git.iko.soy/elk
on 06503fe help sign in
elk/compiler/SourceSyntax/Pattern.hs
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1module SourceSyntax.Pattern where
3import Data.List (intercalate)
4import SourceSyntax.Helpers as Help
5import SourceSyntax.PrettyPrint
6import Text.PrettyPrint as PP
7import qualified Data.Set as Set
8import SourceSyntax.Literal as Literal
10data Pattern = PData String [Pattern]
11 | PRecord [String]
12 | PAlias String Pattern
13 | PVar String
14 | PAnything
15 | PLiteral Literal.Literal
16 deriving (Eq, Ord, Show)
18cons h t = PData "::" [h,t]
19nil = PData "[]" []
20list = foldr cons nil
21tuple es = PData ("_Tuple" ++ show (length es)) es
23boundVars :: Pattern -> Set.Set String
24boundVars pattern =
25 case pattern of
26 PVar x -> Set.singleton x
27 PAlias x p -> Set.insert x (boundVars p)
28 PData _ ps -> Set.unions (map boundVars ps)
29 PRecord fields -> Set.fromList fields
30 PAnything -> Set.empty
31 PLiteral _ -> Set.empty
34instance Pretty Pattern where
35 pretty pattern =
36 case pattern of
37 PVar x -> variable x
38 PLiteral lit -> pretty lit
39 PRecord fs -> PP.braces (commaCat $ map variable fs)
40 PAlias x p -> prettyParens p <+> PP.text "as" <+> variable x
41 PAnything -> PP.text "_"
42 PData "::" [hd,tl] -> parensIf isCons (pretty hd) <+> PP.text "::" <+> pretty tl
43 where isCons = case hd of
44 PData "::" _ -> True
45 _ -> False
46 PData name ps ->
47 if isTuple name then
48 PP.parens . commaCat $ map pretty ps
49 else hsep (PP.text name : map prettyParens ps)
51prettyParens pattern = parensIf needsThem (pretty pattern)
52 where
53 needsThem =
54 case pattern of
55 PData name (_:_) | not (isTuple name) -> True
56 PAlias _ _ -> True
57 _ -> False