Parse function literals.

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

pkg/ast/function.go

@@ -0,0 +1,32 @@
+package ast
+
+import (
+	"bytes"
+	"strings"
+
+	"code.jmug.me/jmug/interpreter-in-go/pkg/token"
+)
+
+type FunctionLiteral struct {
+	Token      token.Token // The fn token
+	Parameters []*Identifier
+	Body       *BlockStatement
+}
+
+func (fl *FunctionLiteral) expressionNode() {}
+func (fl *FunctionLiteral) TokenLiteral() string {
+	return fl.Token.Literal
+}
+func (fl *FunctionLiteral) String() string {
+	var out bytes.Buffer
+	params := []string{}
+	for _, p := range fl.Parameters {
+		params = append(params, p.String())
+	}
+	out.WriteString(fl.TokenLiteral())
+	out.WriteString("(")
+	out.WriteString(strings.Join(params, ", "))
+	out.WriteString(") ")
+	out.WriteString(fl.Body.String())
+	return out.String()
+}