Add "SimpleT" t output form

This new output form allows easy piping to the decode function of the
tricu executable. Includes a new test for roundtrip evaluation of map,
compilation to tree calculus terms, and decoding back to a human
readable string.

src/Parser.hs

@@ -1,33 +1,19 @@
 module Parser where
 
 import Lexer
-import Research hiding (toList)
+import Research hiding       (toList)
 
-import Data.List.NonEmpty (toList)
+import Data.List.NonEmpty    (toList)
 import Data.Void (Void)
 import Text.Megaparsec
 import Text.Megaparsec.Char
-import Text.Megaparsec.Error (errorBundlePretty, ParseErrorBundle)
+import Text.Megaparsec.Error (ParseErrorBundle, errorBundlePretty)
 
 import qualified Data.Set as Set
 
 type Parser    = Parsec Void [LToken]
 type AltParser = Parsec Void String
 
-data TricuAST
-  = SVar String
-  | SInt Int
-  | SStr String
-  | SList [TricuAST]
-  | SFunc String [String] TricuAST
-  | SApp TricuAST TricuAST
-  | TLeaf
-  | TStem TricuAST
-  | TFork TricuAST TricuAST
-  | SLambda [String] TricuAST
-  | SEmpty
-  deriving (Show, Eq, Ord)
-
 parseTricu :: String -> [TricuAST]
 parseTricu input
   | null tokens = []