How to specify an extra lib during a port build?

[Yuri]

Here's the port Makefile that leads to the error:


# $FreeBSD$

PORTNAME=    penrose
DISTVERSIONPREFIX=    v
DISTVERSION=    0.1.1.1
CATEGORIES=    math haskell

MAINTAINER=    yuri at FreeBSD.org
COMMENT=    Create beautiful diagrams by typing mathematical notation in 
plain text

LICENSE=    BSD3CLAUSE

USES=        cabal
USE_GITHUB=    yes

.include <bsd.port.mk>


Yuri