Allow relation symbols with parameters

Parameters must follow the relation symbol and be surrounded by braces, like so: `\rel{x}{y}{z}`.

This attempt is still brittle/broken in a few ways:
- It makes using braces in creative ways in mixfix notation ambiguous.
- It does not verify that the parameters are used in a consistent manner for each symbol. It essentially allows users to define  `a\MyRel b` and `a\MyRel{x} b` (and ones with even more parameters).
- It allows parameters for all relation symbols, even for those where it makes no sense in ordinary TeX markup, e.g. `a <{x} b`.

1 files changed, 10 insertions, 5 deletions

diff --git a/source/Syntax/Adapt.hs b/source/Syntax/Adapt.hs
index b338d47..1b5a237 100644
--- a/source/Syntax/Adapt.hs
+++ b/source/Syntax/Adapt.hs
@@ -124,7 +124,7 @@ head = ScanNoun <$> noun
     <|> ScanAdj <$> adj
     <|> ScanVerb <$> verb
     <|> ScanFun <$> fun
-    <|> ScanRelationSymbol <$> relationSymbol
+    <|> ScanRelationSymbol . fst <$> relationSymbol
     <|> ScanFunctionSymbol <$> functionSymbol
     <|> ScanPrefixPredicate <$> prefixPredicate
 
@@ -184,14 +184,19 @@ verb = toLexicalPhrase <$> (var *> pat <* iff)
 fun :: RE Token LexicalPhrase
 fun = toLexicalPhrase <$> (the *> pat <* (is <|> comma))
 
-relationSymbol :: RE Token RelationSymbol
-relationSymbol = math relator' <* iff
+relationSymbol :: RE Token (RelationSymbol, Int)
+relationSymbol = definiendum <* iff
     where
-        relator' = do
+        definiendum = math do
             varSymbol
             rel <- symbol
+            k <- params
             varSymbol
-            pure rel
+            pure (rel, k)
+        params :: RE Token Int
+        params = do
+            vars <- many (sym InvisibleBraceL *> var <* sym InvisibleBraceR)
+            pure (length vars)
 
 functionSymbol :: RE Token FunctionSymbol
 functionSymbol = do