I am having two problems while working in Lisp and I can't find any tutorials or sites that explain this. How do you split up a string into its individual characters? And how would I be able to change those characters into their corresponding ASCII values? If anyone knows any sites or tutorial videos explaining these, they would be greatly appreciated.
CL-USER 87 > (coerce "abc" 'list)
(#\a #\b #\c)
CL-USER 88 > (map 'list #'char-code "abc")
(97 98 99)
Get the Common Lisp Quick Reference.
A Lisp string is already split into its characters, in a way. It is a vector of characters, and depending upon what you need to do, you can use either whole string operations on it, or any operations applicable to vectors (like all the operations of the sequence protocol) to handle the individual characters.
split-string splits string into substrings based on the regular expression separators
Each match for separators defines a splitting point; the substrings between splitting points are made into a list, which is returned. If omit-nulls is nil (or omitted), the result contains null strings whenever there are two consecutive matches for separators, or a match is adjacent to the beginning or end of string. If omit-nulls is t, these null strings are omitted from the result. If separators is nil (or omitted), the default is the value of split-string-default-separators.
As a special case, when separators is nil (or omitted), null strings are always omitted
from the result. Thus:
(split-string " two words ") -> ("two" "words")
The result is not ("" "two" "words" ""), which would rarely be useful. If you need
such a result, use an explicit value for separators:
(split-string " two words " split-string-default-separators) -> ("" "two" "words" "")
More examples:
(split-string "Soup is good food" "o") -> ("S" "up is g" "" "d f" "" "d")
(split-string "Soup is good food" "o" t) -> ("S" "up is g" "d f" "d")
(split-string "Soup is good food" "o+") -> ("S" "up is g" "d f" "d")
You can also use elt or aref to get specific characters out of a string.
One of the best sites for an in-depth introduction to Common Lisp is the site for the Practical Common Lisp book (link to the section on numbers, chars and strings). The whole book is available online for free. Check it out.
Related
Solving Advent of Code 2015 task 8 part2 I encountered the problem to have to distinguish in a string the occurrence of "\x27" from plain "x27".
But I don't see a way how I can do it. Because
(length "\x27") ;; is 3
(length "x27") ;; is also 3
(subseq "\x27" 0 1) ;; is "x"
(subseq "x27" 0 1) ;; is "x"
Neither print, prin1, princ made a difference.
# nor does `coerce`
(coerce "\x27" 'list)
;; (#\x #\2 #\7)
So how then to distinguish in a string when "\x27" or any of such
hexadecimal representation occurs?
It turned out, one doesn't need to solve this to solve the task. However, now I still would like to know whether there is a way to distinguish "\x" from "x" in common lisp.
The string literal "\x27" is read as the same as "x27", because \ is an escape character in string literals. If you want a string with the contents \x27, you need to write the literal as "\\x27" (i. e. escape the escape character). This has nothing to do with the strings themselves. If you read a string from a file containing \x27 (e. g. with read-line), then the four-character string \x27 results.
By the time that the Lisp reader gets to work, \x is the same as x. There may be some way to turn this off - I wouldn't be surprised - but the original text talks about Santa's file.
So, I created my own file, like this:
x27
\x27
And I read the data into special variables like this:
(defun read-line-crlf (stream)
(string-right-trim '(#\Return) (read-line stream nil)))
(defun read-lines (filename)
(with-open-file (stream filename)
(setf x (read-line-crlf stream))
(setf x-esc (read-line-crlf stream))
))
The length of x is then 3, and the length of x-esc is 4. The returned string must be trimmed on Windows, or an external format declared, because otherwise SBCL will leave half of the CR-LF on the end of the read strings.
Basically I have a problem, here is the information needed to solve the problem.
PigLatin. Pig Latin is a way of rearranging letters in English words for fun. For example, the sentence “pig latin is stupid” becomes “igpay atinlay isway upidstay”.
Vowels(‘a’,‘e’,‘i’,‘o’,and‘u’)are treated separately from the consonants(any letter that isn’t a vowel).
For simplicity, we will consider ‘y’ to always be a consonant. Although various forms of Pig Latin exist, we will use the following rules:
(1) Words of two letters or less simply have “way” added on the end. So “a” becomes “away”.
(2) In any word that starts with consonants, the consonants are moved to the end, and “ay” is added. If a word begins with more than two consonants, move only the first two letters. So “hello” becomes “ellohay”, and “string” becomes “ringstay”.
