diff --git a/config/lang/eval_test.go b/config/lang/eval_test.go
index 6af2c714b..8a3195fe1 100644
--- a/config/lang/eval_test.go
+++ b/config/lang/eval_test.go
@@ -95,6 +95,22 @@ func TestEval(t *testing.T) {
 			ast.TypeString,
 		},
 
+		{
+			"foo ${42+2*2}",
+			nil,
+			false,
+			"foo 88",
+			ast.TypeString,
+		},
+
+		{
+			"foo ${42+(2*2)}",
+			nil,
+			false,
+			"foo 46",
+			ast.TypeString,
+		},
+
 		{
 			"foo ${bar+1}",
 			&ast.BasicScope{
diff --git a/config/lang/lang.y b/config/lang/lang.y
index 9e4b9baaf..c531860e5 100644
--- a/config/lang/lang.y
+++ b/config/lang/lang.y
@@ -98,7 +98,11 @@ interpolation:
     }
 
 expr:
-    literalModeTop
+    PAREN_LEFT expr PAREN_RIGHT
+    {
+        $$ = $2
+    }
+|   literalModeTop
     {
         $$ = $1
     }
diff --git a/config/lang/y.go b/config/lang/y.go
index 75b450d25..e7dd185ae 100644
--- a/config/lang/y.go
+++ b/config/lang/y.go
@@ -50,7 +50,7 @@ const parserEofCode = 1
 const parserErrCode = 2
 const parserMaxDepth = 200
 
-//line lang.y:161
+//line lang.y:165
 
 //line yacctab:1
 var parserExca = []int{
@@ -59,51 +59,51 @@ var parserExca = []int{
 	-2, 0,
 }
 
-const parserNprod = 18
+const parserNprod = 19
 const parserPrivate = 57344
 
 var parserTokenNames []string
 var parserStates []string
 
-const parserLast = 26
+const parserLast = 30
 
 var parserAct = []int{
 
-	9, 7, 7, 15, 3, 20, 21, 8, 14, 13,
-	11, 12, 6, 6, 15, 8, 17, 19, 16, 10,
-	2, 1, 22, 18, 4, 5,
+	9, 20, 16, 16, 7, 7, 3, 18, 10, 8,
+	1, 17, 14, 12, 13, 6, 6, 19, 8, 22,
+	15, 23, 24, 11, 2, 25, 16, 21, 4, 5,
 }
 var parserPact = []int{
 
-	-2, -1000, -2, -1000, -1000, -1000, -1000, -3, -1000, 3,
-	-2, -1000, -1000, 10, -1000, -3, -3, -1000, -4, -8,
-	-1000, -3, -8,
+	1, -1000, 1, -1000, -1000, -1000, -1000, 0, -1000, 15,
+	0, 1, -1000, -1000, -1, -1000, 0, -8, 0, -1000,
+	-1000, 12, -9, -1000, 0, -9,
 }
 var parserPgo = []int{
 
-	0, 0, 25, 24, 19, 4, 23, 21,
+	0, 0, 29, 28, 23, 6, 27, 10,
 }
 var parserR1 = []int{
 
 	0, 7, 7, 4, 4, 5, 5, 2, 1, 1,
-	1, 1, 1, 1, 6, 6, 6, 3,
+	1, 1, 1, 1, 1, 6, 6, 6, 3,
 }
 var parserR2 = []int{
 
-	0, 0, 1, 1, 2, 1, 1, 3, 1, 1,
-	1, 3, 1, 4, 0, 3, 1, 1,
+	0, 0, 1, 1, 2, 1, 1, 3, 3, 1,
+	1, 1, 3, 1, 4, 0, 3, 1, 1,
 }
 var parserChk = []int{
 
 	-1000, -7, -4, -5, -3, -2, 15, 4, -5, -1,
-	-4, 13, 14, 12, 5, 11, 8, -1, -6, -1,
-	9, 10, -1,
+	8, -4, 13, 14, 12, 5, 11, -1, 8, -1,
+	9, -6, -1, 9, 10, -1,
 }
 var parserDef = []int{
 
-	1, -2, 2, 3, 5, 6, 17, 0, 4, 0,
-	8, 9, 10, 12, 7, 0, 14, 11, 0, 16,
-	13, 0, 15,
+	1, -2, 2, 3, 5, 6, 18, 0, 4, 0,
+	0, 9, 10, 11, 13, 7, 0, 0, 15, 12,
+	8, 0, 17, 14, 0, 16,
 }
 var parserTok1 = []int{
 
