diff --git a/README.md b/README.md
index e0c6c5e..a8c53f3 100644
--- a/README.md
+++ b/README.md
@@ -31,9 +31,9 @@ Minimal complete flow implementation:
 - [x] verify proofs with BN128 pairing
 
 Improvements from the minimal implementation:
+- [x] allow to call functions in circuits language
 - [ ] allow `import` in circuits language
 - [ ] allow `for` in circuits language
-- [ ] code to flat code (improve circuit compiler)
 - [ ] move witness values calculation outside the setup phase
 - [ ] Groth16
 - [ ] multiple optimizations
@@ -54,9 +54,13 @@ In this example we will follow the equation example from [Vitalik](https://mediu
 #### Compile circuit
 Having a circuit file `test.circuit`:
 ```
-func test(private s0, public s1):
-	s2 = s0 * s0
-	s3 = s2 * s0
+func exp3(private a):
+	b = a * a
+	c = a * b
+	return c
+
+func main(private s0, public s1):
+	s3 = exp3(s0)
 	s4 = s3 + s0
 	s5 = s4 + 5
 	equals(s1, s5)
@@ -112,9 +116,13 @@ Example:
 ```go
 // compile circuit and get the R1CS
 flatCode := `
-func test(private s0, public s1):
-	s2 = s0 * s0
-	s3 = s2 * s0
+func exp3(private a):
+	b = a * a
+	c = a * b
+	return c
+
+func main(private s0, public s1):
+	s3 = exp3(s0)
 	s4 = s3 + s0
 	s5 = s4 + 5
 	equals(s1, s5)
@@ -147,8 +155,8 @@ a, b, c := circuit.GenerateR1CS()
 
 /*
 now we have the R1CS from the circuit:
-a: [[0 0 1 0 0 0 0 0] [0 0 0 1 0 0 0 0] [0 0 1 0 1 0 0 0] [5 0 0 0 0 1 0 0] [0 0 0 0 0 0 1 0] [0 1 0 0 0 0 0 0] [1 0 0 0 0 0 0 0]]
-b: [[0 0 1 0 0 0 0 0] [0 0 1 0 0 0 0 0] [1 0 0 0 0 0 0 0] [1 0 0 0 0 0 0 0] [1 0 0 0 0 0 0 0] [1 0 0 0 0 0 0 0] [1 0 0 0 0 0 0 0]]
+a: [[0 0 1 0 0 0 0 0] [0 0 1 0 0 0 0 0] [0 0 1 0 1 0 0 0] [5 0 0 0 0 1 0 0] [0 0 0 0 0 0 1 0] [0 1 0 0 0 0 0 0] [1 0 0 0 0 0 0 0]]
+b: [[0 0 1 0 0 0 0 0] [0 0 0 1 0 0 0 0] [1 0 0 0 0 0 0 0] [1 0 0 0 0 0 0 0] [1 0 0 0 0 0 0 0] [1 0 0 0 0 0 0 0] [1 0 0 0 0 0 0 0]]
 c: [[0 0 0 1 0 0 0 0] [0 0 0 0 1 0 0 0] [0 0 0 0 0 1 0 0] [0 0 0 0 0 0 1 0] [0 1 0 0 0 0 0 0] [0 0 0 0 0 0 1 0] [0 0 0 0 0 0 0 1]]
 */
 
