From 45aab75f5351e843430399030c27a13cd7edea2e Mon Sep 17 00:00:00 2001
From: NeilBrown <neil@brown.name>
Date: Wed, 10 Mar 2021 17:07:53 +1100
Subject: [PATCH] updates

---
 twod | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)

diff --git a/twod b/twod
index 4c9a44e..251f794 100644
--- a/twod
+++ b/twod
@@ -3577,3 +3577,122 @@ ifstatement -> ifhead iftail
 	| iftail
    casehead -> case expr block
 
+
+24feb
+ Hmmm.  awkwardness.
+ An ifpart can be  "if expr then simple ;"... no it cannot...
+ But the problem was that some forms for a head with an optional tail
+ must end EOL, other forms need not.
+ But the whole must end EOL.
+ 
+ So: do we put EOL at end of 'statement' or end of IfSuffix
+
+ Let's try assuming it is at the end of 'statement'
+ So IfSuffix can assume an EOL follows
+ So CondStatement can too
+ So an ifhead either 'may' or 'must' be followed by an EOL.
+ If may, it is followed by IfSuffix which is empty, or starts OptEOL
+ If must, it is followed by empty or
+ No.. this isn't working for me.
+
+ Let's try assuming that a CondStatement ends with an EOL.
+ So an IfSuffix must too.  and it cannot be just EOL
+ If an ifhead that must be followed by EOL, it is either EOL or EOL IfSuffix
+ If it may be, then EOL or IfSuffix
+
+
+ ForPart ThenPart SwitchPart are ALWAYS followed by something, so can end
+   EOL or not, as suits
+ WhilePart IfPart CasePart might be the last thing so each option must
+   end with a SuffixEOL which ends with EOL or SuffixOpt which might not
+
+ What do I want to do about 
+     : SimpleStatements
+
+ It is useful for
+       case value : statement
+ and maybe even
+       if cond : statement
+ though for the latter I can and use 'then'.
+ For 'else' I don't need the ':', but it wouldn't hurt.
+
+ Problem is: do I insist on a trailing newline or ';'
+ If I don't then
+      case foo: bar case bar: baz
+ would be legal, but hard to read, as would
+      if cond : stat1 else stat2
+ which is probbly error prone.
+
+ But do I want
+    switch expr
+       case val1: st1
+       case val2: st2
+       else: st3
+
+ That looks like an indented block, but is really indented lines.
+ So it is probably a mistake.
+ So allow switch expr : or ';' at the end
+
+ Whatever happens after "switch expr" must work after "while expr block"
+
+ So....
+   If first case is not indented, none of them may be
+   If first is: it happens in an IN/OUT block, so again all the same
+
+ Can I implement that?  Can I have IN after a non-terminal somehow?
+ When I see an IN, I could reduce as long as go_to_cnt == 0.
+ That might help after an OUT, but not after EXPR,,
+
+ Or: look at next symbol. If it can be shifted, we ignore the IN.
+ If not, we reduce and try to shift the IN again.
+
+ Also: need to mark IN as ignored when popped off during error recovery,
+ and maintain stack when discarding during error recovery
+
+26feb2021
+ Syntax for blocks?
+   { IN statements OUT }
+   { simplestatements }
+   : IN Statements OUT
+
+ but what about
+   : simplestatements NL    .... or ';'
+
+ In other contexts I have
+   for simple; statements; then simple ; statements ; while expr:
+
+ I currently require a ';' or newline before "then" or "while"
+ 
+ Interesting other cases are:
+
+    case expr : simplestatements
+    while expr : simplestatements
+
+ For 'if' I currently have "if expr then simplestatements"
+
+ Because of 'for' and 'then' I don't want to require ':' before simplestatements.
+ I could have
+     while expr do simplestatements
+ But what do I do for 'case' ???  I really want the ':' there.
+ So I should use it for 'if' and 'while'
+ 'for' could be followed immediately by IN, as could then and even if/while
+ So the ':' comes after an expression.
+ 
+27feb2021
+ Problems with the idea of only using : to come after an expression.
+ 1/ "else" looks wrong compared to Python, but may I can get used to that
+ 2/ with "for" it would be simple statements, with "while" it would be expr
+    if there was no indent.  Do I need different things to look different?
+   If statements always follow ':', the "for" and "then" always need a ':'
+     for: a=1; then: a = a+1; while a < 10:
+
+   In C there is no difference, but I want a difference..
+
+03mar2021
+ Arg... I'm not struggle with parsing concepts this time, I'm struggling with code.
+ I want to add an "EOL" symbol to the grammar as a special terminal.
+ It is like "NEWLINE", but handled a bit differently.
+
+ In parsergen it is just another terminal symbol, but it mustn't get added
+ to the "known" list.  Currently all terminals from TK_reserved are added
+ to "known".  Maybe if I give it a number that is after the virtual symbols
-- 
2.43.0