Parsing statements (skipping expressions).

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

pkg/ast/ast.go

@@ -0,0 +1,59 @@
+package ast
+
+import "code.jmug.me/jmug/interpreter-in-go/pkg/token"
+
+type Node interface {
+	TokenLiteral() string
+}
+
+type Statement interface {
+	Node
+	statementNode()
+}
+
+type Expression interface {
+	Node
+	expressionNode()
+}
+
+type Program struct {
+	Statements []Statement
+}
+
+func (p *Program) TokenLiteral() string {
+	if len(p.Statements) > 0 {
+		return p.Statements[0].TokenLiteral()
+	}
+	return ""
+}
+
+type LetStatement struct {
+	Token token.Token // TODO: This is a little redundant, figure out if I can get rid of it.
+	Name  *Identifier
+	Value Expression
+}
+
+func (ls *LetStatement) statementNode() {}
+func (ls *LetStatement) TokenLiteral() string {
+	return ls.Token.Literal
+}
+
+type ReturnStatement struct {
+	Token       token.Token // TODO: This is a little redundant, figure out if I can get rid of it.
+	ReturnValue Expression
+}
+
+func (rs *ReturnStatement) statementNode() {}
+func (rs *ReturnStatement) TokenLiteral() string {
+	return rs.Token.Literal
+}
+
+type Identifier struct {
+	Token token.Token
+	Value string
+}
+
+func (i *Identifier) expressionNode() {}
+func (i *Identifier) TokenLiteral() string {
+	return i.Token.Literal
+}