diff --git a/circuitcompiler/circuit_test.go b/circuitcompiler/circuit_test.go
index 485406b..dcf6dab 100644
--- a/circuitcompiler/circuit_test.go
+++ b/circuitcompiler/circuit_test.go
@@ -11,7 +11,7 @@ import (
 func TestCircuitParser(t *testing.T) {
 	// y = x^3 + x + 5
 	flat := `
-	func test(private s0, public s1):
+	func main(private s0, public s1):
 		s2 = s0 * s0
 		s3 = s2 * s0
 		s4 = s3 + s0
@@ -86,3 +86,89 @@ func TestCircuitParser(t *testing.T) {
 	assert.Equal(t, len(circuit.PublicInputs), 1)
 	assert.Equal(t, len(circuit.PrivateInputs), 1)
 }
+
+func TestCircuitWithFuncCallsParser(t *testing.T) {
+	// y = x^3 + x + 5
+	code := `
+		func exp3(private a):
+			b = a * a
+			c = a * b
+			return c
+		func sum(private a, private b):
+			c = a + b
+			return c
+
+		func main(private s0, public s1):
+			s3 = exp3(s0)
+			s4 = sum(s3, s0)
+			s5 = s4 + 5
+			equals(s1, s5)
+			out = 1 * 1
+	`
+	parser := NewParser(strings.NewReader(code))
+	circuit, err := parser.Parse()
+	assert.Nil(t, err)
+
+	// flat code to R1CS
+	a, b, c := circuit.GenerateR1CS()
+	assert.Equal(t, "s0", circuit.PrivateInputs[0])
+	assert.Equal(t, "s1", circuit.PublicInputs[0])
+
+	assert.Equal(t, []string{"one", "s1", "s0", "b0", "s3", "s4", "s5", "out"}, circuit.Signals)
+
+	// expected result
+	b0 := big.NewInt(int64(0))
+	b1 := big.NewInt(int64(1))
+	b5 := big.NewInt(int64(5))
+	aExpected := [][]*big.Int{
+		[]*big.Int{b0, b0, b1, b0, b0, b0, b0, b0},
+		[]*big.Int{b0, b0, b1, b0, b0, b0, b0, b0},
+		[]*big.Int{b0, b0, b1, b0, b1, b0, b0, b0},
+		[]*big.Int{b5, b0, b0, b0, b0, b1, b0, b0},
+		[]*big.Int{b0, b0, b0, b0, b0, b0, b1, b0},
+		[]*big.Int{b0, b1, b0, b0, b0, b0, b0, b0},
+		[]*big.Int{b1, b0, b0, b0, b0, b0, b0, b0},
+	}
+	bExpected := [][]*big.Int{
+		[]*big.Int{b0, b0, b1, b0, b0, b0, b0, b0},
+		[]*big.Int{b0, b0, b0, b1, b0, b0, b0, b0},
+		[]*big.Int{b1, b0, b0, b0, b0, b0, b0, b0},
+		[]*big.Int{b1, b0, b0, b0, b0, b0, b0, b0},
+		[]*big.Int{b1, b0, b0, b0, b0, b0, b0, b0},
+		[]*big.Int{b1, b0, b0, b0, b0, b0, b0, b0},
+		[]*big.Int{b1, b0, b0, b0, b0, b0, b0, b0},
+	}
+	cExpected := [][]*big.Int{
+		[]*big.Int{b0, b0, b0, b1, b0, b0, b0, b0},
+		[]*big.Int{b0, b0, b0, b0, b1, b0, b0, b0},
+		[]*big.Int{b0, b0, b0, b0, b0, b1, b0, b0},
+		[]*big.Int{b0, b0, b0, b0, b0, b0, b1, b0},
+		[]*big.Int{b0, b1, b0, b0, b0, b0, b0, b0},
+		[]*big.Int{b0, b0, b0, b0, b0, b0, b1, b0},
+		[]*big.Int{b0, b0, b0, b0, b0, b0, b0, b1},
+	}
+
+	assert.Equal(t, aExpected, a)
+	assert.Equal(t, bExpected, b)
+	assert.Equal(t, cExpected, c)
+
+	b3 := big.NewInt(int64(3))
+	privateInputs := []*big.Int{b3}
+	b35 := big.NewInt(int64(35))
+	publicInputs := []*big.Int{b35}
+	// Calculate Witness
+	w, err := circuit.CalculateWitness(privateInputs, publicInputs)
+	assert.Nil(t, err)
+	b9 := big.NewInt(int64(9))
+	b27 := big.NewInt(int64(27))
+	b30 := big.NewInt(int64(30))
+	wExpected := []*big.Int{b1, b35, b3, b9, b27, b30, b35, b1}
+	assert.Equal(t, wExpected, w)
+
+	// circuitJson, _ := json.Marshal(circuit)
+	// fmt.Println("circuit:", string(circuitJson))
+
+	assert.Equal(t, circuit.NPublic, 1)
+	assert.Equal(t, len(circuit.PublicInputs), 1)
+	assert.Equal(t, len(circuit.PrivateInputs), 1)
+}
diff --git a/circuitcompiler/parser.go b/circuitcompiler/parser.go
index 70f074b..6bbf42b 100644
--- a/circuitcompiler/parser.go
+++ b/circuitcompiler/parser.go
@@ -6,6 +6,7 @@ import (
 	"io"
 	"os"
 	"regexp"
+	"strconv"
 	"strings"
 )
 
