__   __ __  __  ____   ___      _________________________________________
||   || ||  || ||  || ||__      Hugs 98: Based on the Haskell 98 standard
||___|| ||__|| ||__||  __||     Copyright (c) 1994-2005
||---||         ___||           World Wide Web: http://haskell.org/hugs
||   ||                         Report bugs to: hugs-bugs@haskell.org
||   || Version: March 2005     _________________________________________

Hugs mode: Restart with command line option +98 for Haskell 98 mode

Type :? for help
Let5> Bin (Bin (Const 4) Times (Bin (Const 7) Plus (Const 1))) Minus (Const 1)
Let5> Let ("a" :=: Bin (Bin (Const 4) Times (Bin (Const 7) Plus (Const 1))) Minus (Const 1)) (Bin (Var "a") Times (Var "a"))
Let5> 
Program error: user error (
*** lexical error at (line 2, column 13):
    a = 4 * [7 + 1 - 1)
            ^
 in a * a
<end of input>
)

Let5> 
Program error: user error (
*** syntax error at (line 3, column 3):
 in a * a
  ^
<end of input>
)

Let5> [Leaving Hugs]
