCUE, functionExport, outputCUE, "foo: int", "foo: int\n", ""},
 	{inputCUE, functionExport, outputJSON, "foo: int", "", "foo: incomplete value int"},
 
 	// Selecting defaults; def does less.
 	{inputCUE, functionDef, outputCUE, "foo: int | *3", "foo: int | *3\n", ""},
+	{inputCUE, functionEval, outputCUE, "foo: int | *3", "foo: 3\n", ""},
 	{inputCUE, functionExport, outputCUE, "foo: int | *3", "foo: 3\n", ""},
 	{inputCUE, functionExport, outputJSON, "foo: int | *3", "{\n    \"foo\": 3\n}\n", ""},
 
 	// Simplifying values; def does less.
 	{inputCUE, functionDef, outputCUE, "foo: [1, 2, 3][1]", "foo: [1, 2, 3][1]\n", ""},
+	{inputCUE, functionEval, outputCUE, "foo: [1, 2, 3][1]", "foo: 2\n", ""},
 	{inputCUE, functionExport, outputCUE, "foo: [1, 2, 3][1]", "foo: 2\n", ""},
 	{inputCUE, functionExport, outputJSON, "foo: [1, 2, 3][1]", "{\n    \"foo\": 2\n}\n", ""},
 
@@ -69,7 +72,7 @@ var testTable = []struct {
 
 	// Cases which one could argue should be errors, beyond just being incomplete.
 	{
-		inputCUE, functionExport, outputCUE,
+		inputCUE, functionEval, outputCUE,
 		`
 			x: string
 			y: (x): string
@@ -78,7 +81,7 @@ var testTable = []struct {
 		"",
 	},
 	{
-		inputCUE, functionExport, outputCUE,
+		inputCUE, functionEval, outputCUE,
 		`
 			x: x2: "foo"
 			y: x.missing