@@ -412,10 +412,15 @@ parserdefault:
 	case 8:
 		//line lang.y:102
 		{
-			parserVAL.node = parserS[parserpt-0].node
+			parserVAL.node = parserS[parserpt-1].node
 		}
 	case 9:
 		//line lang.y:106
+		{
+			parserVAL.node = parserS[parserpt-0].node
+		}
+	case 10:
+		//line lang.y:110
 		{
 			parserVAL.node = &ast.LiteralNode{
 				Value: parserS[parserpt-0].token.Value.(int),
@@ -423,8 +428,8 @@ parserdefault:
 				Posx:  parserS[parserpt-0].token.Pos,
 			}
 		}
-	case 10:
-		//line lang.y:114
+	case 11:
+		//line lang.y:118
 		{
 			parserVAL.node = &ast.LiteralNode{
 				Value: parserS[parserpt-0].token.Value.(float64),
@@ -432,8 +437,8 @@ parserdefault:
 				Posx:  parserS[parserpt-0].token.Pos,
 			}
 		}
-	case 11:
-		//line lang.y:122
+	case 12:
+		//line lang.y:126
 		{
 			parserVAL.node = &ast.Arithmetic{
 				Op:    parserS[parserpt-1].token.Value.(ast.ArithmeticOp),
@@ -441,33 +446,33 @@ parserdefault:
 				Posx:  parserS[parserpt-2].node.Pos(),
 			}
 		}
-	case 12:
-		//line lang.y:130
-		{
-			parserVAL.node = &ast.VariableAccess{Name: parserS[parserpt-0].token.Value.(string), Posx: parserS[parserpt-0].token.Pos}
-		}
 	case 13:
 		//line lang.y:134
 		{
-			parserVAL.node = &ast.Call{Func: parserS[parserpt-3].token.Value.(string), Args: parserS[parserpt-1].nodeList, Posx: parserS[parserpt-3].token.Pos}
+			parserVAL.node = &ast.VariableAccess{Name: parserS[parserpt-0].token.Value.(string), Posx: parserS[parserpt-0].token.Pos}
 		}
 	case 14:
-		//line lang.y:139
+		//line lang.y:138
 		{
-			parserVAL.nodeList = nil
+			parserVAL.node = &ast.Call{Func: parserS[parserpt-3].token.Value.(string), Args: parserS[parserpt-1].nodeList, Posx: parserS[parserpt-3].token.Pos}
 		}
 	case 15:
 		//line lang.y:143
 		{
-			parserVAL.nodeList = append(parserS[parserpt-2].nodeList, parserS[parserpt-0].node)
+			parserVAL.nodeList = nil
 		}
 	case 16:
 		//line lang.y:147
 		{
-			parserVAL.nodeList = append(parserVAL.nodeList, parserS[parserpt-0].node)
+			parserVAL.nodeList = append(parserS[parserpt-2].nodeList, parserS[parserpt-0].node)
 		}
 	case 17:
-		//line lang.y:153
+		//line lang.y:151
+		{
+			parserVAL.nodeList = append(parserVAL.nodeList, parserS[parserpt-0].node)
+		}
+	case 18:
+		//line lang.y:157
 		{
 			parserVAL.node = &ast.LiteralNode{
 				Value: parserS[parserpt-0].token.Value.(string),
diff --git a/config/lang/y.output b/config/lang/y.output
index 64dfe04fc..17352390d 100644
--- a/config/lang/y.output
+++ b/config/lang/y.output
@@ -51,25 +51,26 @@ state 5
 
 
 state 6
-	literal:  STRING.    (17)
+	literal:  STRING.    (18)
 
