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authorBjörn Gustavsson <[email protected]>2015-03-12 15:35:13 +0100
committerBjörn Gustavsson <[email protected]>2015-03-12 17:42:19 +0100
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Update Programming Examples
Language cleaned up by the technical writers xsipewe and tmanevik from Combitech. Proofreading and corrections by Björn Gustavsson.
Diffstat (limited to 'system/doc')
-rw-r--r--system/doc/programming_examples/bit_syntax.xml210
-rw-r--r--system/doc/programming_examples/funs.xmlsrc280
-rw-r--r--system/doc/programming_examples/list_comprehensions.xml86
-rw-r--r--system/doc/programming_examples/part.xml5
-rw-r--r--system/doc/programming_examples/records.xml88
5 files changed, 349 insertions, 320 deletions
diff --git a/system/doc/programming_examples/bit_syntax.xml b/system/doc/programming_examples/bit_syntax.xml
index fb321c1ba9..7ede5b71f9 100644
--- a/system/doc/programming_examples/bit_syntax.xml
+++ b/system/doc/programming_examples/bit_syntax.xml
@@ -31,62 +31,64 @@
<section>
<title>Introduction</title>
- <p>In Erlang a Bin is used for constructing binaries and matching
+ <p>In Erlang, a Bin is used for constructing binaries and matching
binary patterns. A Bin is written with the following syntax:</p>
<code type="none"><![CDATA[
<<E1, E2, ... En>>]]></code>
- <p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is
- to be able to, from a high level, construct a binary,</p>
+ <p>A Bin is a low-level sequence of bits or bytes.
+ The purpose of a Bin is to enable construction of binaries:</p>
<code type="none"><![CDATA[
Bin = <<E1, E2, ... En>>]]></code>
- <p>in which case all elements must be bound, or to match a binary,</p>
+ <p>All elements must be bound. Or match a binary:</p>
<code type="none"><![CDATA[
<<E1, E2, ... En>> = Bin ]]></code>
- <p>where <c>Bin</c> is bound, and where the elements are bound or
+ <p>Here, <c>Bin</c> is bound and the elements are bound or
unbound, as in any match.</p>
- <p>In R12B, a Bin need not consist of a whole number of bytes.</p>
+ <p>Since Erlang R12B, a Bin does not need to consist of a whole number of bytes.</p>
<p>A <em>bitstring</em> is a sequence of zero or more bits, where
- the number of bits doesn't need to be divisible by 8. If the number
+ the number of bits does not need to be divisible by 8. If the number
of bits is divisible by 8, the bitstring is also a binary.</p>
<p>Each element specifies a certain <em>segment</em> of the bitstring.
A segment is a set of contiguous bits of the binary (not
necessarily on a byte boundary). The first element specifies
the initial segment, the second element specifies the following
- segment etc.</p>
- <p>The following examples illustrate how binaries are constructed
+ segment, and so on.</p>
+ <p>The following examples illustrate how binaries are constructed,
or matched, and how elements and tails are specified.</p>
<section>
<title>Examples</title>
- <p><em>Example 1: </em>A binary can be constructed from a set of
+ <p><em>Example 1:</em> A binary can be constructed from a set of
constants or a string literal:</p>
<code type="none"><![CDATA[
Bin11 = <<1, 17, 42>>,
Bin12 = <<"abc">>]]></code>
- <p>yields binaries of size 3; <c>binary_to_list(Bin11)</c>
- evaluates to <c>[1, 17, 42]</c>, and
- <c>binary_to_list(Bin12)</c> evaluates to <c>[97, 98, 99]</c>.</p>
- <p><em>Example 2: </em>Similarly, a binary can be constructed
+ <p>This gives two binaries of size 3, with the following evaluations:</p>
+ <list type="bulleted">
+ <item><c>binary_to_list(Bin11)</c> evaluates to <c>[1, 17, 42]</c>.</item>
+ <item><c>binary_to_list(Bin12)</c> evaluates to <c>[97, 98, 99]</c>.</item>
+ </list>
+ <p><em>Example 2:</em>Similarly, a binary can be constructed
from a set of bound variables:</p>
<code type="none"><![CDATA[
A = 1, B = 17, C = 42,
Bin2 = <<A, B, C:16>>]]></code>
- <p>yields a binary of size 4, and <c>binary_to_list(Bin2)</c>
- evaluates to <c>[1, 17, 00, 42]</c> too. Here we used a
- <em>size expression</em> for the variable <c>C</c> in order to
+ <p>This gives a binary of size 4.
+ Here, a <em>size expression</em> is used for the variable <c>C</c> to
specify a 16-bits segment of <c>Bin2</c>.</p>
- <p><em>Example 3: </em>A Bin can also be used for matching: if
+ <p><c>binary_to_list(Bin2)</c> evaluates to <c>[1, 17, 00, 42]</c>.</p>
+ <p><em>Example 3:</em> A Bin can also be used for matching.
<c>D</c>, <c>E</c>, and <c>F</c> are unbound variables, and
- <c>Bin2</c> is bound as in the former example,</p>
+ <c>Bin2</c> is bound, as in Example 2:</p>
<code type="none"><![CDATA[
<<D:16, E, F/binary>> = Bin2]]></code>
- <p>yields <c>D = 273</c>, <c>E = 00</c>, and F binds to a binary
+ <p>This gives <c>D = 273</c>, <c>E = 00</c>, and F binds to a binary
of size 1: <c>binary_to_list(F) = [42]</c>.</p>
<p><em>Example 4:</em> The following is a more elaborate example
- of matching, where <c>Dgram</c> is bound to the consecutive
- bytes of an IP datagram of IP protocol version 4, and where we
- want to extract the header and the data of the datagram:</p>
+ of matching. Here, <c>Dgram</c> is bound to the consecutive
+ bytes of an IP datagram of IP protocol version 4. The ambition is
+ to extract the header and the data of the datagram:</p>
<code type="none"><![CDATA[
-define(IP_VERSION, 4).
