git.iko.soy/elk
on e34245a help sign in
elk/compiler/SourceSyntax/Pattern.hs
46 lines 1.4 kB history raw
1module SourceSyntax.Pattern where
3import Data.List (intercalate)
4import SourceSyntax.Helpers as Help
5import SourceSyntax.PrettyPrint
6import Text.PrettyPrint as PP
7import SourceSyntax.Literal as Literal
9data Pattern = PData String [Pattern]
10 | PRecord [String]
11 | PAlias String Pattern
12 | PVar String
13 | PAnything
14 | PLiteral Literal.Literal
15 deriving (Eq, Ord, Show)
17cons h t = PData "::" [h,t]
18nil = PData "[]" []
19list = foldr cons nil
20tuple es = PData ("_Tuple" ++ show (length es)) es
23instance Pretty Pattern where
24 pretty pattern =
25 case pattern of
26 PVar x -> variable x
27 PLiteral lit -> pretty lit
28 PRecord fs -> PP.braces (commaCat $ map variable fs)
29 PAlias x p -> prettyParens p <+> PP.text "as" <+> variable x
30 PAnything -> PP.text "_"
31 PData "::" [hd,tl] -> parensIf isCons (pretty hd) <+> PP.text "::" <+> pretty tl
32 where isCons = case hd of
33 PData "::" _ -> True
34 _ -> False
35 PData name ps ->
36 if isTuple name then
37 PP.parens . commaCat $ map pretty ps
38 else sep (PP.text name : map prettyParens ps)
40prettyParens pattern = parensIf needsThem (pretty pattern)
41 where
42 needsThem =
43 case pattern of
44 PData name (_:_) | not (isTuple name) -> True
45 PAlias _ _ -> True
46 _ -> False