Add all the files from the interpreter repo

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

pkg/ast/if_expression.go

@@ -0,0 +1,31 @@
+package ast
+
+import (
+	"bytes"
+
+	"code.jmug.me/jmug/interpreter-in-go/pkg/token"
+)
+
+type IfExpression struct {
+	Token       token.Token // The `if` token.
+	Condition   Expression
+	Consequence *BlockStatement
+	Alternative *BlockStatement
+}
+
+func (ie *IfExpression) expressionNode() {}
+func (ie *IfExpression) TokenLiteral() string {
+	return ie.Token.Literal
+}
+func (ie *IfExpression) String() string {
+	var out bytes.Buffer
+	out.WriteString("if")
+	out.WriteString(ie.Condition.String())
+	out.WriteString(" ")
+	out.WriteString(ie.Consequence.String())
+	if ie.Alternative != nil {
+		out.WriteString("else ")
+		out.WriteString(ie.Alternative.String())
+	}
+	return out.String()
+}