Add some comments on the alternative layout rule state

diff --git a/compiler/parser/Lexer.x b/compiler/parser/Lexer.x
index c78f3b9..cae5349 100644 (file)
--- a/compiler/parser/Lexer.x
+++ b/compiler/parser/Lexer.x
@@ -1499,10 +1499,19 @@ data PState = PState {
        context    :: [LayoutContext],
        lex_state  :: [Int],
         -- Used in the alternative layout rule:
        context    :: [LayoutContext],
        lex_state  :: [Int],
         -- Used in the alternative layout rule:

+        -- These tokens are the next ones to be sent out. They are
+        -- just blindly emitted, without the rule looking at them again:

         alr_pending_implicit_tokens :: [Located Token],
         alr_pending_implicit_tokens :: [Located Token],

+        -- This is the next token to be considered or, if it is Nothing,
+        -- we need to get the next token from the input stream:

         alr_next_token :: Maybe (Located Token),
         alr_next_token :: Maybe (Located Token),

+        -- This is what we consider to be the locatino of the last token
+        -- emitted:

         alr_last_loc :: SrcSpan,
         alr_last_loc :: SrcSpan,

+        -- The stack of layout contexts:

         alr_context :: [ALRContext],
         alr_context :: [ALRContext],

+        -- Are we expecting a '{'? If it's Just, then the ALRLayout tells
+        -- us what sort of layout the '{' will open:

         alr_expecting_ocurly :: Maybe ALRLayout
      }
        -- last_loc and last_len are used when generating error messages,
         alr_expecting_ocurly :: Maybe ALRLayout
      }
        -- last_loc and last_len are used when generating error messages,