(3) Any word which begins with a vowel simply has “way” added on the end. So “explain” becomes “explainway”.
Write a function (pig-latin L) that consumes a non-empty (listof Str) and returns a Str containing the words in L converted to Pig Latin.
Each value in L should contain only lower case letters and have a length of at least 1.
I understand that i need to set three main conditions here, i'm struggling with Racket and learning the proper syntax to write out my solutions. first I need to make a conditions that looks at a string and see if it's length is 2 or less to meet the (1) condition. For (2) I need to look at the first two characters in a string, i'm assuming I have to convert the string into a list of char(string->list). For (3) I understand I just have to look at the first character in the string, i basically have to repeat what I did with (2) but just look at the first character.
I don't know how to manipulate a list of char though. I also don't know how to make sure string-length meets a criteria. Any assistance would be appreciated. I basically have barely any code for my problem since I am baffled on what to do here.
An example of the problem is
(pig-latin (list "this" "is" "a" "crazy" "exercise")) =>
"isthay isway away azycray exerciseway"
The best strategy to solve this problem is:
Check in the documentation all the available string procedures. We don't need to transform the input string to a list of chars to operate upon it, and you'll find that there are existing procedures that meet all of our needs.
Write helper procedures. In fact, we only need a procedure that tells us if a string contains a vowel at a given position; the problem states that only a-z characters are used so we can negate this procedure to also find consonants.
It's also important to identify the best order to write the conditions, for example: conditions 1 and 3 can be combined in a single case. This is my proposal:
(define (vowel-at-index? text index)
(member (string-ref text index)
'(#\a #\e #\i #\o #\u)))
(define (pigify text)
; cases 1 and 3
(cond ((or (<= (string-length text) 2)
(vowel-at-index? text 0))
(string-append text "way"))
; case 2.1
((and (not (vowel-at-index? text 0))
(vowel-at-index? text 1))
(string-append (substring text 1)
(substring text 0 1)
"ay"))
; case 2.2
(else
(string-append (substring text 2)
(substring text 0 2)
"ay"))))
(define (pig-latin lst)
(string-join (map pigify lst)))
For the final step, we only need to apply the pigify procedure to each element in the input, and that's what map does. It works as expected:
(pig-latin '("this" "is" "a" "crazy" "exercise"))
=> "isthay isway away azycray exerciseway"
I have a string in Clojure and a character I want to put in between the nth and (n+1)st character. For example: Lets say the string is "aple" and I want to insert another "p" between the "p" and the "l".
(prn
(some-function "aple" "p" 1 2))
;; prints "apple"
;; ie "aple" -> "ap" "p" "le" and the concatenated back together.
I'm finding this somewhat challenging, so I figure I am missing information about some useful function(s) Can someone please help me write the "some-function" above that takes a string, another string, a start position and an end position and inserts the second string into the first between the start position and the end position? Thanks in advance!
More efficient than using seq functions:
(defn str-insert
"Insert c in string s at index i."
[s c i]
(str (subs s 0 i) c (subs s i)))
From the REPL:
user=> (str-insert "aple" "p" 1)
"apple"
NB. This function doesn't actually care about the type of c, or its length in the case of a string; (str-insert "aple" \p 1) and (str-insert "ale" "pp" 1) work also (in general, (str c) will be used, which is the empty string if c is nil and (.toString c) otherwise).
Since the question asks for an idiomatic way to perform the task at hand, I will also note that I find it preferable (in terms of "semantic fit" in addition to the performance advantage) to use string-oriented functions when dealing with strings specifically; this includes subs and functions from clojure.string. See the design notes at the top of the source of clojure.string for a discussion of idiomatic string handling.
I've been looking for a way to convert user input (read-line) to a list of atoms that I can manipulate more easily.
For example:
SendInput()
This is my input. Hopefully this works.
and I want to get back..
(This is my input. Hopefully this works.)
Eventually it'd be ideal to remove any periods, commas, quotes, etc. But for now I just wanna store the users input in a list (NOT AS A STRING)
So. For now i'm using
(setf stuff (coerce (read-line) 'list))
and that returns to me as...
