feat: implement std.avg (#700)

* feat: implement std.avg

Author: deepgoel17

builtins.go

@@ -2066,6 +2066,30 @@ func builtinSum(i *interpreter, arrv value) (value, error) {
 	return makeValueNumber(sum), nil
 }
 
+func builtinAvg(i *interpreter, arrv value) (value, error) {
+	arr, err := i.getArray(arrv)
+	if err != nil {
+		return nil, err
+	}
+	
+	len := float64(arr.length())
+	if len == 0 {
+		return nil, i.Error("Cannot calculate average of an empty array.")
+	}
+	
+	sumValue, err := builtinSum(i, arrv)
+	if err != nil {
+		return nil, err
+	}
+	sum, err := i.getNumber(sumValue)
+	if err != nil {
+		return nil, err
+	}
+
+	avg := sum.value/len
+	return makeValueNumber(avg), nil
+}
+
 func builtinContains(i *interpreter, arrv value, ev value) (value, error) {
 	arr, err := i.getArray(arrv)
 	if err != nil {
@@ -2478,6 +2502,7 @@ var funcBuiltins = buildBuiltinMap([]builtin{
 	&generalBuiltin{name: "maxArray", function: builtinMaxArray, params: []generalBuiltinParameter{{name: "arr"}, {name: "keyF", defaultValue: functionID}}},
 	&unaryBuiltin{name: "native", function: builtinNative, params: ast.Identifiers{"x"}},
 	&unaryBuiltin{name: "sum", function: builtinSum, params: ast.Identifiers{"arr"}},
+	&unaryBuiltin{name: "avg", function: builtinAvg, params: ast.Identifiers{"arr"}},
 	&binaryBuiltin{name: "contains", function: builtinContains, params: ast.Identifiers{"arr", "elem"}},
 
 	// internal

linter/internal/types/stdlib.go

@@ -145,11 +145,11 @@ func prepareStdlib(g *typeGraph) {
 		"minArray":      g.newFuncType(anyArrayType, []ast.Parameter{required("arr"), optional("keyF")}),
 		"maxArray":      g.newFuncType(anyArrayType, []ast.Parameter{required("arr"), optional("keyF")}),
 		"contains":      g.newSimpleFuncType(boolType, "arr", "elem"),
-		// TODO these need test cases written by someone who understands how to make them
-		"all":      g.newSimpleFuncType(boolArrayType, "arr"),
-		"any":      g.newSimpleFuncType(boolArrayType, "arr"),
-		"remove":   g.newSimpleFuncType(anyArrayType, "arr", "elem"),
-		"removeAt": g.newSimpleFuncType(anyArrayType, "arr", "i"),
+		"avg":		    	 g.newSimpleFuncType(numberType, "arr"),	
+		"all":           g.newSimpleFuncType(boolArrayType, "arr"),
+		"any":           g.newSimpleFuncType(boolArrayType, "arr"),
+		"remove":        g.newSimpleFuncType(anyArrayType, "arr", "elem"),
+		"removeAt":      g.newSimpleFuncType(anyArrayType, "arr", "i"),
 
 		// Sets
 

testdata/builtinAvg.golden

@@ -0,0 +1 @@
+2

testdata/builtinAvg.jsonnet

@@ -0,0 +1 @@
+std.avg([1,2,3])