341 lines
No EOL
7 KiB
HTML
341 lines
No EOL
7 KiB
HTML
<!DOCTYPE HTML>
|
|
<HTML LANG="en-us"
|
|
><HEAD
|
|
><TITLE
|
|
>block | Common Lisp Nova Spec</TITLE
|
|
><META CHARSET="US-ASCII"
|
|
><LINK REL="canonical" HREF="f_block.html"
|
|
><LINK REL="next" HREF="f_catch.html" TYPE="text/html" TITLE="catch"
|
|
><LINK REL="prev" HREF="f_psetq.html" TYPE="text/html" TITLE="psetq"
|
|
><LINK REL="up" HREF="5_3_Data_and_Control_Flow_Dictionary.html" TYPE="text/html" TITLE="5.3 Data and Control Flow 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"
|
|
>→ <A HREF="5_Data_and_Control_Flow.html"
|
|
>5. Data and Control Flow</A
|
|
></SPAN
|
|
> <SPAN CLASS="breadcrumb-item"
|
|
>→ <A HREF="5_3_Data_and_Control_Flow_Dictionary.html"
|
|
>5.3 Data and Control Flow Dictionary</A
|
|
></SPAN
|
|
> <SPAN CLASS="breadcrumb-item"
|
|
>→ <A HREF="f_block.html"
|
|
>block</A
|
|
></SPAN
|
|
></DIV
|
|
><DIV CLASS="apropos"
|
|
><DIV CLASS="apropos-io"
|
|
><A HREF="f_psetq.html" CLASS="prev"
|
|
>←</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_catch.html" CLASS="next"
|
|
>→</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="block"
|
|
></SPAN
|
|
><B
|
|
>block</B
|
|
></TD
|
|
><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
|
|
><I
|
|
>Special</I
|
|
> <I
|
|
>Operator</I
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
></DIV
|
|
><UL CLASS="subtoc"
|
|
></UL
|
|
><DL
|
|
><DT
|
|
><B
|
|
>Syntax</B
|
|
></DT
|
|
><DD
|
|
><P CLASS="j"
|
|
><B
|
|
>block</B
|
|
> <VAR CLASS="param"
|
|
>name</VAR
|
|
> <VAR CLASS="param"
|
|
>form</VAR
|
|
>* <SPAN CLASS="arrow"
|
|
>→</SPAN
|
|
> {<VAR CLASS="param"
|
|
>result</VAR
|
|
>}*</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>Arguments and Values</B
|
|
></DT
|
|
><DD
|
|
><P CLASS="j"
|
|
><VAR CLASS="param"
|
|
>name</VAR
|
|
> — a <A HREF="26_1_Glossary.html#symbol"
|
|
><EM CLASS="term"
|
|
>symbol</EM
|
|
></A
|
|
>. </P
|
|
><P CLASS="j"
|
|
><VAR CLASS="param"
|
|
>form</VAR
|
|
> — a <A HREF="26_1_Glossary.html#form"
|
|
><EM CLASS="term"
|
|
>form</EM
|
|
></A
|
|
>. </P
|
|
><P CLASS="j"
|
|
><VAR CLASS="param"
|
|
>results</VAR
|
|
> — the <A HREF="26_1_Glossary.html#value"
|
|
><EM CLASS="term"
|
|
>values</EM
|
|
></A
|
|
> of the <A HREF="26_1_Glossary.html#form"
|
|
><EM CLASS="term"
|
|
>forms</EM
|
|
></A
|
|
> if a <A HREF="26_1_Glossary.html#normal_return"
|
|
><EM CLASS="term"
|
|
>normal return</EM
|
|
></A
|
|
> occurs, or else, if an <A HREF="26_1_Glossary.html#explicit_return"
|
|
><EM CLASS="term"
|
|
>explicit return</EM
|
|
></A
|
|
> occurs, the <A HREF="26_1_Glossary.html#value"
|
|
><EM CLASS="term"
|
|
>values</EM
|
|
></A
|
|
> that were transferred.</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>Description</B
|
|
></DT
|
|
><DD
|
|
><P CLASS="j"
|
|
><A HREF="f_block.html" CLASS="specref"
|
|
><B
|
|
>block</B
|
|
></A
|
|
> <A HREF="26_1_Glossary.html#establish"
|
|
><EM CLASS="term"
|
|
>establishes</EM
|
|
></A
|
|
> a <A HREF="26_1_Glossary.html#block"
|
|
><EM CLASS="term"
|
|
>block</EM
|
|
></A
|
|
> named <VAR CLASS="param"
|
|
>name</VAR
|
|
> and then evaluates <VAR CLASS="param"
|
|
>forms</VAR
|
|
> as an <A HREF="26_1_Glossary.html#implicit_progn"
|
|
><EM CLASS="term"
|
|
>implicit progn</EM
|
|
></A
|
|
>. </P
|
|
><P CLASS="j"
|
|
>The <A HREF="26_1_Glossary.html#special_operator"
|
|
><EM CLASS="term"
|
|
>special operators</EM
|
|
></A
|
|
> <A HREF="f_block.html" CLASS="specref"
|
|
><B
|
|
>block</B
|
|
></A
|
|
> and <A HREF="f_return-from.html" CLASS="specref"
|
|
><B
|
|
>return-from</B
|
|
></A
|
|
> work together to provide a structured, lexical, non-local exit facility. At any point lexically contained within <A HREF="26_1_Glossary.html#form"
