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/Lexer.hs

@@ -1,32 +1,17 @@
 module Lexer where
 
 import Research
+
+import Control.Monad               (void)
+import Data.Void
 import Text.Megaparsec
 import Text.Megaparsec.Char hiding (space)
 import Text.Megaparsec.Char.Lexer
 
-import Control.Monad (void)
-import Data.Void
-
 import qualified Data.Set as Set
 
 type Lexer = Parsec Void String
 
-data LToken
-  = LKeywordT
-  | LIdentifier String
-  | LIntegerLiteral Int
-  | LStringLiteral String
-  | LAssign
-  | LColon
-  | LBackslash
-  | LOpenParen
-  | LCloseParen
-  | LOpenBracket
-  | LCloseBracket
-  | LNewline
-  deriving (Show, Eq, Ord)
-
 keywordT :: Lexer LToken
 keywordT = string "t" *> notFollowedBy alphaNumChar *> pure LKeywordT