feat: can parse a simple λ-expression

1 files changed, 27 insertions, 4 deletions

diff --git a/lambda-calcul/haskell/src/Minilang/Lambda/Parser.hs b/lambda-calcul/haskell/src/Minilang/Lambda/Parser.hs
index da590ad..545536d 100644
--- a/lambda-calcul/haskell/src/Minilang/Lambda/Parser.hs
+++ b/lambda-calcul/haskell/src/Minilang/Lambda/Parser.hs
@@ -13,15 +13,38 @@ type Parser = Parsec Void Text
 data ParseError = ParseError Text
   deriving (Eq, Show)
 
-data AST = Sym Text
+data AST = Sym Text | Abs Text AST
   deriving (Eq, Show)
 
 parse :: Text -> Either ParseError AST
 parse =
-  first (ParseError . pack . errorBundlePretty) . Text.Megaparsec.parse symbol ""
+  first (ParseError . pack . errorBundlePretty) . Text.Megaparsec.parse ast ""
 
-symbol :: Parser AST
-symbol = Sym . pack <$> identifier
+ast :: Parser AST
+ast = try lambda <|> try sym
+
+lambda :: Parser AST
+lambda =
+  between
+    lpar
+    rpar
+    ( do
+        lexeme "lam"
+        binding <- pack <$> between lpar rpar identifier
+        Abs binding <$> ast
+    )
+
+lpar :: Parser Text
+lpar = symbol "("
+
+rpar :: Parser Text
+rpar = symbol ")"
+
+symbol :: Text -> Parser Text
+symbol = L.symbol spaceConsumer
+
+sym :: Parser AST
+sym = Sym . pack <$> identifier
 
 identifier :: Parser String
 identifier =