(#\T #\h #\i #\s #\Space #\i #\s #\Space #\m #\y #\Space #\i #\n #\p #\u #\t #. #\Space #\H #\o #\p #\e #\f #\u #\l #\l #\y #\Space #\t #\h #\i #\s #\Space #\w #\o #\r #\k #\s #.)
So now i'm on the hunt for a function that can take that list and format it properly...
Any help would be greatly appreciated!
Rainer's answer is better in that it's a bit more lightweight (and general), but you could also use CL-PPCRE , if you already have it loaded (I know I always do).
You can use SPLIT directly on the string you get from READ-LINE, like so:
(cl-ppcre:split "[ .]+" (read-line))
(Now you have two problems)
What you want to do is to split a sequence of characters (a String) into a list of smaller strings or symbols.
Use some of the split sequence functions available from a Lisp library (see for example cl-utilities).
In LispWorks, which comes with a SPLIT-SEQUENCE function) I would for example write:
CL-USER 8 > (mapcar #'intern
(split-sequence '(#\space #\.)
"This is my input. Hopefully this works."
:coalesce-separators t))
(|This| |is| |my| |input| |Hopefully| |this| |works|)
Remember, to get symbols with case preserving names, they are surrounded by vertical bars. The vertical bars are not part of the symbol name - just like the double quotes are not part of a string - they are delimiters.
You can also print it:
CL-USER 19 > (princ (mapcar #'intern
(split-sequence '(#\space #\.)
"This is my input. Hopefully this works."
:coalesce-separators t)))
(This is my input Hopefully this works)
(|This| |is| |my| |input| |Hopefully| |this| |works|)
Above prints the list. The first output is the data printed by PRINC and the second output is done by the REPL.
If you don't want symbols, but strings:
CL-USER 9 > (split-sequence '(#\space #\.)
"This is my input. Hopefully this works."
:coalesce-separators t)
("This" "is" "my" "input" "Hopefully" "this" "works")
I am passing in command line arguments to my Lisp program and they are formatted like this when they hit my main function:
("1 1 1" "dot" "2 2 2")
I have a dot function (which takes two vectors as arguments) and would like to call it directly from the argument, but this isn't possible because something like (funcall (second args)...) receives "dot" and not dot as the function name.
I tried variations of this function:
(defun remove-quotes (s)
(setf (aref s 0) '""))
to no avail, before realizing that the quotes were not really a part of the string. Is there a simple way to do this, or should I just check each string and then call the appropriate function?
"1 1 1" is a string of five characters: 1, space, 1, space and 1. The double quotes are not part of the string.
("1 1 1" "dot" "2 2 2") is a list of three strings.
There are no " characters above. The " are used to delimit strings in s-expressions.
If you have a dot function you need to tell us what kind of input data it expects.
Does it expect two lists of numbers? Then you have to convert the string "1 1 1" into a list of numbers.
(with-input-from-string (in "1 1 1")
(loop for data = (read in nil in)
until (eq data in)
collect data)))
To get the function DOT from the string "dot" first find the symbol DOT and then get its symbol function.
(symbol-function (find-symbol (string-upcase "dot")))
For find-symbol one might need to specify also the package, if there is a special package where the symbol is in.
Converting a list to a vector then is the next building block.
So you need to convert the arguments for your function to vectors (probably first converting them to lists as I showed above). Then you need to find the function (see above). If you have then the function and the arguments, then you can call the function using FUNCALL or APPLY (whatever is more convenient).
The question is a bit unclear, but as far as I understand it you want, when given the list ("1 1 1" "dot" "2 2 2") as input to evaluate the expression (dot "1 1 1" "2 2 2"). In that case you can do this:
(defun apply-infix (arg1 f arg2)
(apply (intern (string-upcase f)) (list arg1 arg2)))
(defun apply-list-infix (lst)
(apply 'apply-infix lst))
(apply-list-infix '("1 1 1" "dot" "2 2 2"))
funcall does not accept a string as a function designator. You need to give it a symbol instead. What you probably want to do is:
Convert the string to upper case (Lisp symbols are usually upper case, and even though it may look like Lisp is case-insensitive, that's just because the reader upcases all symbols it reads by default) (string-upcase).
Create or find a symbol with the given name (intern). Note that, if *package* is not set according to the package your function's name lives in, you need to supply the package name as the second argument to intern.
For instance (for a function named dot in package cl-user:
(funcall (intern (string-upcase "dot") 'cl-user) ...)