|
|
><EM CLASS="term"
|
|
>forms</EM
|
|
></A
|
|
>, <A HREF="f_return-from.html" CLASS="specref"
|
|
><B
|
|
>return-from</B
|
|
></A
|
|
> can be used with the given <VAR CLASS="param"
|
|
>name</VAR
|
|
> to return control and values from the <A HREF="f_block.html" CLASS="specref"
|
|
><B
|
|
>block</B
|
|
></A
|
|
> <A HREF="26_1_Glossary.html#form"
|
|
><EM CLASS="term"
|
|
>form</EM
|
|
></A
|
|
>, except when an intervening <A HREF="26_1_Glossary.html#block"
|
|
><EM CLASS="term"
|
|
>block</EM
|
|
></A
|
|
> with the same name has been <A HREF="26_1_Glossary.html#establish"
|
|
><EM CLASS="term"
|
|
>established</EM
|
|
></A
|
|
>, in which case the outer <A HREF="26_1_Glossary.html#block"
|
|
><EM CLASS="term"
|
|
>block</EM
|
|
></A
|
|
> is shadowed by the inner one. </P
|
|
><P CLASS="j"
|
|
>The <A HREF="26_1_Glossary.html#block"
|
|
><EM CLASS="term"
|
|
>block</EM
|
|
></A
|
|
> named <A HREF="26_1_Glossary.html#name"
|
|
><EM CLASS="term"
|
|
>name</EM
|
|
></A
|
|
> has <A HREF="26_1_Glossary.html#lexical_scope"
|
|
><EM CLASS="term"
|
|
>lexical scope</EM
|
|
></A
|
|
> and <A HREF="26_1_Glossary.html#dynamic_extent"
|
|
><EM CLASS="term"
|
|
>dynamic extent</EM
|
|
></A
|
|
>. </P
|
|
><P CLASS="j"
|
|
>Once established, a <A HREF="26_1_Glossary.html#block"
|
|
><EM CLASS="term"
|
|
>block</EM
|
|
></A
|
|
> may only be exited once, whether by <A HREF="26_1_Glossary.html#normal_return"
|
|
><EM CLASS="term"
|
|
>normal return</EM
|
|
></A
|
|
> or <A HREF="26_1_Glossary.html#explicit_return"
|
|
><EM CLASS="term"
|
|
>explicit return</EM
|
|
></A
|
|
>.</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>Examples</B
|
|
></DT
|
|
><DD
|
|
><PRE CLASS="screen"
|
|
>(block empty) <SPAN CLASS="cmsy"
|
|
><SPAN CLASS="arrow"
|
|
>→</SPAN
|
|
></SPAN
|
|
> NIL
|
|
(block whocares (values 1 2) (values 3 4)) <SPAN CLASS="cmsy"
|
|
><SPAN CLASS="arrow"
|
|
>→</SPAN
|
|
></SPAN
|
|
> 3, 4
|
|
(let ((x 1))
|
|
(block stop (setq x 2) (return-from stop) (setq x 3))
|
|
x) <SPAN CLASS="cmsy"
|
|
><SPAN CLASS="arrow"
|
|
>→</SPAN
|
|
></SPAN
|
|
> 2
|
|
(block early (return-from early (values 1 2)) (values 3 4)) <SPAN CLASS="cmsy"
|
|
><SPAN CLASS="arrow"
|
|
>→</SPAN
|
|
></SPAN
|
|
> 1, 2
|
|
(block outer (block inner (return-from outer 1)) 2) <SPAN CLASS="cmsy"
|
|
><SPAN CLASS="arrow"
|
|
>→</SPAN
|
|
></SPAN
|
|
> 1
|
|
(block twin (block twin (return-from twin 1)) 2) <SPAN CLASS="cmsy"
|
|
><SPAN CLASS="arrow"
|
|
>→</SPAN
|
|
></SPAN
|
|
> 2
|
|
;; Contrast behavior of this example with corresponding example of CATCH.
|
|
(block b
|
|
(flet ((b1 () (return-from b 1)))
|
|
(block b (b1) (print 'unreachable))
|
|
2)) <SPAN CLASS="cmsy"
|
|
><SPAN CLASS="arrow"
|
|
>→</SPAN
|
|
></SPAN
|
|
> 1</PRE
|
|
></DD
|
|
><DT
|
|
><B
|
|
>See Also</B
|
|
></DT
|
|
><DD
|
|
><P CLASS="j"
|
|
><A HREF="f_return.html" CLASS="macref"
|
|
><B
|
|
>return</B
|
|
></A
|
|
>, <A HREF="f_return-from.html" CLASS="specref"
|
|
><B
|
|
>return-from</B
|
|
></A
|
|
>, <A HREF="3_1_Evaluation.html#sec_3_1" CLASS="secref"
|
|
><SPAN CLASS="cmr"
|
|
>Section</SPAN
|
|
> <SPAN CLASS="cmr"
|
|
>3.1</SPAN
|
|
> <SPAN CLASS="cmr"
|
|
>(Evaluation)</SPAN
|
|
></A
|
|
></P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>Notes</B
|
|
></DT
|
|
></DL
|
|
></DIV
|
|
></DIV
|
|
><DIV CLASS="footer"
|
|
><DIV CLASS="btmnav"
|
|
><A HREF="f_psetq.html" CLASS="prev"
|
|
>←</A
|
|
><A HREF="f_catch.html" CLASS="next"
|
|
>→</A
|
|
></DIV
|
|
><DIV CLASS="trail"
|
|
>Conversion to HTML copyright 2023 by Gilbert Baumann</DIV
|
|
></DIV
|
|
></DIV
|
|
><SCRIPT
|
|
>domReady();</SCRIPT
|
|
></BODY
|
|
></HTML
|
|
> |