expr :: Parser (AST' Text)
lam_expr =
    reserved "fn"
    *>  (Lam
        <$> identifier
        <*> type_expr
        <*> semiblockExpr
        )

bi
lam_expr :: Parser (AST' Text)
lam_expr =
    reserved "fn"
    *>  (Lam
        <$> identifier
        <*> type_expr
        <*> semiblockExpr
        )
lam_expr =
    reserved "fn"
    *>  (Lam
        <$> identifier
        <*> type_expr
        <*> semiblockExpr
        )