-	.  reduce 17 (src line 151)
+	.  reduce 18 (src line 155)
 
 
 state 7
 	interpolation:  PROGRAM_BRACKET_LEFT.expr PROGRAM_BRACKET_RIGHT 
 
 	PROGRAM_BRACKET_LEFT  shift 7
-	IDENTIFIER  shift 13
-	INTEGER  shift 11
-	FLOAT  shift 12
+	PAREN_LEFT  shift 10
+	IDENTIFIER  shift 14
+	INTEGER  shift 12
+	FLOAT  shift 13
 	STRING  shift 6
 	.  error
 
 	expr  goto 9
 	interpolation  goto 5
 	literal  goto 4
-	literalModeTop  goto 10
+	literalModeTop  goto 11
 	literalModeValue  goto 3
 
 state 8
@@ -82,146 +83,181 @@ state 9
 	interpolation:  PROGRAM_BRACKET_LEFT expr.PROGRAM_BRACKET_RIGHT 
 	expr:  expr.ARITH_OP expr 
 
-	PROGRAM_BRACKET_RIGHT  shift 14
-	ARITH_OP  shift 15
+	PROGRAM_BRACKET_RIGHT  shift 15
+	ARITH_OP  shift 16
 	.  error
 
 
 state 10
-	literalModeTop:  literalModeTop.literalModeValue 
-	expr:  literalModeTop.    (8)
+	expr:  PAREN_LEFT.expr PAREN_RIGHT 
 
 	PROGRAM_BRACKET_LEFT  shift 7
-	STRING  shift 6
-	.  reduce 8 (src line 100)
-
-	interpolation  goto 5
-	literal  goto 4
-	literalModeValue  goto 8
-
-state 11
-	expr:  INTEGER.    (9)
-
-	.  reduce 9 (src line 105)
-
-
-state 12
-	expr:  FLOAT.    (10)
-
-	.  reduce 10 (src line 113)
-
-
-state 13
-	expr:  IDENTIFIER.    (12)
-	expr:  IDENTIFIER.PAREN_LEFT args PAREN_RIGHT 
-
-	PAREN_LEFT  shift 16
-	.  reduce 12 (src line 129)
-
-
-state 14
-	interpolation:  PROGRAM_BRACKET_LEFT expr PROGRAM_BRACKET_RIGHT.    (7)
-
-	.  reduce 7 (src line 94)
-
-
-state 15
-	expr:  expr ARITH_OP.expr 
-
-	PROGRAM_BRACKET_LEFT  shift 7
-	IDENTIFIER  shift 13
-	INTEGER  shift 11
-	FLOAT  shift 12
+	PAREN_LEFT  shift 10
+	IDENTIFIER  shift 14
+	INTEGER  shift 12
+	FLOAT  shift 13
 	STRING  shift 6
 	.  error
 
 	expr  goto 17
 	interpolation  goto 5
 	literal  goto 4
-	literalModeTop  goto 10
+	literalModeTop  goto 11
 	literalModeValue  goto 3
 
-state 16
-	expr:  IDENTIFIER PAREN_LEFT.args PAREN_RIGHT 
-	args: .    (14)
+state 11
+	literalModeTop:  literalModeTop.literalModeValue 
+	expr:  literalModeTop.    (9)
 
 	PROGRAM_BRACKET_LEFT  shift 7
-	IDENTIFIER  shift 13
-	INTEGER  shift 11
-	FLOAT  shift 12
 	STRING  shift 6
-	.  reduce 14 (src line 138)
+	.  reduce 9 (src line 105)
+
+	interpolation  goto 5
+	literal  goto 4
+	literalModeValue  goto 8
+
+state 12
+	expr:  INTEGER.    (10)
+
+	.  reduce 10 (src line 109)
+
+
+state 13
+	expr:  FLOAT.    (11)
+
+	.  reduce 11 (src line 117)
+
+
+state 14
+	expr:  IDENTIFIER.    (13)
+	expr:  IDENTIFIER.PAREN_LEFT args PAREN_RIGHT 
+
+	PAREN_LEFT  shift 18
+	.  reduce 13 (src line 133)
+
+
+state 15
+	interpolation:  PROGRAM_BRACKET_LEFT expr PROGRAM_BRACKET_RIGHT.    (7)
+
+	.  reduce 7 (src line 94)
+
+
+state 16
+	expr:  expr ARITH_OP.expr 
+
+	PROGRAM_BRACKET_LEFT  shift 7
+	PAREN_LEFT  shift 10
+	IDENTIFIER  shift 14
+	INTEGER  shift 12
+	FLOAT  shift 13
+	STRING  shift 6
+	.  error
 
 	expr  goto 19
 	interpolation  goto 5
 	literal  goto 4
-	literalModeTop  goto 10
+	literalModeTop  goto 11
 	literalModeValue  goto 3
-	args  goto 18
 
 state 17
+	expr:  PAREN_LEFT expr.PAREN_RIGHT 
 	expr:  expr.ARITH_OP expr 
-	expr:  expr ARITH_OP expr.    (11)
 
