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diff --git a/system/doc/extensions/misc.xml b/system/doc/extensions/misc.xml deleted file mode 100644 index 576f705278..0000000000 --- a/system/doc/extensions/misc.xml +++ /dev/null @@ -1,310 +0,0 @@ -<?xml version="1.0" encoding="latin1" ?> -<!DOCTYPE chapter SYSTEM "chapter.dtd"> - -<chapter> - <header> - <copyright> - <year>1999</year><year>2009</year> - <holder>Ericsson AB. All Rights Reserved.</holder> - </copyright> - <legalnotice> - The contents of this file are subject to the Erlang Public License, - Version 1.1, (the "License"); you may not use this file except in - compliance with the License. You should have received a copy of the - Erlang Public License along with this software. If not, it can be - retrieved online at http://www.erlang.org/. - - Software distributed under the License is distributed on an "AS IS" - basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See - the License for the specific language governing rights and limitations - under the License. - - </legalnotice> - - <title>Miscellaneous</title> - <prepared>Arndt Jonasson</prepared> - <docno>1</docno> - <date>99-01-25</date> - <rev>PA1</rev> - <file>misc.sgml</file> - </header> - <p>In this chapter, a number of miscellaneous features of Erlang - are described.</p> - - <section> - <title>Token Syntax</title> - <p>In Erlang 4.8 (OTP R5A) the syntax of Erlang tokens have been - extended to allow the use of the full ISO-8859-1 (Latin-1) character - set. This is noticeable in the following ways:</p> - <list type="bulleted"> - <item>All the Latin-1 printable characters can be used and are shown without - the escape backslash convention.</item> - <item>Atoms and variables can use all Latin-1 letters.</item> - </list> - <p>The new characters from Latin-1 have the following - classifications in Erlang:</p> - <table> - <row> - <cell align="left" valign="middle"><em>Octal</em></cell> - <cell align="left" valign="middle"><em>Decimal</em></cell> - <cell align="left" valign="middle"> </cell> - <cell align="left" valign="middle"><em>Class</em></cell> - </row> - <row> - <cell align="left" valign="middle">200 - 237</cell> - <cell align="left" valign="middle">128 - 159</cell> - <cell align="left" valign="middle"> </cell> - <cell align="left" valign="middle">Control characters</cell> - </row> - <row> - <cell align="left" valign="middle">240 - 277</cell> - <cell align="left" valign="middle">160 - 191</cell> - <cell align="right" valign="middle">- ¿</cell> - <cell align="left" valign="middle">Punctuation characters</cell> - </row> - <row> - <cell align="left" valign="middle">300 - 326</cell> - <cell align="left" valign="middle">192 - 214</cell> - <cell align="center" valign="middle">À - Ö</cell> - <cell align="left" valign="middle">Uppercase letters</cell> - </row> - <row> - <cell align="center" valign="middle">327</cell> - <cell align="center" valign="middle">215</cell> - <cell align="center" valign="middle">×</cell> - <cell align="left" valign="middle">Punctuation character</cell> - </row> - <row> - <cell align="left" valign="middle">330 - 336</cell> - <cell align="left" valign="middle">216 - 222</cell> - <cell align="center" valign="middle">Ø - Þ</cell> - <cell align="left" valign="middle">Uppercase letters</cell> - </row> - <row> - <cell align="left" valign="middle">337 - 366</cell> - <cell align="left" valign="middle">223 - 246</cell> - <cell align="center" valign="middle">ß - ö</cell> - <cell align="left" valign="middle">Lowercase letters</cell> - </row> - <row> - <cell align="center" valign="middle">367</cell> - <cell align="center" valign="middle">247</cell> - <cell align="center" valign="middle">÷</cell> - <cell align="left" valign="middle">Punctuation character</cell> - </row> - <row> - <cell align="left" valign="middle">370 - 377</cell> - <cell align="left" valign="middle">248 - 255</cell> - <cell align="center" valign="middle">ø - ÿ</cell> - <cell align="left" valign="middle">Lowercase letters</cell> - </row> - <tcaption>Character classes</tcaption> - </table> - </section> - - <section> - <title>String Concatenation</title> - <p>Two adjacent string literals are concatenated into one. This is done already - at compile-time, and doesn't incur any runtime overhead. Example:</p> - <code type="none"> - "string" "42" </code> - <p>is equivalent to</p> - <code type="none"> - "string42" </code> - <p>This feature is convenient in at least two situations:</p> - <list type="bulleted"> - <item>when one of the - strings is the result of a macro expansion;</item> - <item>when a string is very - long, and would otherwise either have to wrap, making the source code - harder to read, or force the use of some runtime append operation.</item> - </list> - </section> - - <section> - <title>The ++ list Concatenation Operator</title> - <p>Since list concatenation is a very common operation, it is convenient - to have a terse way of expressing it. The ++ operator appends its second - argument to its first. Example: - </p> - <code type="none"> - X = [1,2,3], - Y = [4,5], - X ++ Y. </code> - <p>results in <c>[1,2,3,4,5]</c>.</p> - <p>The ++ operator has precedence between the binary '+' operator and - the comparison operators. - </p> - </section> - - <section> - <title>The - - list Subtraction Operator</title> - <p>The - - operator produces a list which is a copy of the first - argument, subjected to the following procedure: for each element in - the second argument, its first occurrence in the first argument is - removed.</p> - <code type="none"> - X = [1,2,3,2,1,2], - Y = [2,1,2], - X -- Y. </code> - <p>results in <c>[3,1,2]</c>.</p> - <p>The - - operator has precedence between the binary '+' operator and - the comparison operators. - </p> - </section> - - <section> - <title>Bitwise Operator bnot</title> - <p>Apart from the binary bitwise operators <c>band</c>, <c>bor</c> - and <c>bxor</c>, there is a unary operator <c>bnot</c> with the same - precedence as the other unary operators + and -, i.e., higher than - the binary operators. Example:</p> - <code type="none"> - bnot 7. </code> - <p>returns -8. - </p> - </section> - - <section> - <title>Logical Operators</title> - <p>The atoms <c>true</c> and <c>false</c> are usually used for representing - Boolean values. With the binary operators <c>and</c>, <c>or</c> and - <c>xor</c>, and the unary operator <c>not</c>, Boolean values can be - combined. Example:</p> - <code type="none"> - - M1 = lists:member(A, List1), - M2 = lists:member(A, List2), - M1 and M2.</code> - <p>Note that the operators are strict, i.e., they always evaluate both - their arguments.</p> - <p><c>not</c> has the same priority as the other unary operators. The - binary logical operators have precedence between the <c>=</c> operator - and the comparison operators, the <c>and</c> operator having higher - precedence than <c>or</c> and <c>xor</c>. - </p> - </section> - - <section> - <title>Match Operator = In Patterns</title> - <p>This extension was added in Erlang 4.8 (OTP R5A).</p> - <p>The = operator is also called the `match' operator. The match operator - can now be used in a pattern, so that <c>P1 = P2</c> is a valid pattern, - where both <c>P1</c> and <c>P2</c> are patterns. This compound pattern - when matched against a term causes the term to be matched against both - <c>P1</c> and <c>P2</c>.</p> - <p>One use for this construction is to avoid reconstructing a term which - was part of an argument to a function. Example:</p> - <code type="none"> - f({'+',X,Y}=T) -> {X+Y,T}.