marcuskammer/cl-sites
1
0
Fork 0
Code Activity
cl-sites/novaspec.org/cl/f_butlast.html
Marcus Kammer 00674f4c59
Add novaspec
2025-02-05 18:52:26 +01:00

390 lines
No EOL
7.4 KiB
HTML
Raw Blame History

<!DOCTYPE HTML>
<HTML LANG="en-us"
><HEAD
><TITLE
>butlast, nbutlast | Common Lisp Nova Spec</TITLE
><META CHARSET="US-ASCII"
><LINK REL="canonical" HREF="f_butlast.html"
><LINK REL="next" HREF="f_last.html" TYPE="text/html" TITLE="last"
><LINK REL="prev" HREF="f_revappend.html" TYPE="text/html" TITLE="revappend, nreconc"
><LINK REL="up" HREF="14_2_Conses_Dictionary.html" TYPE="text/html" TITLE="14.2 Conses Dictionary"
><LINK REL="start" HREF="index.html" TYPE="text/html" TITLE="Common Lisp Nova Spec"
><META NAME="VIEWPORT" CONTENT="width=device-width, initial-scale=1.0"
><LINK REL="STYLESHEET" HREF="dpans.css%3F3909942064.css"
><SCRIPT SRC="dpans.js%3F3909942064"
></SCRIPT
><SCRIPT SRC="apropos.js%3F3909942064"
></SCRIPT
></HEAD
><BODY
><DIV
><DIV CLASS="topnav"
><DIV CLASS="breadcrumb"
><SPAN CLASS="breadcrumb-item"
><A HREF="index.html"
>Common Lisp Nova Spec</A
></SPAN
> <SPAN CLASS="breadcrumb-item"
>&#8594; <A HREF="14_Conses.html"
>14. Conses</A
></SPAN
> <SPAN CLASS="breadcrumb-item"
>&#8594; <A HREF="14_2_Conses_Dictionary.html"
>14.2 Conses Dictionary</A
></SPAN
> <SPAN CLASS="breadcrumb-item"
>&#8594; <A HREF="f_butlast.html"
>butlast, nbutlast</A
></SPAN
></DIV
><DIV CLASS="apropos"
><DIV CLASS="apropos-io"
><A HREF="f_revappend.html" CLASS="prev"
>&#8592;</A
><SPAN ID="apropos-label"
>Apropos </SPAN
><INPUT ID="apropos" AUTOFOCUS="AUTOFOCUS" PLACEHOLDER="Type here to search" ONINPUT="aproposInput(this);" ONKEYUP="aproposKeyup(event);" ONCHANGE="aproposChange(this);" ONFOCUS="aproposFocus(this);" ONFOCUSOUT="aproposFocusout(this);"
><A HREF="f_last.html" CLASS="next"
>&#8594;</A
></DIV
><DIV ID="apropos-res"
></DIV
></DIV
></DIV
><DIV CLASS="matter"
><DIV CLASS="com"
><DIV CLASS="begincom"
><HR
><TABLE WIDTH="100%" CELLSPACING="0" CELLPADDING="0"
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" WIDTH="100%" CLASS="name"
><SPAN CLASS="idx" DATA-KIND="idxref" DATA-TERM="butlast, nbutlast"
></SPAN
><B
>butlast, nbutlast</B
></TD
><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
><I
>Function</I
></TD
></TR
></TABLE
><HR
></DIV
><UL CLASS="subtoc"
></UL
><DL
><DT
><B
>Syntax</B
></DT
><DD
><P CLASS="j"
><B
>butlast</B
> <SPAN CLASS="cmssi"
>list</SPAN
> <SPAN CLASS="cmtt"
>&amp;optional</SPAN
> <SPAN CLASS="cmssi"
>n</SPAN
> <SPAN CLASS="arrow"
>&#8594;</SPAN
> <SPAN CLASS="cmssi"
>result-list</SPAN
></P
><P CLASS="j"
><B
>nbutlast</B
> <SPAN CLASS="cmssi"
>list</SPAN
> <SPAN CLASS="cmtt"
>&amp;optional</SPAN
> <SPAN CLASS="cmssi"
>n</SPAN
> <SPAN CLASS="arrow"
>&#8594;</SPAN
> <SPAN CLASS="cmssi"
>result-list</SPAN
></P
></DD
><DT
><B
>Arguments and Values</B
></DT
><DD
><P CLASS="j"
><VAR CLASS="param"
>list</VAR
> &#8212; a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
>, which might be a <A HREF="26_1_Glossary.html#dotted_list"
><EM CLASS="term"
>dotted list</EM
></A
> but must not be a <A HREF="26_1_Glossary.html#circular_list"
><EM CLASS="term"
>circular list</EM
></A
>. </P
><P CLASS="j"
><VAR CLASS="param"
>n</VAR
> &#8212; a non-negative <A HREF="26_1_Glossary.html#integer"
><EM CLASS="term"
>integer</EM
></A
>. </P
><P CLASS="j"
><VAR CLASS="param"
>result-list</VAR
> &#8212; a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
>.</P
></DD
><DT
><B
>Description</B
></DT
><DD
><P CLASS="j"
><A HREF="f_butlast.html" CLASS="funref"
><B
>butlast</B
></A
> returns a copy of <VAR CLASS="param"
>list</VAR
> from which the last <VAR CLASS="param"
>n</VAR
> conses have been omitted. If <VAR CLASS="param"
>n</VAR
> is not supplied, its value is 1. If there are fewer than <VAR CLASS="param"