-	.  reduce 11 (src line 121)
+	PAREN_RIGHT  shift 20
+	ARITH_OP  shift 16
+	.  error
 
 
 state 18
-	expr:  IDENTIFIER PAREN_LEFT args.PAREN_RIGHT 
-	args:  args.COMMA expr 
-
-	PAREN_RIGHT  shift 20
-	COMMA  shift 21
-	.  error
-
-
-state 19
-	expr:  expr.ARITH_OP expr 
-	args:  expr.    (16)
-
-	ARITH_OP  shift 15
-	.  reduce 16 (src line 146)
-
-
-state 20
-	expr:  IDENTIFIER PAREN_LEFT args PAREN_RIGHT.    (13)
-
-	.  reduce 13 (src line 133)
-
-
-state 21
-	args:  args COMMA.expr 
+	expr:  IDENTIFIER PAREN_LEFT.args PAREN_RIGHT 
+	args: .    (15)
 
 	PROGRAM_BRACKET_LEFT  shift 7
-	IDENTIFIER  shift 13
-	INTEGER  shift 11
-	FLOAT  shift 12
+	PAREN_LEFT  shift 10
+	IDENTIFIER  shift 14
+	INTEGER  shift 12
+	FLOAT  shift 13
 	STRING  shift 6
-	.  error
+	.  reduce 15 (src line 142)
 
 	expr  goto 22
 	interpolation  goto 5
 	literal  goto 4
-	literalModeTop  goto 10
+	literalModeTop  goto 11
 	literalModeValue  goto 3
+	args  goto 21
+
+state 19
+	expr:  expr.ARITH_OP expr 
+	expr:  expr ARITH_OP expr.    (12)
+
+	.  reduce 12 (src line 125)
+
+
+state 20
+	expr:  PAREN_LEFT expr PAREN_RIGHT.    (8)
+
+	.  reduce 8 (src line 100)
+
+
+state 21
+	expr:  IDENTIFIER PAREN_LEFT args.PAREN_RIGHT 
+	args:  args.COMMA expr 
+
+	PAREN_RIGHT  shift 23
+	COMMA  shift 24
+	.  error
+
 
 state 22
 	expr:  expr.ARITH_OP expr 
-	args:  args COMMA expr.    (15)
+	args:  expr.    (17)
 
-	ARITH_OP  shift 15
-	.  reduce 15 (src line 142)
+	ARITH_OP  shift 16
+	.  reduce 17 (src line 150)
+
+
+state 23
+	expr:  IDENTIFIER PAREN_LEFT args PAREN_RIGHT.    (14)
+
+	.  reduce 14 (src line 137)
+
+
+state 24
+	args:  args COMMA.expr 
+
+	PROGRAM_BRACKET_LEFT  shift 7
+	PAREN_LEFT  shift 10
+	IDENTIFIER  shift 14
+	INTEGER  shift 12
+	FLOAT  shift 13
+	STRING  shift 6
+	.  error
+
+	expr  goto 25
+	interpolation  goto 5
+	literal  goto 4
+	literalModeTop  goto 11
+	literalModeValue  goto 3
+
+state 25
+	expr:  expr.ARITH_OP expr 
+	args:  args COMMA expr.    (16)
+
+	ARITH_OP  shift 16
+	.  reduce 16 (src line 146)
 
 
 15 terminals, 8 nonterminals
-18 grammar rules, 23/2000 states
+19 grammar rules, 26/2000 states
 0 shift/reduce, 0 reduce/reduce conflicts reported
 57 working sets used
-memory: parser 30/30000
-18 extra closures
-33 shift entries, 1 exceptions
-13 goto entries
-19 entries saved by goto default
-Optimizer space used: output 26/30000
-26 table entries, 0 zero
-maximum spread: 15, maximum offset: 21
+memory: parser 35/30000
+21 extra closures
+45 shift entries, 1 exceptions
+14 goto entries
+23 entries saved by goto default
+Optimizer space used: output 30/30000
+30 table entries, 0 zero
+maximum spread: 15, maximum offset: 24