@@ -68,6 +69,12 @@ func (p *Parser) parseLine() (*Constraint, error) {
 		if err != nil {
 			return c, err
 		}
+		// get func name
+		fName := strings.Split(line, "(")[0]
+		fName = strings.Replace(fName, " ", "", -1)
+		fName = strings.Replace(fName, "	", "", -1)
+		c.V1 = fName // so, the name of the func will be in c.V1
+
 		// read string inside ( )
 		rgx := regexp.MustCompile(`\((.*?)\)`)
 		insideParenthesis := rgx.FindStringSubmatch(line)
@@ -105,20 +112,47 @@ func (p *Parser) parseLine() (*Constraint, error) {
 		c.V2 = params[1]
 		return c, nil
 	}
-	// if c.Literal == "out" {
-	//         // TODO
-	//         return c, nil
-	// }
+	if c.Literal == "return" {
+		_, varToReturn := p.scanIgnoreWhitespace()
+		c.Out = varToReturn
+		return c, nil
+	}
 
 	_, lit = p.scanIgnoreWhitespace() // skip =
 	c.Literal += lit
 
 	// v1
 	_, lit = p.scanIgnoreWhitespace()
+
+	// check if lit is a name of a func that we have declared
+	if _, ok := circuits[lit]; ok {
+		// if inside, is calling a declared function
+		c.Literal = "call"
+		c.Op = lit // c.Op handles the name of the function called
+		// put the inputs of the call into the c.PrivateInputs
+		// format: `funcname(a, b)`
+		line, err := p.s.r.ReadString(')')
+		if err != nil {
+			fmt.Println("ERR", err)
+			return c, err
+		}
+		// read string inside ( )
+		rgx := regexp.MustCompile(`\((.*?)\)`)
+		insideParenthesis := rgx.FindStringSubmatch(line)
+		varsString := strings.Replace(insideParenthesis[1], " ", "", -1)
+		params := strings.Split(varsString, ",")
+		c.PrivateInputs = params
+		return c, nil
+
+	}
+
 	c.V1 = lit
 	c.Literal += lit
 	// operator
 	_, lit = p.scanIgnoreWhitespace()
+	if lit == "(" {
+		panic(errors.New("using not declared function"))
+	}
 	c.Op = lit
 	c.Literal += lit
 	// v2
@@ -150,39 +184,67 @@ func addToArrayIfNotExist(arr []string, elem string) []string {
 	return arr
 }
 
