Scheme is a functional programming language in the Lisp family, closely modeled on lambda calculus with eager (applicative-order) evaluation.
16
votes
1answer
242 views
Is this IRC bot utility library Racket-y enough?
To help myself learn Racket, I ported a simple JavaScript ircbot module I wrote for Node.js to Racket. The Racket version is built atop the Racket irc package, so ...
10
votes
1answer
403 views
On Implementing a Lisp
Background:
This began with James Colgan's Lisp-Dojo for Ruby. My implementation can be found here. I then moved on to Write yourself a scheme in 48 hours. This question has to do with one of the ...
9
votes
1answer
207 views
WebSocket-based API library in Racket
I've developed a library in (typed) Racket that wraps a WebSocket-based API. The API itself is very simple—it operates via a series of three-letter commands optionally followed by a JSON-encoded ...
8
votes
0answers
778 views
7
votes
2answers
382 views
My first accumulators
Notes
I'm working my way through SICP, and as I got very confused by the section on folds, I decided to try to implement foldr in scheme and javascript to understand how it works differently with ...
7
votes
3answers
834 views
Find all distinct triples less than N that sum to S
Exercise 2.41. Write a procedure to
find all ordered triples of distinct
positive integers i, j, and k less
than or equal to a given integer n
that sum to a given integer s.
...
7
votes
2answers
164 views
Write a procedure stream-limit that finds
From SICP:
Exercise 3.64. Write a procedure
stream-limit that takes as arguments a
stream and a number (the tolerance).
It should examine the stream until it
finds two successive elements ...
6
votes
4answers
297 views
Project Euler 1 (sum of multiples of 3 or 5 under 1000)
I solved this a while ago. In the moment I solved it I was learning Scheme and, well, I still am. I'm not looking at the best solution (I searched for it and coded it already, in Python), what I want ...
6
votes
1answer
3k views
Sum of squares of two largest of three numbers
Given the following problem (SICP Exercise 1.3):
Define a procedure that takes three
numbers as arguments and returns the
sum of squares of the two largest
numbers.
I wrote the following ...
6
votes
1answer
419 views
Improving a priority queue sketch in Racket/Scheme
I just put together the skeletons for a priority queue using a binary heap in racket/scheme. Using racket/scheme is all about the educational experience and I was wondering if anyone wants to ...
6
votes
1answer
56 views
Fisher-Yates shuffle in Scheme
There are many ways to shuffle lists; for example, Racket's built-in shuffle assigns each list element with a random number as a sort key, then sorts the list, ...
6
votes
1answer
72 views
Simon Says in Scheme
Ok, it's not completely like Simon Says, since it's text-based. There is nothing about memorizing based on visual cues and/or sound here, just memorizing long sequences of numbers. I wanted to do it ...
5
votes
2answers
4k views
Sorting a list of numbers in increasing order
Here's a program I wrote to sort a list of numbers in increasing order (without using inbuilt sort function).
...
5
votes
2answers
2k views
Cube root (Newton's method)
Newton's method for finding cube roots states that for any given \$x\$ and a guess \$y\$, a better approximation is \$\dfrac{(\dfrac{x}{y^2} + 2y)}{3}\$.
What do you think of this code for finding a ...
5
votes
1answer
439 views
Find the Hardy–Ramanujan number using R5RS scheme. Please suggest improvements in idiom and calculations.
I remember once going to see
[Srinivasa Ramanujan] when he was ill
at Putney. I had ridden in taxi cab
number 1729 and remarked that the
number seemed to me rather a dull one,
and that I ...
5
votes
1answer
107 views
Simple evaluator of Scheme-like expressions in Haskell
This is my first nontrivial Haskell program:
...
5
votes
2answers
644 views
Insert-everywhere function
This is HtDP Excercise 12.4.2:
Develop a function insert-everywhere. It consumes a symbol and a list
of words. The result is a list of words like its second argument, but
with the first ...
4
votes
1answer
435 views
Code from “Write Yourself a Scheme in 48 Hours” tutorial
I recently went through this Haskell tutorial.
I'd be interested in any thoughts or comments at all, in terms of improving the structure, order, haskell conventions, or that long, kind of ugly eval ...
4
votes
2answers
298 views
Why is this RC4 code in Racket so slow?
According to shootout.alioth.debian.org, Racket is not much slower than C#, at least in the same order of magnitude due to its JIT compiler.
However, I'm seeing at least two degrees of magnitude ...
4
votes
1answer
178 views
Set representation allowing duplicates
From SICP:
Exercise 2.60. We specified that a
set would be represented as a list
with no duplicates. Now suppose we
allow duplicates. For instance, the
set {1,2,3} could be represented as
...
4
votes
1answer
879 views
GCD - is this solution iterative?
Using the property that GCD(a, b) = GCD(b, r) where r is the remainder when you compute (a / b), you can write a recursive function as follows:
...
4
votes
2answers
131 views
Converting English Measurements to Metric and vice versa
I finished answering Exercise 3.3.1 of How to Design Programs where:
Exercise 3.3.1. The United States uses the English system of
(length) measurements. The rest of the world uses the metric ...
4
votes
1answer
239 views
Examine a list for cycles
From SICP:
Exercise 3.18. Write a procedure that
examines a list and determines whether
it contains a cycle, that is, whether
a program that tried to find the end
of the list by taking ...
4
votes
3answers
952 views
Eight-queens puzzle
Figure 2.8: A solution to the
eight-queens puzzle. The
``eight-queens puzzle'' asks how to
place eight queens on a chessboard so
that no queen is in check from any
other (i.e., no two ...
