1 files changed, 45 insertions, 0 deletions
diff --git a/execute.go b/execute.go
new file mode 100644
index 0000000..8062d32
--- /dev/null
+++ b/execute.go
@@ -0,0 +1,45 @@
+package expression
+
+import (
+	"fmt"
+	"go/token"
+	"strings"
+)
+
+func (e *Evaluator) execute(tokens chan Token) (any, error) {
+	stack := Stack{}
+	for tok := range tokens {
+		switch {
+		case tok.IsNumber():
+			stack.Push(tok)
+		case tok.IsOperator():
+			op := e.operators[tok.Token]
+			if err := op.fn(&stack); err != nil {
+				return nil, err
+			}
+		case tok.IsFunc():
+			fn, fnEsist := e.functions[strings.ToLower(tok.Literal)]
+			if !fnEsist {
+				return nil, fmt.Errorf("unknown function %s at %d", tok.Literal, tok.Pos)
+			}
+			if err := fn(&stack); err != nil {
+				return nil, err
+			}
+		case tok.IsError():
+			return nil, fmt.Errorf("Error at token %d: %w", tok.Pos, tok.Error())
+		}
+	}
+	if len(stack) != 1 {
+		return nil, fmt.Errorf("Expected exact one returning value, go %+v", stack)
+	}
+	result := stack.Pop()
+	switch result.Token {
+	case token.INT:
+		n, _ := result.Int()
+		return n, nil
+	case token.FLOAT:
+		return result.Float(), nil
+	default:
+		return result.Literal, nil
+	}
+}