feat(parser): first binary expressions

consts/expressions.go

@@ -1 +1,34 @@
 package consts
+
+type Expression interface {
+	Eval() float64
+}
+type PlusExpression struct {
+	Lhs Expression
+	Rhs Expression
+}
+type MinusExpression struct {
+	Lhs Expression
+	Rhs Expression
+}
+type MultiplicationExpression struct {
+	Lhs Expression
+	Rhs Expression
+}
+type DivisionExpression struct {
+	Lhs Expression
+	Rhs Expression
+}
+
+func (e PlusExpression) Eval() float64 {
+	return e.Lhs.Eval() + e.Rhs.Eval()
+}
+func (e MinusExpression) Eval() float64 {
+	return e.Lhs.Eval() - e.Rhs.Eval()
+}
+func (e MultiplicationExpression) Eval() float64 {
+	return e.Lhs.Eval() * e.Rhs.Eval()
+}
+func (e DivisionExpression) Eval() float64 {
+	return e.Lhs.Eval() / e.Rhs.Eval()
+}

lexer/lexer.go

@@ -167,7 +167,6 @@ func (s *Scanner) Start() []consts.Token {
 					token = append(token, s.buildToken(res, v, v, pos))
 				} else {
 					token = append(token, s.buildToken(consts.IDENTIFIER, v, v, pos))
-					// s.error(v, "unknown identifier, view https://github.com/xnacly/emmy for the complete reference")
 				}
 				continue
 			} else {

parser/parser.go

@@ -19,4 +19,32 @@ func (p *Parser) NewInput(in []consts.Token) *Parser {
 	return p
 }
 
-func (p *Parser) parse() {}
+func (p *Parser) Parse() []consts.Expression {
+	stmts := make([]consts.Expression, 0)
+	for !p.isAtEnd() {
+		stmts = append(stmts, p.statment())
+	}
+	return stmts
+}
+
+func (p *Parser) statment() consts.Expression {
+	return nil
+}
+
+func (p *Parser) peek() consts.Token {
+	return p.input[p.pos]
+}
+
+func (p *Parser) prev() consts.Token {
+	return p.input[p.pos-1]
+}
+
+func (p *Parser) advance() {
+	if !p.isAtEnd() {
+		p.pos++
+	}
+}
+
+func (p *Parser) isAtEnd() bool {
+	return p.pos >= len(p.input)
+}