EulerLisp

Code Samples

(~>
  (range~ 1 1000)
  (select~ &(or (divides? 3 &1) (divides? 5 &1)))
  sum~
  (println "Solution: "))

Special Syntax

1. fst/rst instead of car/cdr, incl. chained versions ffst, ... (cadr)
2. ~> pipeline operator, (~> 1 (+ 2) (* 3) = (* 3 (+ 2 1))
3. lambda shorthand, &(+ &1 (* &2 2)) = (fn (a b) (+ a (* b 2)))
4. streams (lazy iterators), range~, map~, select~, ...

Advanced Data Structures

Note: Some of these could (and should) be implemented in the target language at some later time.

Priority Queues

• (make-priority-queue pairs), create a (max-)priority queue from a list of (element, priority) pairs
• (make-min-priority-queue pairs), create a (min-)priority queue from a list of (element, priority) pairs
• (priority-queue-insert! pq element priority), insert a new element
• (priority-queue-max pq), get the (element, priority) pair with the highest (or lowest, if the queue is a min-priority queue) priorty
• (priority-queue-pop! pq), same as priority-queue-max, but removes the element

>> (def pq (make-priority-queue (list (cons "foo" 1) (cons "bar" 5) (cons "baz" 7))))
>> (priority-queue-insert! pq "qux" 20)
>> (priority-queue-max pq)
=> ("qux" . 20)
>> (priority-queue-pop! pq)
=> ("qux" . 20)
>> (priority-queue-pop! pq)
=> ("baz" . 7)
>> (priority-queue-pop! pq)
=> ("bar" . 5)
>> (priority-queue-pop! pq)
=> ("foo" . 1)

Favourite Problems

• 169, The different ways a number can be expressed as sum of powers of 2
• 351, Hexagonal orchards

References

Background

• The Roots of Lisp

Algorithms & Data Structures

• The Art of Computer Programming
• Introduction to Algorithms

Implementation

• Lisp In Small Pieces

Specs

• R5RS
• R6RS
• R7RS
• The Scheme Programming Language