+func subsIfInMap(original string, m map[string]string) string {
+	if v, ok := m[original]; ok {
+		return v
+	}
+	return original
+}
+
+var circuits map[string]*Circuit
+
 // Parse parses the lines and returns the compiled Circuit
 func (p *Parser) Parse() (*Circuit, error) {
-	circuit := &Circuit{}
-	circuit.Signals = append(circuit.Signals, "one")
+	// funcsMap is a map holding the functions names and it's content as Circuit
+	circuits = make(map[string]*Circuit)
+	mainExist := false
+	circuits["main"] = &Circuit{}
+	callsCount := 0
+
+	circuits["main"].Signals = append(circuits["main"].Signals, "one")
 	nInputs := 0
+	currCircuit := ""
 	for {
 		constraint, err := p.parseLine()
 		if err != nil {
 			break
 		}
 		if constraint.Literal == "func" {
+			// the name of the func is in constraint.V1
+			// check if the name of func is main
+			if constraint.V1 != "main" {
+				currCircuit = constraint.V1
+				circuits[currCircuit] = &Circuit{}
+				circuits[currCircuit].Constraints = append(circuits[currCircuit].Constraints, *constraint)
+				continue
+			}
+			currCircuit = "main"
+			mainExist = true
+			// l, _ := json.Marshal(constraint)
+			// fmt.Println(string(l))
+
 			// one constraint for each input
 			for _, in := range constraint.PublicInputs {
 				newConstr := &Constraint{
 					Op:  "in",
 					Out: in,
 				}
-				circuit.Constraints = append(circuit.Constraints, *newConstr)
+				circuits[currCircuit].Constraints = append(circuits[currCircuit].Constraints, *newConstr)
 				nInputs++
-				circuit.Signals = addToArrayIfNotExist(circuit.Signals, in)
-				circuit.NPublic++
+				circuits[currCircuit].Signals = addToArrayIfNotExist(circuits[currCircuit].Signals, in)
+				circuits[currCircuit].NPublic++
 			}
 			for _, in := range constraint.PrivateInputs {
 				newConstr := &Constraint{
 					Op:  "in",
 					Out: in,
 				}
-				circuit.Constraints = append(circuit.Constraints, *newConstr)
+				circuits[currCircuit].Constraints = append(circuits[currCircuit].Constraints, *newConstr)
 				nInputs++
-				circuit.Signals = addToArrayIfNotExist(circuit.Signals, in)
+				circuits[currCircuit].Signals = addToArrayIfNotExist(circuits[currCircuit].Signals, in)
 			}
-			circuit.PublicInputs = constraint.PublicInputs
-			circuit.PrivateInputs = constraint.PrivateInputs
+			circuits[currCircuit].PublicInputs = constraint.PublicInputs
+			circuits[currCircuit].PrivateInputs = constraint.PrivateInputs
 			continue
 		}
 		if constraint.Literal == "equals" {
@@ -193,7 +255,7 @@ func (p *Parser) Parse() (*Circuit, error) {
 				Out:     constraint.V1,
 				Literal: "equals(" + constraint.V1 + ", " + constraint.V2 + "): " + constraint.V1 + "==" + constraint.V2 + " * 1",
 			}
-			circuit.Constraints = append(circuit.Constraints, *constr1)
+			circuits[currCircuit].Constraints = append(circuits[currCircuit].Constraints, *constr1)
 			constr2 := &Constraint{
 				Op:      "*",
 				V1:      constraint.V1,
@@ -201,42 +263,64 @@ func (p *Parser) Parse() (*Circuit, error) {
 				Out:     constraint.V2,
 				Literal: "equals(" + constraint.V1 + ", " + constraint.V2 + "): " + constraint.V2 + "==" + constraint.V1 + " * 1",
 			}
-			circuit.Constraints = append(circuit.Constraints, *constr2)
+			circuits[currCircuit].Constraints = append(circuits[currCircuit].Constraints, *constr2)
+			continue
+		}
+		if constraint.Literal == "return" {
+			currCircuit = ""
+			continue
+		}
+		if constraint.Literal == "call" {
+			callsCountStr := strconv.Itoa(callsCount)
+			// for each of the constraints of the called circuit
+			// add it into the current circuit
+			signalMap := make(map[string]string)
+			for i, s := range constraint.PrivateInputs {
+				// signalMap[s] = circuits[constraint.Op].Constraints[0].PrivateInputs[i]
+				signalMap[circuits[constraint.Op].Constraints[0].PrivateInputs[i]+callsCountStr] = s
+			}
+			// add out to map
+			signalMap[circuits[constraint.Op].Constraints[len(circuits[constraint.Op].Constraints)-1].Out+callsCountStr] = constraint.Out
+
+			for i := 1; i < len(circuits[constraint.Op].Constraints); i++ {
+				c := circuits[constraint.Op].Constraints[i]
+				// add constraint, puting unique names to vars
+				nc := &Constraint{
+					Op:      c.Op,
+					V1:      subsIfInMap(c.V1+callsCountStr, signalMap),
+					V2:      subsIfInMap(c.V2+callsCountStr, signalMap),
+					Out:     subsIfInMap(c.Out+callsCountStr, signalMap),
+					Literal: "",
+				}
+				nc.Literal = nc.Out + "=" + nc.V1 + nc.Op + nc.V2
+				circuits[currCircuit].Constraints = append(circuits[currCircuit].Constraints, *nc)
+			}
+			for _, s := range circuits[constraint.Op].Signals {
+				circuits[currCircuit].Signals = addToArrayIfNotExist(circuits[currCircuit].Signals, subsIfInMap(s+callsCountStr, signalMap))
+			}
+			callsCount++
 			continue
+
 		}
-		circuit.Constraints = append(circuit.Constraints, *constraint)
+
+		circuits[currCircuit].Constraints = append(circuits[currCircuit].Constraints, *constraint)
 		isVal, _ := isValue(constraint.V1)
 		if !isVal {
-			circuit.Signals = addToArrayIfNotExist(circuit.Signals, constraint.V1)
+			circuits[currCircuit].Signals = addToArrayIfNotExist(circuits[currCircuit].Signals, constraint.V1)
 		}
 		isVal, _ = isValue(constraint.V2)
 		if !isVal {
-			circuit.Signals = addToArrayIfNotExist(circuit.Signals, constraint.V2)
+			circuits[currCircuit].Signals = addToArrayIfNotExist(circuits[currCircuit].Signals, constraint.V2)
 		}
 
