proc: add min and max builtins

pkg/proc/eval.go

@@ -1498,6 +1498,8 @@ var supportedBuiltins = map[string]func([]*Variable, []ast.Expr) (*Variable, err
 	"complex": complexBuiltin,
 	"imag":    imagBuiltin,
 	"real":    realBuiltin,
+	"min":     minBuiltin,
+	"max":     maxBuiltin,
 }
 
 func capBuiltin(args []*Variable, nodeargs []ast.Expr) (*Variable, error) {
@@ -1662,6 +1664,57 @@ func realBuiltin(args []*Variable, nodeargs []ast.Expr) (*Variable, error) {
 	return newConstant(constant.Real(arg.Value), arg.mem), nil
 }
 
+func minBuiltin(args []*Variable, nodeargs []ast.Expr) (*Variable, error) {
+	return minmaxBuiltin("min", token.LSS, args, nodeargs)
+}
+
+func maxBuiltin(args []*Variable, nodeargs []ast.Expr) (*Variable, error) {
+	return minmaxBuiltin("max", token.GTR, args, nodeargs)
+}
+
+func minmaxBuiltin(name string, op token.Token, args []*Variable, nodeargs []ast.Expr) (*Variable, error) {
+	var best *Variable
+
+	for i := range args {
+		if args[i].Kind == reflect.String {
+			args[i].loadValue(loadFullValueLongerStrings)
+		} else {
+			args[i].loadValue(loadFullValue)
+		}
+
+		if args[i].Unreadable != nil {
+			return nil, fmt.Errorf("could not load %q: %v", exprToString(nodeargs[i]), args[i].Unreadable)
+		}
+		if args[i].FloatSpecial != 0 {
+			return nil, errOperationOnSpecialFloat
+		}
+
+		if best == nil {
+			best = args[i]
+			continue
+		}
+
+		_, err := negotiateType(op, args[i], best)
+		if err != nil {
+			return nil, err
+		}
+
+		v, err := compareOp(op, args[i], best)
+		if err != nil {
+			return nil, err
+		}
+
+		if v {
+			best = args[i]
+		}
+	}
+
+	if best == nil {
+		return nil, fmt.Errorf("not enough arguments to %s", name)
+	}
+	return best, nil
+}
+
 // Evaluates expressions <subexpr>.<field name> where subexpr is not a package name
 func (scope *EvalScope) evalStructSelector(op *evalop.Select, stack *evalStack) {
 	xv := stack.pop()

pkg/proc/variables_test.go

@@ -681,6 +681,13 @@ func getEvalExpressionTestCases() []varTest {
 		{"real(cpx1)", false, "1", "1", "", nil},
 		{"imag(3i)", false, "3", "3", "", nil},
 		{"real(4)", false, "4", "4", "", nil},
+		{"max(1, 2, 3)", false, "3", "3", "", nil},
+		{`max("one", "two", "three")`, false, `"two"`, `"two"`, "", nil},
+		{`min("one", "two", "three")`, false, `"one"`, `"one"`, "", nil},
+		{"max(s1[0], s1[1], s1[2])", false, `"two"`, `"two"`, "string", nil},
+		{"min(s1[0], s1[1], s1[2])", false, `"one"`, `"one"`, "string", nil},
+		{`max(s1[0], "two", s1[2])`, false, `"two"`, `"two"`, "", nil},
+		{`min(s1[0], "two", s1[2])`, false, `"one"`, `"one"`, "string", nil},
 
 		// nil
 		{"nil", false, "nil", "nil", "", nil},