Lesson4

Author: seanhess

app/Lesson4DataTypes.hs

@@ -1,5 +1,11 @@
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE OverloadedRecordDot #-}
+{-# LANGUAGE NoFieldSelectors #-}
+
 module Lesson4DataTypes where
 
+import Data.Time.Clock (UTCTime)
+
 -- Algebraic Data Types!
 
 -- Sum types: like enums
@@ -12,23 +18,23 @@ data Bool' = True' | False'
 -- Product types: combine different data
 -- compare to tuples in Lesson3: feI :: (String, Float)
 type Wavelength = Float
-data SpectralLine = SpectralLine Element Wavelength
+data SpectralLine1 = SpectralLine1 Element Wavelength
 
-lines :: [SpectralLine]
+lines :: [SpectralLine1]
 lines = [heI, feI, ha, caII_854]
  where
-  heI = SpectralLine He 10830
-  feI = SpectralLine Fe 6302
-  ha = SpectralLine H 6562
-  caII_854 = SpectralLine Ca 8542
+  heI = SpectralLine1 He 10830
+  feI = SpectralLine1 Fe 6302
+  ha = SpectralLine1 H 6562
+  caII_854 = SpectralLine1 Ca 8542
 
 -- We can combine the two to handle complex states!
 data HasElement = None | Has Element
 
 -- (Note: this is exactly how Maybe works, just with a type variable)
 -- data Maybe a = Nothing | Just a
 
--- *** MAKE IMPOSSIBLE STATES IMPOSSIBLE! ***
+-- *** MAKE IMPOSSIBLE STATES IMPOSSIBLE (to represent)! ***
 
 -- Example 1. Wait, are we working in Angstroms or Nanometers?
 pleaseDontCallWithAngstroms :: Wavelength -> Float
@@ -59,20 +65,20 @@ badLineName :: SpectralLineBad2 -> String
 -- what is the name of Ca Nothing?
 badLineName (SpectralLineBad2 He Nothing) = "Helium"
 badLineName (SpectralLineBad2 H Nothing) = "Hydrogen"
-badLineName (SpectralLineBad2 Fe Nothing) = "Iron"
-badLineName (SpectralLineBad2 Ca (Just CaII_849)) = "Calcium 849"
-badLineName (SpectralLineBad2 Ca (Just CaII_852)) = "Calcium 849"
-badLineName (SpectralLineBad2 Ca (Just CaII_866)) = "Calcium 849"
+badLineName (SpectralLineBad2 Fe Nothing) = "Iron I"
+badLineName (SpectralLineBad2 Ca (Just CaII_849)) = "Calcium II 849"
+badLineName (SpectralLineBad2 Ca (Just CaII_852)) = "Calcium II 852"
+badLineName (SpectralLineBad2 Ca (Just CaII_866)) = "Calcium II 866"
 
 -- Better: create an ADT that models the states exactly
-data SpectralLine'
+data SpectralLine
   = HeliumI
   | HydrogenAlpha
   | IronI
   | CalciumII CaIILine
 
-lines' :: [SpectralLine']
-lines' =
+allLines :: [SpectralLine]
+allLines =
   [ HeliumI
   , HydrogenAlpha
   , IronI
@@ -84,16 +90,177 @@ lines' =
 -- Instead of putting the wavelength and element in the datatype, now we can calculate it from the Line
 -- Impossible to represent Helium + a calcium band
 -- Or calcium without one
-element :: SpectralLine' -> Element
+element :: SpectralLine -> Element
 element HeliumI = He
 element HydrogenAlpha = H
 element IronI = Fe
 element (CalciumII _) = Ca
 
