Fixes #412 by adding modes and cleaning up build.sh

build.sh

 #!/bin/sh
 set -e
+set -x
+
+function print_help {
+  echo "Run build.sh from inside the IHaskell directory to install packages in this repository:"
+  echo "  ./build.sh ihaskell # Install IHaskell and its dependencies"
+  echo "  ./build.sh quick    # Install IHaskell, but not its dependencies"
+  echo "  ./build.sh all      # Install IHaskell, dependencies, and all display packages"
+  echo "  ./build.sh display  # Install IHaskell and display libraries"
+  echo
+  echo "If this is your first time installing IHaskell, run './build.sh ihaskell'."
+}
 
 # Verify that we're in the IHaskell directory.
 if [ ! -e ihaskell.cabal ]; then
-  echo "Run build.sh from inside the IHaskell directory:"
-  echo "  ./build.sh all      # Install IHaskell and deps (use if first install)"
-  echo "  ./build.sh          # Install only IHaskell, no deps"
-  echo "  ./build.sh display  # Install IHaskell and display libraries"
+  print_help;
+  exit 1
+fi
+
+if [ $# -lt 1 ]; then
+    print_help;
     exit 1
 fi
 
+if [ ! $1 = "all" ] || [ ! $1 = "ihaskell" ] || [ ! $1 = "display" ] || [ ! $1 = "quick" ]; then
+    print_help;
+    exit 1;
+fi
+
 # What to install.
 INSTALLS=""
 
@@ -18,17 +36,17 @@ rm -rf ~/.ipython/kernels/haskell
 
 # Compile dependencies.
 if [ $# -gt 0 ]; then
-  if [ $1 = "all" ]; then
+  if [ $1 = "all" ] || [ $1 = "ihaskell" ]; then
     INSTALLS="$INSTALLS ghc-parser ipython-kernel"
   fi
 fi
 
-# Make ihaskell itself
+# Always make ihaskell itself
 INSTALLS="$INSTALLS ."
 
 # Install ihaskell-display packages.
 if [ $# -gt 0 ]; then
-  if [ $1 = "display" ]; then
+  if [ $1 = "display" ] || [ $1 = "all" ]; then
         # Install all the display libraries
         # However, install ihaskell-diagrams separately...
         cd ihaskell-display
@@ -60,7 +78,8 @@ fi
 
 # Finish installing ihaskell-diagrams.
 if [ $# -gt 0 ]; then
-  if [ $1 = "display" ]; then
+  if [ $1 = "display" ] || [ $1 = "all" ]; then
+      echo 'Installing IHaskell diagrams support.'
       cabal install -j ihaskell-display/ihaskell-diagrams --force-reinstalls --constraint "arithmoi==0.4.*"
     fi
 fi