>n</VAR
> conses in <VAR CLASS="param"
>list</VAR
>, <SPAN CLASS="misc"
><B
>nil</B
></SPAN
> is returned and, in the case of <A HREF="f_butlast.html" CLASS="funref"
><B
>nbutlast</B
></A
>, <VAR CLASS="param"
>list</VAR
> is not modified. </P
><P CLASS="j"
><A HREF="f_butlast.html" CLASS="funref"
><B
>nbutlast</B
></A
> is like <A HREF="f_butlast.html" CLASS="funref"
><B
>butlast</B
></A
>, but <A HREF="f_butlast.html" CLASS="funref"
><B
>nbutlast</B
></A
> may modify <VAR CLASS="param"
>list</VAR
>. It changes the <A HREF="26_1_Glossary.html#cdr"
><EM CLASS="term"
>cdr</EM
></A
> of the <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>cons</EM
></A
> <VAR CLASS="param"
>n</VAR
>+1 from the end of the <VAR CLASS="param"
>list</VAR
> to <SPAN CLASS="misc"
><B
>nil</B
></SPAN
>.</P
></DD
><DT
><B
>Examples</B
></DT
><DD
><PRE CLASS="screen"
>(setq lst '(1 2 3 4 5 6 7 8 9)) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (1 2 3 4 5 6 7 8 9)
(butlast lst) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (1 2 3 4 5 6 7 8)
(butlast lst 5) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (1 2 3 4)
(butlast lst (+ 5 5)) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> NIL
lst <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (1 2 3 4 5 6 7 8 9)
(nbutlast lst 3) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (1 2 3 4 5 6)
lst <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (1 2 3 4 5 6)
(nbutlast lst 99) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> NIL
lst <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (1 2 3 4 5 6)
(butlast '(a b c d)) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (A B C)
(butlast '((a b) (c d))) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> ((A B))
(butlast '(a)) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> NIL
(butlast nil) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> NIL
(setq foo (list 'a 'b 'c 'd)) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (A B C D)
(nbutlast foo) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (A B C)
foo <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> (A B C)
(nbutlast (list 'a)) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> NIL
(nbutlast '()) <SPAN CLASS="cmsy"
><SPAN CLASS="arrow"
>&#8594;</SPAN
></SPAN
> NIL</PRE
></DD
><DT
><B
>Exceptional Situations</B
></DT
><DD
><P CLASS="j"
>Should signal an error of <A HREF="26_1_Glossary.html#type"
><EM CLASS="term"
>type</EM
></A
> <A HREF="t_type-error.html" CLASS="typeref"
><B
>type-error</B
></A
> if <VAR CLASS="param"
>list</VAR
> is not a <A HREF="26_1_Glossary.html#proper_list"
><EM CLASS="term"
>proper list</EM
></A
> or a <A HREF="26_1_Glossary.html#dotted_list"
><EM CLASS="term"
>dotted list</EM
></A
>. Should signal an error of <A HREF="26_1_Glossary.html#type"
><EM CLASS="term"
>type</EM
></A
> <A HREF="t_type-error.html" CLASS="typeref"
><B
>type-error</B
></A
> if <VAR CLASS="param"
>n</VAR
> is not a non-negative <A HREF="26_1_Glossary.html#integer"
><EM CLASS="term"
>integer</EM
></A
>.</P
></DD
><DT
><B
>Notes</B
></DT
><DD
><PRE CLASS="screen"
>(butlast <VAR CLASS="param"
>list</VAR
> <VAR CLASS="param"
>n</VAR
>) <SPAN CLASS="cmsy"
><SPAN STYLE="font-size:16px;vertical-align:-2px"
>&#8801;</SPAN
></SPAN
> (ldiff <VAR CLASS="param"
>list</VAR
> (last <VAR CLASS="param"
>list</VAR
> <VAR CLASS="param"
>n</VAR
>))</PRE
></DD
></DL
></DIV
></DIV
><DIV CLASS="footer"
><DIV CLASS="btmnav"
><A HREF="f_revappend.html" CLASS="prev"
>&#8592;</A
><A HREF="f_last.html" CLASS="next"
>&#8594;</A
></DIV
><DIV CLASS="trail"
>Conversion to HTML copyright 2023 by Gilbert Baumann</DIV
></DIV
></DIV
><SCRIPT
>domReady();</SCRIPT
></BODY
></HTML
>
View git blame Copy permalink