Re: [PATCH for Dlang support 1/2] d: create the Parser.Context class

[Adela Vais]

Hello,

Thank you for the explanations, H.S.! I followed your suggestion.

I modified as requested.

>From 269f37d3d2f5d449e6530c825d26a7c3a9a8a38c Mon Sep 17 00:00:00 2001
From: Adela Vais <adela.vais@yahoo.com>
Date: Sun, 1 Nov 2020 22:13:42 +0200
Subject: [PATCH for Dlang support 1/2] d: fix Context class

All methods are now declared as const. Method getExpectedTokens() has now
the
functionality of reporting only the number of expected tokens.

* data/skeletons/lalr1.d: Fix Context class.
---
 data/skeletons/lalr1.d | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/data/skeletons/lalr1.d b/data/skeletons/lalr1.d
index 9b7c786c..4259473d 100644
--- a/data/skeletons/lalr1.d
+++ b/data/skeletons/lalr1.d
@@ -721,9 +721,9 @@ m4_popdef([b4_at_dollar])])dnl
   public static final class Context
   {

-    private YYStack yystack;
+    private const(YYStack) yystack;
     private SymbolKind yytoken;]b4_locations_if([[
-    private ]b4_location_type[ yylocation;]])[
+    private const(]b4_location_type[) yylocation;]])[

     this(YYStack stack, SymbolKind kind]b4_locations_if([[,
]b4_location_type[ loc]])[)
     {
@@ -737,7 +737,7 @@ m4_popdef([b4_at_dollar])])dnl
       return yytoken;
     }]b4_locations_if([[

-    final ]b4_location_type[ getLocation()
+    final const(]b4_location_type[) getLocation() const
     {
       return yylocation;
     }]])[
@@ -747,12 +747,12 @@ m4_popdef([b4_at_dollar])])dnl
      * YYARG is null, return the number of expected tokens (guaranteed to
      * be less than YYNTOKENS).
      */
-    int getExpectedTokens(SymbolKind[] yyarg, int yyargn)
+    int getExpectedTokens(SymbolKind[] yyarg, int yyargn) const
     {
       return getExpectedTokens(yyarg, 0, yyargn);
     }

-    int getExpectedTokens(SymbolKind[] yyarg, int yyoffset, int yyargn)
+    int getExpectedTokens(SymbolKind[] yyarg, int yyoffset, int yyargn)
const
     {
       int yycount = yyoffset;
       int yyn = yypact_[this.yystack.stateAt(0)];
@@ -769,16 +769,17 @@ m4_popdef([b4_at_dollar])])dnl
         for (int yyx = yyxbegin; yyx < yyxend; ++yyx)
           if (yycheck_[yyx + yyn] == yyx && yyx != ]b4_symbol(1, kind)[
               && !yyTableValueIsError(yytable_[yyx + yyn]))
-            yycount++;
-        if (yycount < yyargn)
-        {
-          yycount = 0;
-          for (int x = yyxbegin; x < yyxend; ++x)
-            if (yycheck_[x + yyn] == x && x != ]b4_symbol(1, kind)[
-                && !yyTableValueIsError(yytable_[x + yyn]))
-              yyarg[yycount++] = SymbolKind(x);
-        }
+          {
+            if (yyarg is null)
+              ++yycount;
+            else if (yycount == yyargn)
+              return 0;
+            else
+              yyarg[yycount++] = SymbolKind(yyx);
+          }
       }
+      if (yyarg !is null && yycount == yyoffset && yyoffset < yyargn)
+        yyarg[yyoffset] = ]b4_symbol(empty, kind)[;
       return yycount - yyoffset;
     }
   }
@@ -897,7 +898,7 @@ m4_popdef([b4_at_dollar])])dnl
       stack.length -= num;
     }

-    public final int stateAt (int i)
+    public final int stateAt (int i) const
     {
       return stack[$-i-1].state;
     }
-- 
2.17.1

În mie., 28 oct. 2020 la 07:43, Akim Demaille <akim@lrde.epita.fr> a scris:

> Hi H.S.,
>
> > Le 27 oct. 2020 à 17:55, H. S. Teoh <hsteoh@quickfur.ath.cx> a écrit :
> >
> > On Tue, Oct 27, 2020 at 07:38:46AM +0100, Akim Demaille wrote:
> > [...]
> >>> +  /**
> >>> +   * Information needed to get the list of expected tokens and to
> forge
> >>> +   * a syntax error diagnostic.
> >>> +   */
> >>> +  public static final class Context
> >>> +  {
> >>> +
> >>> +    private YYStack yystack;
> >>
> >> Is this a copy of the stack?  It does not look like a
> >> reference/pointer to the this.  We must not copy it, it's big, and
> >> readonly here.  It should be "const", but I don't know how that is
> >> spelled in D.
> > [...]
> >
> > Is YYStack a struct or class? Or an array? If it's an array or class,
> > it's a reference type by default.
>
> It's a struct.  But I guess it's not so bad as it contains only an
> array:
>
>   private final struct YYStack {
>     private YYStackElement[] stack = [];
>   ...
>
> so after all, it is not so big, I expect the inner array to be
> "copied" by reference.
>
>
> > W.r.t. const, there are several ways to spell it, depending on the
> > intended semantics.  If it should be an immutable reference, then you
> > could write it as:
> >
> >       private const(YYStack) yystack;
> >
> > In this case, the variable cannot be reassigned after initialization,
> > and if it's a reference type, it cannot be rebound.  Also, any elements
> > you retrieve from it will be const (const in D is transitive).
>
> I believe this is what we need here.
>
> > If it's an array, you can optionally have a mutable slice of immutable
> > elements (i.e., a view that can change, but the underlying elements are
> > not changeable):
> >
> >       private const(E)[] yystack;     // where E is the element type of
> YYStack
>
> Now I see why const takes parens.
>
> Thanks a lot for your explanations!
>