_expr :: Parser (AST' Text)
bind_expr = Bind
    <$> identifier
    <*  reservedOp "<~"
    <*> expr
    <*> expr

le
bind_expr :: Parser (AST' Text)
bind_expr = Bind
    <$> identifier
    <*  reservedOp "<~"
    <*> expr
    <*> expr
bind_expr = Bind
    <$> identifier
    <*  reservedOp "<~"
    <*> expr
    <*> expr