[tex-k] [WEB] Refactor 'reduce/red' and 'squash/sq'

[Andreas Scherer]

Dear all,

Leaning on a similar change in CWEB 4.6 (t.b.a.), I've created the 
attached change file 'squash.ch' against 'weave.web'. It refactors the 
special case 'squash(..,1,..)', which did _not_ apply 'app1()' before 
'red(..,1,..)', but was, in fact, a super-compact variant of 'red()'.

All instances of 'squash(..,1,..)' are now 'reduce(..,0,..)'.

Curiously enough, there is no 'squash(..,1,..)' in WEAVE, but CWEAVE has 
two rules that merged the former squence 'app1(); reduce(..,1,..)' into 
the new 'squash(..,1,..)'.

Apply 'squash.ch' with
$> tie -c weave-squash.ch weave.web [weave.ch] squash.ch
and use 'weave-squash.ch' instead of 'weave.ch' when tangling and 
weaving WEAVE.

Stay safe!
Andreas
-------------- next part --------------
Changes for WEAVE.WEB to clean up 'reduce/red' and 'squash/sq'.

The original 'squash(..,1,..)' was /not/ a combination of 'app1()' and
'reduce(..,1,..)'; instead, it was an ultra-compact variant of 'reduce'.

Moving the special case 'k==1' from 'sq' to 'red' as separate case 'k==0'
makes 'squash(..,k,..)' orthogonal in 'k=1,..,4'.  Curiously enough, now
there's no 'squash(..,1,..)' anymore, but CWEAVE has at least two rules
that apply this case.

Apply this extended change file with
$> tie -c weave-squash.ch weave.web weave.ch squash.ch
and use 'weave-squash.ch' instead of 'weave.ch' when tangling and weaving.

Public domain.  Originally written by Andreas Scherer, 2021.

@x
{\sl Caution:\/} The macros |app|, |app1|, |app2|, and |app3| are
@y
{\sl Caution:\/} The macros |app|, |app1|, |app2|, |app3|, and |app4| are
@z

@x
@d app3(#)==app2(#);app1(#+2)
@y
@d app3(#)==app2(#);app1(#+2)
@d app4(#)==app3(#);app1(#+3)
@z
 
@x
else if cat[pp+1]=simp then squash(pp+1,1,math,0)(4)
@y
else if cat[pp+1]=simp then
  begin reduce(pp+1,0,math,0)(4);
  end
@z
 
@x
squash(pp,1,intro,-3)(14)
@y
begin reduce(pp,0,intro,-3)(14);
end
@z

@x
else squash(pp,1,simp,-2)(25)
@y
else
  begin reduce(pp,0,simp,-2)(25);
  end
@z
 
@x
else if cat[pp+1]=simp then squash(pp+1,1,math,0)(35)
@y
else if cat[pp+1]=simp then
  begin reduce(pp+1,0,math,0)(35);
  end
@z

@x
squash(pp,1,terminator,-3)(42)
@y
begin reduce(pp,0,terminator,-3)(42);
end
@z
 
@x
if cat[pp+1]=close then squash(pp,1,stmt,-2)(43)
@y
if cat[pp+1]=close then
  begin reduce(pp,0,stmt,-2)(43);
  end
@z

@x
  begin app(force); app(backup); app2(pp); reduce(pp,2,intro,-3)(44);
@y
  begin app(force); app(backup); squash(pp,2,intro,-3)(44);
@z

@x
squash(pp,1,stmt,-2)(50)
@y
begin reduce(pp,0,stmt,-2)(50);
end
@z
 
@x
if cat[pp+1]=beginning then squash(pp,1,stmt,-2)(51)
@y
if cat[pp+1]=beginning then
  begin reduce(pp,0,stmt,-2)(51);
  end
@z

@x
scrap list.
@y
scrap list.  This procedure takes advantage of the simplification that
occurs when |k=0|.
@z
 
@x
begin cat[j]:=c; trans[j]:=text_ptr; freeze_text;
@y
begin cat[j]:=c;
if k>0 then
  begin
    trans[j]:=text_ptr; freeze_text;
  end;
@z

@x
@ Similarly, the `|squash|' macro invokes a procedure called `|sq|'. This
procedure takes advantage of the simplification that occurs when |k=1|.
@y
@ Similarly, the `|squash|' macro invokes a procedure called `|sq|', which
combines |app|${}_k$ and |red| for matching numbers~|k|.
@z
 
@x
var i:0..max_scraps; {index into scrap memory}
begin if k=1 then
  begin cat[j]:=c; @<Change |pp|...@>;
  end
else  begin for i:=j to j+k-1 do
    begin app1(i);
    end;
  red(j,k,c,d);
  end;
@y
begin
  case k of
  1: begin app1(j);@+ end;
  2: begin app2(j);@+ end;
  3: begin app3(j);@+ end;
  4: begin app4(j);@+ end;
  othercases confusion('squash')
  endcases;@/
  red(j,k,c,d);
@z