-		// if constraint.Out == "out" {
-		// if Out is "out", put it after first value (one) and before the inputs
-		// if constraint.Out == circuit.PublicInputs[0] {
-		// if existInArray(circuit.PublicInputs, constraint.Out) {
-		//         // if Out is a public signal, put it after first value (one) and before the private inputs
-		//         if !existInArray(circuit.Signals, constraint.Out) {
-		//                 // if already don't exists in signal array
-		//                 signalsCopy := copyArray(circuit.Signals)
-		//                 var auxSignals []string
-		//                 auxSignals = append(auxSignals, signalsCopy[0])
-		//                 auxSignals = append(auxSignals, constraint.Out)
-		//                 auxSignals = append(auxSignals, signalsCopy[1:]...)
-		//                 circuit.Signals = auxSignals
-		//                 // circuit.PublicInputs = append(circuit.PublicInputs, constraint.Out)
-		//                 circuit.NPublic++
-		//         }
-		// } else {
-		circuit.Signals = addToArrayIfNotExist(circuit.Signals, constraint.Out)
-		// }
+		circuits[currCircuit].Signals = addToArrayIfNotExist(circuits[currCircuit].Signals, constraint.Out)
+	}
+	circuits["main"].NVars = len(circuits["main"].Signals)
+	circuits["main"].NSignals = len(circuits["main"].Signals)
+	if mainExist == false {
+		return circuits["main"], errors.New("No 'main' func declared")
 	}
-	circuit.NVars = len(circuit.Signals)
-	circuit.NSignals = len(circuit.Signals)
-	return circuit, nil
+	return circuits["main"], nil
 }
 func copyArray(in []string) []string { // tmp
 	var out []string
diff --git a/go-snark-cli b/go-snark-cli
index cc5e06b..b503f67 100755
Binary files a/go-snark-cli and b/go-snark-cli differ
diff --git a/snark_test.go b/snark_test.go
index a1c070c..9fdfeae 100644
--- a/snark_test.go
+++ b/snark_test.go
@@ -18,20 +18,37 @@ func TestZkFromFlatCircuitCode(t *testing.T) {
 
 	// circuit function
 	// y = x^3 + x + 5
-	flatCode := `
-	func test(private s0, public s1):
-		s2 = s0 * s0
-		s3 = s2 * s0
-		s4 = s3 + s0
-		s5 = s4 + 5
-		equals(s1, s5)
-		out = 1 * 1
+	code := `
+		func exp3(private a):
+			b = a * a
+			c = a * b
+			return c
+		func sum(private a, private b):
+			c = a + b
+			return c
+
+		func main(private s0, public s1):
+			s3 = exp3(s0)
+			s4 = sum(s3, s0)
+			s5 = s4 + 5
+			equals(s1, s5)
+			out = 1 * 1
 	`
-	fmt.Print("\nflat code of the circuit:")
-	fmt.Println(flatCode)
+	// the same code without the functions calling, all in one func
+	// code := `
+	// func test(private s0, public s1):
+	//         s2 = s0 * s0
+	//         s3 = s2 * s0
+	//         s4 = s3 + s0
+	//         s5 = s4 + 5
+	//         equals(s1, s5)
+	//         out = 1 * 1
+	// `
+	fmt.Print("\ncode of the circuit:")
+	fmt.Println(code)
 
