Show values for Lists

`unwordsList :: [LispVal] -> String` composes three functions:
* `map :: (a -> b) -> [a] -> [b]` a function with two "arguments"[0], a
  function `(a -> b)` and a list of `a`s (`[a]`) and returns a `[b]`, i.e.
  it applies the function in the first argument to every element of the
  second
* `showAll :: LispVal -> String` described in the previous commit.
  `map showAll` returns a function that applies `showAll` to each
  element of the list it gets.
* `unwords :: [String] -> String` which joins a list of Strings with
  spaces.

The `.` dot operator is used to pass the output of rhs to the input of
lhs. So in essence, `unwordsList` is a function that will `unword` the
list of Strings returned by `map`ing `showVal` to the list of `LispVal`s
passed to `unwordsList`.

[0] Remember that all functions are curried, and actually only take one
argument and return a "partial function" that takes the next argument.

diff --git a/app/Main.hs b/app/Main.hs
index 1495605d09602a2ed23717d3b5956402874a6ef4..996f9211119591408d07062b610928ba5d5dddff 100644 (file)
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -98,12 +98,17 @@ readExpr input = case parse parseExpr "lisp" input of
 
 showVal :: LispVal -> String
 showVal (Atom atom)   = atom
+showVal (List list)   = "(" ++ unwordsList list ++ ")"
+showVal (DottedList head tail)   = "(" ++ unwordsList head ++ " . " ++ showVal tail ++ ")"
 showVal (Number n)    = show n
 showVal (String str)  = "\"" ++ str ++ "\""
 showVal (Character c) = "'" ++ [c] ++ "'"
 showVal (Bool True)   = "#t"
 showVal (Bool False)  = "#f"
 
+unwordsList :: [LispVal] -> String
+unwordsList = unwords . map showVal
+
 main :: IO ()
 main = do
     args <- getLine