install FLASK in a conda environment

flask-in-conda.sh

# create and activate a new environment for flask
conda create -n flask
conda activate flask

# switch to the root of the environment
cd $CONDA_PREFIX

# use ONLY conda-forge for packages
echo 'channels: [conda-forge]' > .condarc

# install the compilers package and dependencies
conda install compilers cfitsio gsl

# create a folder for non-package dependencies
mkdir opt
cd opt

# download and extract HEALPix 3.70
curl -OL https://downloads.sourceforge.net/project/healpix/Healpix_3.70/Healpix_3.70_2020Jul23.tar.gz
tar xf Healpix_3.70_2020Jul23.tar.gz
cd Healpix_3.70

# build libsharp (HEALPix dependency) and install into conda environment
cd src/common_libraries/libsharp/
./configure --prefix=$CONDA_PREFIX
make install

# build healpix_cxx and install into conda environment
cd ../../cxx
./configure --prefix=$CONDA_PREFIX
make install

# now download and extract FLASK wherever you want;
# in src/Makefile, set the following (look through
# the file, all of these are already set):
# 
#     COMP = $(CXX) $(CXXFLAGS) $(LDFLAGS) $(DEBUG)
#
#     HEALDIR  = $(CONDA_PREFIX)/opt/Healpix_3.70
#     HEALDATA = $(HEALDIR)/data
#     CXXHEAL  = -I$(CONDA_PREFIX)/include/healpix_cxx
#     LDHEAL   =
#
#     LIB1 =
#     LIB2 =
#
#     LIBHEALPIX = -lhealpix_cxx
#     LIBSHARP = -lsharp
#
# then cd into src/ and make