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package PosExpr;
# automatically generated implementation of recursive data type
# PosExpr = I(int n)
# or N(string name)
# or NO(string name,char op,int n)
use strict;
use warnings;
use feature 'say';
use overload '""' => \&as_string;
use overload 'eq' => \&streq;
# PosExpr->I: Constructor or get method, use:
# my $obj = PosExpr->I($n) OR
# my $n = $obj->I
sub I ($;$)
{
my( $thing, $n ) = @_;
if( @_ == 2 ) # constructor
{
die "PosExpr->I: classname $thing is not 'PosExpr'\n"
unless $thing eq "PosExpr";
return bless ["I", $n], "PosExpr";
} else # get method
{
die "PosExpr->I: $thing is not a PosExpr\n"
unless ref($thing) eq "PosExpr";
my @x = @$thing;
my $t = shift @x;
die "PosExpr->I: malformed object $thing\n"
unless @x == 1 && $t eq "I";
return $x[0];
}
}
# PosExpr->N: Constructor or get method, use:
# my $obj = PosExpr->N($name) OR
# my $name = $obj->N
sub N ($;$)
{
my( $thing, $name ) = @_;
if( @_ == 2 ) # constructor
{
die "PosExpr->N: classname $thing is not 'PosExpr'\n"
unless $thing eq "PosExpr";
return bless ["N", $name], "PosExpr";
} else # get method
{
die "PosExpr->N: $thing is not a PosExpr\n"
unless ref($thing) eq "PosExpr";
my @x = @$thing;
my $t = shift @x;
die "PosExpr->N: malformed object $thing\n"
unless @x == 1 && $t eq "N";
return $x[0];
}
}
# PosExpr->NO: Constructor or get method, use:
# my $obj = PosExpr->NO($name, $op, $n) OR
# my ($name, $op, $n) = $obj->NO
sub NO ($;$$$)
{
my( $thing, $name, $op, $n ) = @_;
if( @_ == 4 ) # constructor
{
die "PosExpr->NO: classname $thing is not 'PosExpr'\n"
unless $thing eq "PosExpr";
return bless ["NO", $name, $op, $n], "PosExpr";
} else # get method
{
die "PosExpr->NO: $thing is not a PosExpr\n"
unless ref($thing) eq "PosExpr";
my @x = @$thing;
my $t = shift @x;
die "PosExpr->NO: malformed object $thing\n"
unless @x == 3 && $t eq "NO";
return @x;
}
}
sub kind ($)
{
my( $self ) = @_;
die "PosExpr->kind: $self is not a PosExpr\n"
unless ref($self) eq "PosExpr";
return $self->[0];
}
sub as_string ($)
{
my( $self ) = @_;
die "PosExpr->as_string: $self is not a PosExpr\n"
unless ref($self) eq "PosExpr";
my @x = @$self;
my $t = shift @x;
# stringify all params
@x = map { "$_" } @x;
# specific printing rules
return "$x[0]" if $t eq 'I';
return "$x[0]" if $t eq 'N';
return "$x[0]$x[1]$x[2]" if $t eq 'NO';
# general case
my $args = join( ',', @x );
return $args ne "" ? "$t($args)" : "$t";
}
sub streq ($$)
{
my( $a, $b ) = @_;
#print "PosExpr->streq called with a=$a, b=$b\n";
return "$a" eq "$b" ? 1 : 0; # the sneaky way
}
use Data::Dumper;
my $debug = 0;
sub setdebug { my($d) = @_; $debug = $d; }
#
# my($pe,$leftover) = parse($input);
# Parse $input, a string starting with a position expression,
# delivering the position expression in $pe and the leftover
# input in $leftover. Die screaming if no well formed pos expr
# can be found at the start of $input.
# A position expression is either \d+ or name or name '+'|'-' \d+
# The internal form of a posexpr is ['I', int const] or ['N', name]
# or ['NO', name, +-, offset]
#
sub parse ($)
{
my( $input ) = @_;
if( $input =~ s/^(\d+)\s*// )
{
return ( PosExpr->I($1), $input );
}
$input =~ s/^(\w+)\s*// ||
die "bad input in pos expr $input, name expected\n";
my $name = $1;
if( $input =~ s/^([\+-])\s*(\d+)\s*// )
{
if( $2 == 0 )
{
return ( PosExpr->N($name), $input );
} else
{
return ( PosExpr->NO($name,$1,$2), $input );
}
}
return ( PosExpr->N($name), $input );
}
#
# my $pe = simpleparse($str);
# Parse a position expression out of $str. Fail if there's
# anything left over.
#
sub simpleparse ($)
{
my( $str ) = @_;
my($pe,$leftover) = parse($str);
die "PosExpr->simpleparse($str): left over $leftover after pe $pe\n"
if $leftover;
return $pe;
}
#
# my $newpe = $pe->add($n);
# Arithmetic on PosExprs: add $n (an integer)
# to $pe, giving $newpe.
#
sub add
{
my( $self, $n ) = @_;
return $self if $n==0;
if( $self->kind eq 'I' )
{
my $x = $self->I;
return PosExpr->I( $x+$n );
} elsif( $self->kind eq "N" )
{
my $name = $self->N;
my $op = $n>0?'+':'-';
$n = abs($n);
return PosExpr->NO( $name, $op, $n );
} else
{
# .. NO( string name, char op, int n )
my( $name, $op, $x ) = $self->NO;
$x = -$x if $op eq '-';
$op = '+';
$x += $n;
return PosExpr->N( $name ) if $x==0;
$op = '-' if $x<0;
$x = abs($x);
return PosExpr->NO( $name, $op, $x );
}
}
#
# my $pos = $pe->eval($poshash);
# Evaluate the given PosExpr $pe, using %$poshash
# for name lookup. Returns the actual position (a number).
#
sub eval ($$)
{
my( $self, $poshash ) = @_;
if( $self->kind eq 'I' )
{
return $self->I;
} elsif( $self->kind eq 'N' )
{
my $name = $self->N;
die "error in PosExpr::eval($self): ".
"no such name $name in poshash ". Dumper($poshash)
unless exists $poshash->{$name};
return $poshash->{$name};
} else # if( $self->kind eq 'NO' )
{
my ($name, $op, $n) = $self->NO;
die "error in PosExpr::eval($self): ".
"no such name $name in poshash ". Dumper($poshash)
unless exists $poshash->{$name};
die "error in PosExpr::eval($self): bad op $op\n" unless
$op eq '+' || $op eq '-';
$n = - $n if $op eq '-';
return $poshash->{$name} + $n;
}
}
1;
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