add function eval to evaluate a string to an expression

Author: seborama

README.md

@@ -152,7 +152,7 @@ This is container `Value`. It can contain zero or any number of `Value`'s. Curre
 * Types: String, Number, Bool, MultiValue
 * Associativity with parentheses: `(` and `)`
 * Functions:
-    * Built-in: pi, cos, floor, sin, sqrt, trunc, and more (see `function.go`: `Eval()`)
+    * Built-in: pi, cos, floor, sin, sqrt, trunc, **eval**, and more (see `function.go`: `Eval()`)
     * User-defined, injected via `WithFunctions()`
 * Variables, defined as `:variable_name:` and injected via `WithVariables()`
 

function.go

@@ -64,6 +64,7 @@ var builtInFunctions = map[string]FunctionalValue{
 	"trunc":     Trunc,
 	"ln":        Ln,
 	"log":       Log,
+	"eval":      Eval,
 }
 
 // BuiltInFunction returns a built-in function body if known.
@@ -241,3 +242,17 @@ func Trunc(args ...Value) Value {
 
 	return NewUndefinedWithReasonf("trunc(): invalid argument #1 '%s'", argVal.String())
 }
+
+func Eval(args ...Value) Value {
+	if len(args) != 1 {
+		return NewUndefinedWithReasonf("eval() requires 1 argument1, got %d: '%v'", len(args), args)
+	}
+
+	argVal := args[0]
+
+	if v, ok := argVal.(Evaler); ok {
+		return v.Eval()
+	}
+
+	return argVal
+}

function_test.go

@@ -7,6 +7,7 @@ import (
 	"github.com/seborama/gal/v8"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestPi(t *testing.T) {
@@ -76,3 +77,11 @@ func TestLog(t *testing.T) {
 	val = gal.Log(gal.NewNumber(10_000_000), gal.NewNumber(0))
 	assert.Equal(t, "7", val.String())
 }
+
+func TestFunctionEval(t *testing.T) {
+	expr := `eval("7+22")*2`
+	tree, err := gal.NewTreeBuilder().FromExpr(expr)
+	require.NoError(t, err)
+
+	assert.Equal(t, "58", tree.Eval().String())
+}

tree_builder_test.go

@@ -1,6 +1,7 @@
 package gal_test
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -10,24 +11,24 @@ import (
 )
 
 func TestTreeBuilder_FromExpr_VariousOperators(t *testing.T) {
-	expr := `-1 + 2 * 3 / 2 + 3 ** 2 -8`
+	expr := `-10 + 2 * 7 / 2 + 5 ** 4 -8`
 	tree, err := gal.NewTreeBuilder().FromExpr(expr)
 	require.NoError(t, err)
 
 	expectedTree := gal.Tree{
 		gal.NewNumber(-1),
 		gal.Multiply,
-		gal.NewNumber(1),
+		gal.NewNumber(10),
 		gal.Plus,
 		gal.NewNumber(2),
 		gal.Multiply,
-		gal.NewNumber(3),
+		gal.NewNumber(7),
 		gal.Divide,
 		gal.NewNumber(2),
 		gal.Plus,
-		gal.NewNumber(3),
+		gal.NewNumber(5),
 		gal.Power,
-		gal.NewNumber(2),
+		gal.NewNumber(4),
 		gal.Minus,
 		gal.NewNumber(8),
 	}
@@ -41,6 +42,7 @@ func TestTreeBuilder_FromExpr_PlusMinus_String(t *testing.T) {
 	expr := `"-3 + -4" + -3 --4 / ( 1 + 2+3+4) +tan(10)`
 	tree, err := gal.NewTreeBuilder().FromExpr(expr)
 	require.NoError(t, err)
+	fmt.Println(tree.Eval())
 
 	expectedTree := gal.Tree{
 		gal.NewString(`-3 + -4`),

value.go

@@ -21,6 +21,10 @@ type Booler interface {
 	Bool() Bool
 }
 
+type Evaler interface {
+	Eval() Value
+}
+
 // TODO: we may also want to create ToString() and ToBool()
 func ToNumber(val Value) Number {
 	// TODO: we could also try to convert Bool to Number since we could add NewNumberFromBool() to deal with Bool's
@@ -191,6 +195,15 @@ func (s String) Number() Number {
 	return n
 }
 
+func (s String) Eval() Value {
+	tree, err := NewTreeBuilder().FromExpr(s.value)
+	if err != nil {
+		return s
+	}
+
+	return tree.Eval()
+}
+
 type Number struct {
 	Undefined
 	value decimal.Decimal