-wavelength :: SpectralLine' -> Float
-wavelength HeliumI = 10830
-wavelength HydrogenAlpha = 6562
-wavelength IronI = 6302
-wavelength (CalciumII CaII_849) = 8498
-wavelength (CalciumII CaII_852) = 8542
-wavelength (CalciumII CaII_866) = 8662
+wavelength :: SpectralLine -> Nanometers
+wavelength HeliumI = Nanometers 108.30
+wavelength HydrogenAlpha = Nanometers 656.2
+wavelength IronI = Nanometers 630.2
+wavelength (CalciumII CaII_849) = Nanometers 849.8
+wavelength (CalciumII CaII_852) = Nanometers 854.2
+wavelength (CalciumII CaII_866) = Nanometers 866.2
+
+-- Records: let you name fields
+data SpatialPixel = SpatialPixel
+  { x :: Int
+  , y :: Int
+  , luminosity :: Float
+  }
+
+data SpatialImage = SpatialImage
+  { wavelength :: Nanometers
+  , pixels :: [SpatialPixel]
+  }
+
+-- Use "." to access fields
+findVerticalLine :: Int -> SpatialImage -> [Float]
+findVerticalLine y img =
+  map (.luminosity) $ filter (\px -> px.y == y) img.pixels
+
+-- TODO: Exercise: Model an observation frame for the various instruments.
+-- This model forces us to handle weird edge cases deep in our code!
+-- Improve it as much as possible
+data ObservationFrame = ObservationFrame
+  { observationId :: String
+  , proposalId :: String
+  , dateTime :: String
+  , instrument :: String
+  , -- ViSP has 0 spatial images
+    -- VBI has N spatial images
+    -- Cryo has 1 spatial image
+    spatialImages :: [SpatialImage]
+  , -- ViSP has 3 spectral images
+    -- Cryo has 1
+    -- VBI has 0
+    spectralImage1 :: Maybe SpectralImage
+  , spectralImage2 :: Maybe SpectralImage
+  , spectralImage3 :: Maybe SpectralImage
+  }
+
+-- TODO: define SpectralImage
+data SpectralImage = SpectralImage
+
+-- TODO: Fix me!
+-- Why is this problematic?
+-- If we model the data poorly we have to check for data issues every time we access them
+-- And we keep having to deal with edge conditions everywhere!
+processCryo :: [ObservationFrame] -> [String]
+processCryo frames =
+  let cfs = filter isCryo frames
+      wls = map cryoSpatialWavelength cfs
+   in map handleWavelength wls
+ where
+  isCryo f = f.instrument == "Cryo"
+
+  handleWavelength :: Maybe Nanometers -> String
+  handleWavelength Nothing = "ERROR, Cryo missing wavelength!"
+  handleWavelength (Just (Nanometers wl)) = "Looks good: " ++ show wl
+
+  cryoSpatialWavelength :: ObservationFrame -> Maybe Nanometers
+  cryoSpatialWavelength frame =
+    case frame.spatialImages of
+      [img] -> Just img.wavelength
+      -- TODO: what do we do if a cryo frame doesn't have an image?
+      [] -> Nothing
+      -- TODO: what do we do if a cryo frame has multiple images?
+      imgs -> Nothing
+
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+--
+-- DONE: Solution
+-- (note) the ticks after names (like Instrument') are to avoid conflicts with definitions
+-- you might write during your solution. This is common practice in haskell when you have a
+-- variation on a type
+
+newtype ObservationId' = ObservationId' String
+newtype ProposalId' = ProposalId' String
+
+data Instrument'
+  = Cryo' SpatialImage SpectralImage
+  | VBI' [SpatialImage]
+  | ViSP' ViSPObservation -- It can be useful to have a record with named fields
+
+data ViSPObservation = ViSPObservation
+  { arm1 :: SpectralImage
+  , arm2 :: SpectralImage
+  , arm3 :: SpectralImage
+  }
+
+data ObservationFrame' = ObservationFrame'
+  { observationId :: ObservationId'
+  , proposalId :: ProposalId'
+  , dateTime :: UTCTime
+  , instrument :: Instrument'
+  }
+
+processAll :: [ObservationFrame'] -> [String]
+processAll frames =
+  map processFrame $ map (.instrument) frames
+ where
+  processFrame :: Instrument' -> String
+  processFrame (Cryo' spatial spectral) = processCryo spatial spectral
+  processFrame (VBI' imgs) = processVBI imgs
+  processFrame (ViSP' visp) = processViSP visp
+
+  processCryo :: SpatialImage -> SpectralImage -> String
+  processCryo img _ = handleWavelength img.wavelength
+
+  processVBI :: [SpatialImage] -> String
+  processVBI _ = "processed VBI differently!"
+
+  processViSP :: ViSPObservation -> String
+  processViSP _ = "processed VISP differently!"
+
+  handleWavelength :: Nanometers -> String
+  handleWavelength (Nanometers wl) = "Looks good: " ++ show wl

learn-haskell.cabal

@@ -34,4 +34,5 @@ executable learn-haskell
   build-depends:
       base >=4.16
     , text
+    , time
   default-language: GHC2021

package.yaml

@@ -21,6 +21,7 @@ ghc-options:
 dependencies:
   - base >= 4.16
   - text
+  - time
 
 executables:
   learn-haskell: