From pbdb_test@rfi.net

For some reason, Perl accepts a while loop with an empty conditional.
  while ( ) { print "TRUE"; sleep 1; }
results in a big list of TRUEs. This is odd in several ways​:

  1) Everything else (until, if, unless...) is a syntax error with an
  empty condition.
  2) The empty condition of a while loop is TRUE! If anything I would
  expect false.
  3) There's no warning.

At minimum there should be a warning, at best it should be made a
syntax error.

This looks like a documentation problem.

Here's another intersting problem​:

do { print "TRUE"; sleep 1 } while ();
This produces one iteration of TRUE.

do { print "TRUE"; sleep 1 } until ();
This produces an infinite loop.

Again, the oddness​:
  1) Unlike with while () {...}, the null condition is false!
  2) Again, no warning.

IMHO do {...} while () and do {...} until () should both be syntax
errors, or at least warnings.

Unless there's a backwards compatibility issue, all instances of an
empty conditional should probably be a syntax error. I can't think of
any time when it would be useful.

If I'm feeling brave I'll submit a patch.

PS This problem occurs under 5.005_03 and 5.005_62

Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration​:
  Platform​:
  osname=macOS, osvers=2.2.7, archname=i686-linux
  uname='linux athens 2.2.7 #2 smp mon may 10 23​:17​:01 edt 1999 i686 unknown '
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef useperlio=undef d_sfio=undef
  Compiler​:
  cc='gcc', optimize='-O6', gccversion=egcs-2.91.66 19990314 (egcs-1.1.2 release)
  cppflags='-Dbool=char -DHAS_BOOL -I/usr/local/include'
  ccflags ='-Dbool=char -DHAS_BOOL -I/usr/local/include'
  stdchar='char', d_stdstdio=undef, usevfork=false
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  alignbytes=4, usemymalloc=y, prototype=define
  Linker and Libraries​:
  ld='gcc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib
  libs=-lnsl -lndbm -lgdbm -ldbm -ldb -ldl -lm -lc -lposix -lcrypt
  libc=, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
  cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Characteristics of this binary (from libperl)​:
  Built under linux
  Compiled at Jul 29 1999 00​:29​:00
  %ENV​:
  PERL5LIB="/home/schwern/lib/perl5/site_perl/5.005​:/web/sites/test/mp"
  @​INC​:
  /home/schwern/lib/perl5/site_perl/5.005/i686-linux
  /home/schwern/lib/perl5/site_perl/5.005
  /web/sites/test/mp
  /usr/lib/perl5/i686-linux
  /usr/lib/perl5
  /usr/lib/perl5/site_perl/5.005/i686-linux
  /usr/lib/perl5/site_perl/5.005
  .

Summary of my perl5 (revision 5.0 version 5 subversion 62) configuration​:
  Platform​:
  osname=linux, osvers=2.2.10, archname=i686-linux
  uname='linux athens 2.2.10 #3 smp mon aug 2 16​:48​:09 edt 1999 i686 unknown '
  config_args=''
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef useperlio=undef d_sfio=undef
  use64bits=undef usemultiplicity=undef
  Compiler​:
  cc='cc', optimize='-g', gccversion=2.95.2 19990906 (prerelease)
  cppflags='-Dbool=char -DHAS_BOOL -DDEBUGGING -I/usr/local/include -DDEBUGGING_OPS -DDEBUGGING_MSTATS -fno-strict-aliasing'
  ccflags ='-Dbool=char -DHAS_BOOL -DDEBUGGING -I/usr/local/include -DDEBUGGING_OPS -DDEBUGGING_MSTATS -fno-strict-aliasing'
  stdchar='char', d_stdstdio=define, usevfork=false
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  alignbytes=4, usemymalloc=y, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib
  libs=-lnsl -lndbm -lgdbm -ldbm -ldb -ldl -lm -lc -lposix -lcrypt
  libc=/lib/libc-2.1.2.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
  cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Characteristics of this binary (from libperl)​:
  Compile-time options​: DEBUGGING
  Built under linux
  Compiled at Oct 16 1999 16​:16​:24
  %ENV​:
  PERL5LIB="/home/schwern/lib/perl5/site_perl/5.005​:/web/sites/test/mp"
  @​INC​:
  /home/schwern/lib/perl5/site_perl/5.005/i686-linux
  /home/schwern/lib/perl5/site_perl/5.005
  /web/sites/test/mp
  /usr/local/perl5.005_62/lib/5.00562/i686-linux
  /usr/local/perl5.005_62/lib/5.00562
  /usr/local/perl5.005_62/lib/site_perl/5.00562/i686-linux
  /usr/local/perl5.005_62/lib/site_perl
  .

--

Michael G Schwern schwern@​pobox.com
  http​://www.pobox.com/~schwern
  /(?​:(?​:(1)[.-]?)?\(?(\d{3})\)?[.-]?)?(\d{3})[.-]?(\d{4})(x\d+)?/i