From martin@mathematik.uni-ulm.de

I wonder why perl stumbles over string literals in certain map
contexts, so that, e.g.​:

  @​x = map { '', 1 } @​y;

is considered a syntax error, whereas​:

  @​x = map { 1, '' } @​y;

works just fine. I observed this behaviour with versions 5.000
through 5.00503.

Site configuration information for perl 5.00503​:

Configured by borchert at Fri Aug 13 13​:49​:21 MET DST 1999.

Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration​:
  Platform​:
  osname=solaris, osvers=2.5.1, archname=sun4-solaris
  uname='sunos turing 5.5.1 generic_103640-23 sun4u sparc sunw,ultra-enterprise '
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef useperlio=undef d_sfio=undef
  Compiler​:
  cc='cc', optimize='-O', gccversion=
  cppflags='-I/usr/local/include'
  ccflags ='-I/usr/local/include'
  stdchar='unsigned char', d_stdstdio=define, usevfork=false
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  alignbytes=8, usemymalloc=y, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib /usr/ccs/lib
  libs=-lsocket -lnsl -lgdbm -ldl -lm -lc -lcrypt
  libc=/lib/libc.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags=' '
  cccdlflags='-KPIC', lddlflags='-G -L/usr/local/lib'

Locally applied patches​:
 

@​INC for perl 5.00503​:
  /usr/local/perl5.005_03/lib/5.00503/sun4-solaris
  /usr/local/perl5.005_03/lib/5.00503
  /usr/local/perl5.005_03/lib/site_perl/5.005/sun4-solaris
  /usr/local/perl5.005_03/lib/site_perl/5.005
  .

Environment for perl 5.00503​:
  HOME=/home/turing/martin
  LANG (unset)
  LANGUAGE (unset)
  LD_LIBRARY_PATH=/usr/openwin/lib​:/usr/local/lib/x11
  LOGDIR (unset)
  PATH=​:/home/turing/martin/bin​:/usr/local/games​:/usr/games​:/usr/local/bin​:/usr/openwin/bin​:/usr/openwin/bin/xview​:/opt/X11R5/bin​:/usr/openwin/demo​:/usr/bin​:/usr/ccs/bin​:/usr/ucb​:/home/turing/martin/wonders/dq/bin
  PERL_BADLANG (unset)
  SHELL=ksh

From @tamias

On Tue, Sep 07, 1999 at 03​:10​:58PM +0200, Martin Hasch wrote​:

I wonder why perl stumbles over string literals in certain map
contexts, so that, e.g.​:

@​x = map \{ ''\, 1 \} @​y;

is considered a syntax error, whereas​:

@​x = map \{ 1\, '' \} @​y;

works just fine. I observed this behaviour with versions 5.000
through 5.00503.

Because perl doesn't know whether the { } is a block or an anonymous hash
constructor. If the contents of { } begin with a string literal followed by
a comma, perl assumes that it is an anonymous hash constructor; otherwise,
perl assumes it is a block. Sometimes the programmer needs to disambiguate
the code to keep perl from guessing incorrectly.

Ronald