in reply to Pattern Matching, left-to-right

Tested successfully with the input you supplied:

Update

The last version did what I claimed but was still bad. Fair enough, thanks for spotting the problem Aristotle. The last version is behind the Read More .... The new version hopefully does what is wanted; here's my tests before and after changes:

Update 2

But that version was the same solution that others had :-(

Here's a third version that doesn't use regexes. TMTOWTDI! 

# hl7_conv

use strict;
use warnings;

my $input = q(AB\T\F\S\CD\E\E\E\R\R\R);
my $gen_out = '';
my $exp_out = q(AB&F^CD\\E\\R~R);

my %convs = (
    E   => '\\',
    F   => '|',
    R   => '~',
    S   => '^',
    T   => '&',
);

$gen_out = hl7_replace($input);

print "INPUT:   $input\n";
print "GEN_OUT: $gen_out\n";
print "EXP_OUT: $exp_out\n";

print $0, ': ', $gen_out eq $exp_out ? 'SUCCESS!' : '  Z z . c8o,  ', 
+"\n";

exit 0;

sub hl7_replace
{
    my $in = shift;

    my @input = split //, $in;
    my @output = ();

    for (my $i = 0; $i <= $#input; ++$i)
    {
        if ($input[$i] eq "\\" && ($i + 2) <= $#input 
            && $convs{$input[$i + 1]} && $input[$i + 2] eq "\\")
        {
            push @output, $convs{$input[$i + 1]};
            $i += 2;
        }
        else
        {
            push @output, $input[$i];
        }
    }

    return join '', @output;
}

[download]

Second Version Follows:

[ ~/tmp ] $ perl hl7_conv 
INPUT:   AB\T\F\S\CD\E\E\E\R\R\R
GEN_OUT: AB&F^CD\E\E~R\R
EXP_OUT: AB&F^CD\E\R~R
hl7_conv:   Z z . c8o,  
[ ~/tmp ] $ perl hl7_conv 
INPUT:   AB\T\F\S\CD\E\E\E\R\R\R
GEN_OUT: AB&F^CD\E\R~R
EXP_OUT: AB&F^CD\E\R~R
hl7_conv: SUCCESS!

[download]

Here's the new code: 

# hl7_conv

use strict;
use warnings;

my $input = q(AB\T\F\S\CD\E\E\E\R\R\R);
my $gen_out = '';
my $exp_out = q(AB&F^CD\\E\\R~R);

my $rx_hl7_ctrl_chars = qr/\\([EFRST])\\/;
my %convs = (
    E   => '\\',
    F   => '|',
    R   => '~',
    S   => '^',
    T   => '&',
);

$gen_out = hl7_replace($input);

print "INPUT:   $input\n";
print "GEN_OUT: $gen_out\n";
print "EXP_OUT: $exp_out\n";

print $0, ': ', $gen_out eq $exp_out ? 'SUCCESS!' : '  Z z . c8o,  ', 
+"\n";

exit 0;

sub hl7_replace
{
    my $in = shift;

    $in =~ s/$rx_hl7_ctrl_chars/$convs{$1}/g;

    return $in;
}

[download]

Old Version Follows: 

# hl7_conv

use strict;
use warnings;

my $input = q(AB\T\F\S\CD);
my $gen_out = '';
my $exp_out = q(AB&F^CD);

my %convs = (
    '|'     => qr/\\F\\/,
    '^'     => qr/\\S\\/,
    '&'     => qr/\\T\\/,
    '~'     => qr/\\R\\/,
    '\\'    => qr/\\E\\/,
);

$gen_out = hl7_replace($input);

print "INPUT:   $input\n";
print "GEN_OUT: $gen_out\n";
print "EXP_OUT: $exp_out\n";

print $0, ': ', $gen_out eq $exp_out ? 'SUCCESS!' : '  Z z . c8o,  ', 
+"\n";

exit 0;

sub hl7_replace
{
    my $in = shift;

    foreach my $key (keys %convs)
    {
        $in =~ s/$convs{$key}/$key/g;
    }

    return $in;
}

[download]

Here's the output: 

[ ~/tmp ] $ perl hl7_conv 
INPUT:   AB\T\F\S\CD
GEN_OUT: AB&F^CD
EXP_OUT: AB&F^CD
hl7_conv: SUCCESS!
[ ~/tmp ] $

[download]

Regards,

PN5

Replies are listed 'Best First'.
Re^2: Pattern Matching, left-to-right
by Aristotle (Chancellor) on Aug 21, 2004 at 14:11 UTC

    If you had tested it with more input, you'd have found it is wrong.

    You wrote:

        foreach my $key (keys %convs)
    {
        $in =~ s/$convs{$key}/$key/g;
    }

    [download]

    The OP wrote:

    And that *almost* works perfectly. Where it doesn't work is if there's two of these special characters grouped around a normal character... [...] And since I can get these in any order, there's no way to put them in an order that always works.

    Since you stored the patterns as values in a hash, the order in which they're substituted gets randomized such that with the input you tested with, the code happens to work.

    Makeshifts last the longest.

[reply]
[d/l]

      Thanks - fixed - see update.

      Regards,

      PN5

[reply]

        Of course, that's exactly the same as the solutions by antirice and by ysth.. :-)

        Makeshifts last the longest.

[reply]

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