## Saturday, December 24, 2016

### The Twelve Days of Christmas

Programming Praxis posted a task to write a program to print the words to The Twelve Days of Christmas song. We are going to solve it in Factor.

We start off by defining all the gifts received on each day:

```CONSTANT: gifts {
{ "first" "a partridge in a pear tree" }
{ "second" "two turtle doves and " }
{ "third" "three French hens, " }
{ "fourth" "four calling birds, " }
{ "fifth" "five golden rings, " }
{ "sixth" "six geese a-laying, " }
{ "seventh" "seven swans a-swimming, " }
{ "eighth" "eight maids a-milking, " }
{ "ninth" "nine ladies dancing, " }
{ "tenth" "ten lords a-leaping, " }
{ "eleventh" "eleven pipers piping, " }
{ "twelfth" "twelve drummers drumming, " }
}```

Then we iterate through the days, gathering all the gifts in reverse for each day, and formatting them, and wrapping to 72 columns of text for display.

```gifts [
[ first ] [ 1 + gifts swap head values reverse concat ] bi*
"On the %s day of Christmas my true love gave to me %s." sprintf
72 wrap-string print nl
] each-index```

Which gives us these words:

On the first day of Christmas my true love gave to me a partridge in a pear tree.

On the second day of Christmas my true love gave to me two turtle doves and a partridge in a pear tree.

On the third day of Christmas my true love gave to me three French hens, two turtle doves and a partridge in a pear tree.

On the fourth day of Christmas my true love gave to me four calling birds, three French hens, two turtle doves and a partridge in a pear tree.

On the fifth day of Christmas my true love gave to me five golden rings, four calling birds, three French hens, two turtle doves and a partridge in a pear tree.

On the sixth day of Christmas my true love gave to me six geese a-laying, five golden rings, four calling birds, three French hens, two turtle doves and a partridge in a pear tree.

On the seventh day of Christmas my true love gave to me seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three French hens, two turtle doves and a partridge in a pear tree.

On the eighth day of Christmas my true love gave to me eight maids a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three French hens, two turtle doves and a partridge in a pear tree.

On the ninth day of Christmas my true love gave to me nine ladies dancing, eight maids a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three French hens, two turtle doves and a partridge in a pear tree.

On the tenth day of Christmas my true love gave to me ten lords a-leaping, nine ladies dancing, eight maids a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three French hens, two turtle doves and a partridge in a pear tree.

On the eleventh day of Christmas my true love gave to me eleven pipers piping, ten lords a-leaping, nine ladies dancing, eight maids a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three French hens, two turtle doves and a partridge in a pear tree.

On the twelfth day of Christmas my true love gave to me twelve drummers drumming, eleven pipers piping, ten lords a-leaping, nine ladies dancing, eight maids a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three French hens, two turtle doves and a partridge in a pear tree.