refactor how repl works

internal/parser/parser.go

@@ -61,6 +61,7 @@ type (
 )
 
 type Parser struct {
+	fn     string
 	l      *lexer.Lexer
 	errors []string
 
@@ -71,8 +72,9 @@ type Parser struct {
 	infixParseFns  map[token.TokenType]infixParseFn
 }
 
-func New(l *lexer.Lexer) *Parser {
+func New(fn string, l *lexer.Lexer) *Parser {
 	p := &Parser{
+		fn:     fn,
 		l:      l,
 		errors: []string{},
 	}
@@ -619,3 +621,11 @@ func (p *Parser) parseImportExpression() ast.Expression {
 
 	return expression
 }
+
+// Parse parses the input source into a top-level AST for either evaluation
+// or compilation to bytecode. The parameter fn denotes the filename the source
+// originated from.
+func Parse(fn, input string) (prog ast.Node, errors []string) {
+	p := New(fn, lexer.New(input))
+	return p.ParseProgram(), p.Errors()
+}