diff --git a/README.md b/README.md
index c538cbe..58f4d9c 100644
--- a/README.md
+++ b/README.md
@@ -20,30 +20,53 @@ Then, you can put the file gomath where do you want (it could be in `/usr/local/
 
 ### Calculate
 
-To parse an expression and calculate it, use `gomath.ParseAndCalculate(string, *gomath.Options) (string, error)`.
+To parse an expression, use `gomath.Parse(string) (gomath.Result, error)`.
 The string is a valid expression, like `1+2` or `2(1/3+4)^5`.
-It returns the result of the expression in a string according to the given options.
+
+The result will give you everything needed to perform operations, like getting the exact representation of the result, 
+or the ability to convert
 
 ```go
-res, err := gomath.ParseAndCalculate("1+2", &gomath.Options{})
-err == nil // true
-res == "3" // true
+res, err := gomath.Parse("1/2+1")
+// check the error
+res.String == "3/2" // true
+res.IsExact // true because 1.5 is the exact representation of 3/2
+res.LaTeX == `\frac{1}{2} + 1` // true
+res.Approx(5) == "1.50000" // true
 ```
 
-You can modify the result's type with `gomath.Options`.
-Set `Decimal` to `true` if you want to have a decimal approximation.
-You can specify the number of digits with `Precision`.
+You can also call `gomath.ParseAndCalculate(string, *gomath.Options) (string, error)` to directly get the string 
+representation with the given options or `gomath.ParseAndConvertToLatex(string, *gomath.Options) (string, error)` to get
+the $\LaTeX$ code.
+
+### Creating a function
 
-### Convert to LaTeX
+You can create a function with `gomath.NewFunction(string) (gomath.Function, int, error)`.
+The string is a valid expression representing a function.
+It is composed by the arguments and the expression of the function.
+You must separate each argument with a coma (`,`) and separate the arguments and the expression with `->`.
+```
+x, y -> x^y
+```
+is a valid expression representing a function.
+The returned int is the number of arguments.
 
-To parse an expression and convert it into $\LaTeX$, use `gomath.ParseAndConvertToLatex(string, *gomath.Options) (string, error)`.
-The string is a valid expression like `1+2` or `2(1/3+4)^5`.
-It returns the result of the expression in a string according to the given options.
+Then, you can evaluate the function by passing a map containing every argument.
+gomath will send you the result (an instance of `gomath.Result`) of the evaluation.
 
 ```go
-res, err := gomath.ParseAndConvertToLatex("(1+2/3)/2", &gomath.Options{})
-err == nil // true
-res == `\frac{1 + \frac{2}{3}}{2}` // true
+f, _, err := gomath.NewFunction("x, y -> x^y")
+if err != nil {
+	panic(err) // will not panic because the expression is valid
+}
+res, err := f(map[string]string{
+	"x": "5",
+	"y": "2"
+})
+if err != nil {
+	panic(err) // will not panic because the expression is valid and every argument is set
+}
+res.String == "25" // true
 ```
 
 ### CLI
diff --git a/function.go b/function.go
new file mode 100644
index 0000000..fe28432
--- /dev/null
+++ b/function.go
@@ -0,0 +1,50 @@
+package gomath
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+var (
+	ErrInvalidFunction     = errors.New("invalid function")
+	ErrInvalidFunctionCall = errors.New("invalid function call")
+)
+
+type Function func(map[string]string) (Result, error)
+
+// NewFunction creates a new Function by parsing the given string. It must follow this scheme:
+//
+//	arg1, arg2, arg3... -> expr
+//
+// Example:
+//
+//	gomath.NewFunction("x, y -> x^y")
+//
+// It returns the Function and the number of arguments.
+func NewFunction(s string) (Function, int, error) {
+	splits := strings.Split(s, "->")
+	if len(splits) != 2 {
+		return nil, 0, errors.Join(ErrInvalidFunction, errors.New("a function is defined by 'args -> expression'"))
+	}
+	before := splits[0]
+	expression := strings.TrimSpace(splits[1])
+	var params []string
+	for _, p := range strings.Split(before, ",") {
+		params = append(params, strings.TrimSpace(p))
+	}
+	return func(args map[string]string) (Result, error) {
+		if len(params) != len(args) {
+			return nil, errors.Join(ErrInvalidFunctionCall, errors.New("not all parameters have been defined"))
+		}
+		cp := expression
+		for _, p := range params {
+			v, ok := args[p]
+			if !ok {
+				return nil, errors.Join(ErrInvalidFunctionCall, fmt.Errorf("missing argument for %s", p))
+			}
+			cp = strings.ReplaceAll(cp, p, v)
+		}
+		return Parse(cp)
+	}, len(params), nil
+}
diff --git a/function_test.go b/function_test.go
new file mode 100644
index 0000000..efb043c
--- /dev/null
+++ b/function_test.go
@@ -0,0 +1,35 @@
+package gomath
+
+import "testing"
+
+func TestNewFunction(t *testing.T) {
+	f, n, err := NewFunction("x -> x^2")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 1 {
+		t.Errorf("got %d, want 1", n)
+	}
+	result, err := f(map[string]string{"x": "5"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.String() != "25" {
+		t.Errorf("got %s, want 25", result.String())
+	}
+
+	f, n, err = NewFunction("x, y -> x^y")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 2 {
+		t.Errorf("got %d, want 2", n)
+	}
+	result, err = f(map[string]string{"x": "5", "y": "2"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.String() != "25" {
+		t.Errorf("got %s, want 25", result.String())
+	}
+}