4
votes
1answer
875 views
Abstract tree-map function
Exercise 2.31. Abstract your answer
to exercise 2.30 to produce a
procedure tree-map with the property
that square-tree could be defined as
...
4
votes
1answer
171 views
Is this a good way to implement let-with?
I've implemented a let-with macro that takes an association list, keyed by symbols, that enables code to bind their corresponding values to local variables.
It's ...
4
votes
1answer
94 views
Sieve of Eratosthenes in Scheme (R7RS)
I've seen many implementations of Sieve of Eratosthenes in Scheme, but I thought I'd try to write one that is both space- and time-efficient:
Space-efficient: I use R7RS bytevectors as a bitset, ...
4
votes
2answers
947 views
Reverse in terms of fold-right and fold-left
Exercise 2.39
Complete the following definitions of reverse
(exercise 2.18) in terms of fold-right
and fold-left from exercise 2.38:
...
4
votes
1answer
2k views
Matrix multiplication and dot-product
Exercise 2.37. Suppose we represent
vectors v = (vi) as sequences of
numbers, and matrices m = (mij) as
sequences of vectors (the rows of the
matrix). For example, the matrix
is ...
4
votes
1answer
366 views
Redefine count-leaves as an accumulation
Exercise 2.35. Redefine count-leaves
from section 2.2.2 as an accumulation:
...
4
votes
0answers
152 views
Quick Insert Merge Sort
I have written this code to sort a list of numbers, in increasing order.
It is a combination of quick sort, insertion sort, and merge sort. I make the first element of the list a pivot, then I go ...
3
votes
2answers
95 views
This snippet of scheme calculates a value in pascal's triangle
I'm working through SICP and have implemented exercise 1.11 (Pascal's Triangle). What I'm curious about here is performance considerations by defining functions within the main function. I would ...
3
votes
2answers
554 views
A little scheme programming challenge
I am learning scheme to get something new from a programming language and this code below is the solution to Project Euler question 21 but the code runs 10x slower than the listed Python code when I ...
3
votes
2answers
105 views
split-string for R7RS
A split-string function seems to be missing in R7RS.
I came up with the following implementation today:
...
3
votes
2answers
261 views
Rosalind's 3rd problem in Scheme
I have an imperative programming background and I've decided to study functional programming by applying it to problems found on sites such as Project Euler and Rosalind. My language of choice is ...
3
votes
1answer
794 views
Iterative exponentiation process
From SICP's 1.24: (Exponentiation)
(you may need to click through and read ~1 page to understand)
Exercise 1.16. Design a procedure
that evolves an iterative
exponentiation process that ...
3
votes
1answer
249 views
Extend sums and products functions
Exercise 2.57. Extend the
differentiation program to handle sums
and products of arbitrary numbers of
(two or more) terms. Then the last
example above could be expressed as
...
3
votes
1answer
34 views
Digit Summing Function
I'm working through the common divisibility tests, and implementing them in Racket. I'm working on divisible by three, for which I thought it'd be nice to keep summing until I got to a single digit ...
3
votes
1answer
427 views
Scheme/Racket: idiomatic infix math evaluator
Inspired by xkcd and a couple of praising blog posts, I decided to try out Lisp. It seemed that the best-supported dialect was Racket, itself a variant of Scheme, so I went with that and wrote an ...
3
votes
1answer
243 views
A Simple Unix Filter in Racket - Learning the Racket Way
I've written the following simple filter in Racket as my first Racket program and am wondering if I am writing it in an "idiomatic Racket style".
...
3
votes
1answer
345 views
Scheme, first timer first program, simple list removal technique
I have started my hand at writing some scheme code. I am trying to get the first n primes. I plan to do so but first getting a list from 2 to ...
3
votes
1answer
581 views
A list builder or list accumulator
Imagine a UTF-8 decoder that takes a list of bytes and
returns humman readable code points like:
...
3
votes
0answers
105 views
Graphical editor with geometric intersection
If it is possible I would like some comments on the overall style of the program. It feels like I am writing the whole program as one big script and I'm not sure how to break it down into several ...
3
votes
0answers
135 views
Representing a queue as a procedure with local state
From SICP:
Exercise 3.22. Instead of
representing a queue as a pair of
pointers, we can build a queue as a
procedure with local state. The local
state will consist of pointers to the
...
3
votes
3answers
80 views
Sum of squares of 2 largest numbers out of a list of 3 numbers
The problem is:
Define a procedure that takes 3 number arguments and returns the sum of the squares of the 2 largest numbers.
I am a CS graduate and I am revising my university notes. This is my ...
2
votes
3answers
249 views
Splitting a list in Racket
I am working my way into learning a bit of Scheme (actually, Racket) with the help of a few practical problems to solve. In this case, I want to split a flat list of symbols at a certain delimiter ...
2
votes
2answers
1k views
Use Newton's Method to compute sqrt(x)
Given the following task:
Use Newton's method to compute the square root of a number. Newton's
method involves successive approximation. You start with a guess, and
then continue averaging ...
2
votes
1answer
595 views
An in-nested sequence generator for racket scheme
I've been learning about racket sequences and noticed a hole where nested iteration is concerned. We have the in-parallel construct but no ...
2
votes
1answer
2k views
Pascal's triangle
1
1 1
1 2 1
1 3 3 1
What do you think of this solution for computing Pascal's triangle?
...
2
votes
1answer
351 views
Solving the N-queens puzzle the Racket or Scheme way
My final version is a direct translation from Python. Thanks to build-in support for generator, its speed is almost the same as Python. As I quite like using generator and list comprehension in ...
