#!/usr/bin/perl

use strict;
use warnings FATAL => 'all';
use Data::Dumper;
use Term::ReadLine;
use HTML::Template::Expr;

my %data = (
   a => 5,
   b => 1,
   c => 7,
   d => 100,
);

my $term = Term::ReadLine->new('foo');

my $expr;
while (1) {
   $expr = $term->readline('Enter expression: ');
   my $tmpl = compile($expr,[keys %data]);
   $tmpl->param(\%data);
   print Dumper ($tmpl->output);
}


sub compile {
  my $expr = shift;
  my $known_cols = shift;

  my $tmpl_expr = "";
  $tmpl_expr .= sprintf ('<TMPL_VAR expr="%s">', $expr);
  #
  # 'declare' known 'columns'
  #
  $tmpl_expr .= join('', map {sprintf('<TMPL_IF "%s"></TMPL_IF>',$_)} @$known_cols);
  warn("expr=$tmpl_expr");

  return HTML::Template::Expr->new(
				   die_on_bad_params => 1,
				   scalarref => \$tmpl_expr);
}