 	// parse the code
-	parser := circuitcompiler.NewParser(strings.NewReader(flatCode))
+	parser := circuitcompiler.NewParser(strings.NewReader(code))
 	circuit, err := parser.Parse()
 	assert.Nil(t, err)
 	// fmt.Println("\ncircuit data:", circuit)
@@ -47,8 +64,8 @@ func TestZkFromFlatCircuitCode(t *testing.T) {
 	w, err := circuit.CalculateWitness(privateInputs, publicSignals)
 	assert.Nil(t, err)
 
-	// flat code to R1CS
-	fmt.Println("\ngenerating R1CS from flat code")
+	// code to R1CS
+	fmt.Println("\ngenerating R1CS from code")
 	a, b, c := circuit.GenerateR1CS()
 	fmt.Println("\nR1CS:")
 	fmt.Println("a:", a)
@@ -132,16 +149,16 @@ func TestZkFromFlatCircuitCode(t *testing.T) {
 }
 
 func TestZkMultiplication(t *testing.T) {
-	flatCode := `
-	func test(private a, private b, public c):
+	code := `
+	func main(private a, private b, public c):
 		d = a * b
 		equals(c, d)
 		out = 1 * 1
 	`
-	fmt.Println("flat code", flatCode)
+	fmt.Println("code", code)
 
 	// parse the code
-	parser := circuitcompiler.NewParser(strings.NewReader(flatCode))
+	parser := circuitcompiler.NewParser(strings.NewReader(code))
 	circuit, err := parser.Parse()
 	assert.Nil(t, err)
 
@@ -155,8 +172,8 @@ func TestZkMultiplication(t *testing.T) {
 	w, err := circuit.CalculateWitness(privateInputs, publicSignals)
 	assert.Nil(t, err)
 
-	// flat code to R1CS
-	fmt.Println("\ngenerating R1CS from flat code")
+	// code to R1CS
+	fmt.Println("\ngenerating R1CS from code")
 	a, b, c := circuit.GenerateR1CS()
 	fmt.Println("\nR1CS:")
 	fmt.Println("a:", a)
@@ -242,8 +259,8 @@ func TestZkMultiplication(t *testing.T) {
 func TestMinimalFlow(t *testing.T) {
 	// circuit function
 	// y = x^3 + x + 5
-	flatCode := `
-	func test(private s0, public s1):
+	code := `
+	func main(private s0, public s1):
 		s2 = s0 * s0
 		s3 = s2 * s0
 		s4 = s3 + s0
@@ -251,11 +268,11 @@ func TestMinimalFlow(t *testing.T) {
 		equals(s1, s5)
 		out = 1 * 1
 	`
-	fmt.Print("\nflat code of the circuit:")
-	fmt.Println(flatCode)
+	fmt.Print("\ncode of the circuit:")
+	fmt.Println(code)
 
 	// parse the code
-	parser := circuitcompiler.NewParser(strings.NewReader(flatCode))
+	parser := circuitcompiler.NewParser(strings.NewReader(code))
 	circuit, err := parser.Parse()
 	assert.Nil(t, err)
 
@@ -268,8 +285,8 @@ func TestMinimalFlow(t *testing.T) {
 	w, err := circuit.CalculateWitness(privateInputs, publicSignals)
 	assert.Nil(t, err)
 
-	// flat code to R1CS
-	fmt.Println("\ngenerating R1CS from flat code")
+	// code to R1CS
+	fmt.Println("\ngenerating R1CS from code")
 	a, b, c := circuit.GenerateR1CS()
 	fmt.Println("\nR1CS:")
 	fmt.Println("a:", a)