Add wildcard patterns

docs/language-reference.md

@@ -29,6 +29,14 @@ def answer
 
 Note that the above function will not work if it is called with any argument other than those three that it pattern matches on, because it lacks a catch-all pattern.
 
+You can use `_` to match any value and discard the result.
+
+```
+def answer
+    "hello" -> "hi"
+    _ -> "I don't understand"
+```
+
 Multi-argument functions are automatically curried, so they can be partially applied.
 
 ```

src/Language/Dtfpl/Parser.hs

@@ -66,9 +66,10 @@ defAlt = addLoc $ exprBlockMid $
 
 -- | Parse a pattern.
 pat :: PParsec p => p (A Pat 'Source)
-pat = varPat <|> litPat
+pat = varPat <|> litPat <|> wildPat
   where varPat = addLoc $ VarPat <$> ident
         litPat = addLoc $ LitPat <$> literal
+        wildPat = addLoc $ wildcard $> WildPat
 
 -- | Given a parser for some node constructor that takes an 'Expr' as argument,
 -- run that parser and run the 'expr' parser so that the continuation indent
@@ -181,11 +182,12 @@ symbol :: PParsec p => String -> p ()
 symbol = void . string
 
 -- | Symbol parser.
-arrow, comma, equals, lambda :: PParsec p => p ()
+arrow, comma, equals, lambda, wildcard :: PParsec p => p ()
 arrow = symbol "->"
 comma = symbol ","
 equals = symbol "="
 lambda = symbol "\\"
+wildcard = symbol "_"
 
 -- | Characters which cannot be used in identifiers.
 {-# ANN reservedChars "HLint: ignore Use String" #-}

src/Language/Dtfpl/Simplify/UnDef.hs

@@ -46,9 +46,6 @@ import           Language.Dtfpl.Syntax
 -- >     3, 4 -> b
 -- >     _, _ -> c
 --
--- (Note that this isn't actually valid source for now since wildcard patterns
--- aren't supported yet.)
---
 -- The first 'VarPat' in each column of the 'DefAlt's will be used as the lambda
 -- parameter name for that parameter. If there is no 'VarPat' in that column,
 -- a 'GenIdentPart' based on the name of the function will be used.