</code> - <p>It also makes it possible to rewrite the construction</p> - <code type="none"> - f(X) when X == #rec{x=1, y=a} -> ... </code> - <p>as</p> - <code type="none"> - f(#rec{x=1, y=a} = X) -> ... </code> - <p>In the absence of optimization for the former case, the - latter case is more efficient. - </p> - </section> - - <section> - <title>Literal String Prefix in Patterns</title> - <p>This extension was added in Erlang 4.8 (OTP R5A).</p> - <p>A new construction is allowed in patterns, namely a literal - string as the first operand of the ++ operator. Example:</p> - <code type="none"> - f("prefix" ++ L) -> ... </code> - <p>This is syntactic sugar for the equivalent, but harder to read</p> - <code type="none"> - f([$p,$r,$e,$f,$i,$x | L]) -> ... </code> - </section> - - <section> - <title>Disjunctions in Guards</title> - <p>This extension was added in Erlang 4.9 (OTP R6A).</p> - <p>A new construction is allowed in guards, the disjunction operator - ';'. The construction is syntactic sugar which removes the bother of - writing the same body after several guards.</p> - <code type="none"> - f(X) when xxx ; yyy ; zzz -> - pop(X).</code> - <p>This is syntactic sugar for the equivalent</p> - <code type="none"> - f(X) when xxx -> - pop(X); - f(X) when yyy -> - pop(X); - f(X) when zzz -> - pop(X). </code> - <p>The abstract format has been changed accordingly to contain a list of - (conjunctive) guards where there was previously only one guard. - </p> - </section> - - <section> - <title>Expressions in Patterns</title> - <p>This extension was added in Erlang 5.0 (OTP R7A).</p> - <p>An arithmetic expression can be used within a pattern, if it uses - only numeric or bitwise operators, and if its value can be evaluated - to a constant at compile-time. This is especially useful when the - expression is defined by a macro. - </p> - <p>Example:</p> - <code type="none"> - case X of - {1+2, T} -> T - end.</code> - </section> - - <section> - <title>Boolean expresions in guards</title> - <p>This extension was added in Erlang 5.1 (OTP R8).</p> - <p>In guards, the use of <c>and</c>, <c>or</c> and <c>not</c> is - now allowed. Guard expressions can combine these with - parenthesis. This allows for more elaborate guards than what - may be given with <c>,</c> and <c>;</c>.</p> - <note> - <p>The guard expressions written with these operators are boolean - expressions, and the boolean functions <c>is_list</c>, - <c>is_integer</c> etc. should be used, rather than - <c>list</c>, <c>integer</c> etc.</p> - </note> - <p>Example 1:</p> - <code type="none"> - f(X) when not (is_tuple(X) or is_list(X)) -> - ... </code> - <p>Example 2:</p> - <code type="none"><![CDATA[ - g(A, B) when (A > 0) and (B > 0) and not (A*A < B*B) -> - ... ]]></code> - </section> - - <section> - <title>Short-circuit boolean expressions</title> - <p>This extension was added in Erlang 5.1 (OTP R8).</p> - <p>In a boolean expression it is unnecessary to always evaluate all - terms. If the first term gives a result that determines the - result, the second term is not needed. In Erlang two new - keywords handles boolean expressions without evaluating both - terms, if it's unnecessary. (This is called short-curcuit - boolean evaluation.)</p> - <p>The keyword <c>andalso</c> is a short-curcuit version of - <c>and</c>. The keyword <c>orelse</c> is a short-curcuit version - of <c>or</c>. They can be used in boolean expressions (not - guards) instead of <c>and</c> and <c>or</c>.</p> - <p>Example 1:</p> - <code type="none"> - case A >= -1.0 andalso math:sqrt(A+1) > B of </code> - <p>This will work even if <c>A</c> is less than <c>-1.0</c>, since - in that case, the second term (after <c>andalso</c>) is never - evaluated. (Of course, the same effects could have been done - using guards. In guards, evaluation is always short-circuited, - since guard tests are known to be free of side-effects.)</p> - <p>Example 2:</p> - <code type="none"> - OnlyOne = is_atom(L) orelse - (is_list(L) andalso length(L) == 1), </code> - </section> -</chapter> - |