-define(IP_MIN_HDR_LEN, 5).
@@ -102,53 +104,59 @@ case Dgram of
<<Opts:OptsLen/binary,Data/binary>> = RestDgram,
...
end.]]></code>
- <p>Here the segment corresponding to the <c>Opts</c> variable
- has a <em>type modifier</em> specifying that <c>Opts</c> should
+ <p>Here, the segment corresponding to the <c>Opts</c> variable
+ has a <em>type modifier</em>, specifying that <c>Opts</c> is to
bind to a binary. All other variables have the default type
equal to unsigned integer.</p>
- <p>An IP datagram header is of variable length, and its length -
- measured in the number of 32-bit words - is given in
- the segment corresponding to <c>HLen</c>, the minimum value of
- which is 5. It is the segment corresponding to <c>Opts</c>
- that is variable: if <c>HLen</c> is equal to 5, <c>Opts</c>
- will be an empty binary.</p>
+ <p>An IP datagram header is of variable length. This length is
+ measured in the number of 32-bit words and is given in
+ the segment corresponding to <c>HLen</c>. The minimum value of
+ <c>HLen</c> is 5. It is the segment corresponding to <c>Opts</c>
+ that is variable, so if <c>HLen</c> is equal to 5, <c>Opts</c>
+ becomes an empty binary.</p>
<p>The tail variables <c>RestDgram</c> and <c>Data</c> bind to
- binaries, as all tail variables do. Both may bind to empty
+ binaries, as all tail variables do. Both can bind to empty
binaries.</p>
- <p>If the first 4-bits segment of <c>Dgram</c> is not equal to
- 4, or if <c>HLen</c> is less than 5, or if the size of
- <c>Dgram</c> is less than <c>4*HLen</c>, the match of
- <c>Dgram</c> fails.</p>
+ <p>The match of <c>Dgram</c> fails if one of the following occurs:</p>
+ <list type="bulleted">
+ <item>The first 4-bits segment of <c>Dgram</c> is not equal to 4.</item>
+ <item><c>HLen</c> is less than 5.</item>
+ <item>The size of <c>Dgram</c> is less than <c>4*HLen</c>.</item>
+ </list>
</section>
</section>
<section>
- <title>A Lexical Note</title>
- <p>Note that "<c><![CDATA[B=<<1>>]]></c>" will be interpreted as
+ <title>Lexical Note</title>
+ <p>Notice that "<c><![CDATA[B=<<1>>]]></c>" will be interpreted as
"<c><![CDATA[B =< <1>>]]></c>", which is a syntax error.
- The correct way to write the expression is
- "<c><![CDATA[B = <<1>>]]></c>".</p>
+ The correct way to write the expression is:
+ <c><![CDATA[B = <<1>>]]></c>.</p>
</section>
<section>
<title>Segments</title>
<p>Each segment has the following general syntax:</p>
<p><c>Value:Size/TypeSpecifierList</c></p>
- <p>Both the <c>Size</c> and the <c>TypeSpecifier</c> or both may be
- omitted; thus the following variations are allowed:</p>
- <p><c>Value</c></p>
- <p><c>Value:Size</c></p>
- <p><c>Value/TypeSpecifierList</c></p>
- <p>Default values will be used for missing specifications.
- The default values are described in the section
+ <p>The <c>Size</c> or the <c>TypeSpecifier</c>, or both, can be
+ omitted. Thus, the following variants are allowed:</p>
+ <list type="bulleted">
+ <item><c>Value</c></item>
+ <item><c>Value:Size</c></item>
+ <item><c>Value/TypeSpecifierList</c></item>
+ </list>
+ <p>Default values are used when specifications are missing.
+ The default values are described in
<seealso marker="#Defaults">Defaults</seealso>.</p>
- <p>Used in binary construction, the <c>Value</c> part is any
- expression. Used in binary matching, the <c>Value</c> part must
- be a literal or variable. You can read more about
- the <c>Value</c> part in the section about constructing
- binaries and matching binaries.</p>
+ <p>The <c>Value</c> part is any expression, when used in binary construction.
+ Used in binary matching, the <c>Value</c> part must
+ be a literal or a variable. For more information about
+ the <c>Value</c> part, see
+ <seealso marker="#Constructing Binaries and Bitstrings">Constructing Binaries and Bitstrings</seealso>
+ and
+ <seealso marker="#Matching Binaries">Matching Binaries</seealso>.</p>
<p>The <c>Size</c> part of the segment multiplied by the unit in
- the <c>TypeSpecifierList</c> (described below) gives the number
+ <c>TypeSpecifierList</c> (described later) gives the number
of bits for the segment. In construction, <c>Size</c> is any
expression that evaluates to an integer. In matching,
<c>Size</c> must be a constant expression or a variable.</p>
@@ -160,22 +168,22 @@ end.]]></code>
<c>binary</c>.</item>
<tag>Signedness</tag>
<item>The signedness specification can be either <c>signed</c>
- or <c>unsigned</c>. Note that signedness only matters for
+ or <c>unsigned</c>. Notice that signedness only matters for
matching.</item>
<tag>Endianness</tag>
<item>The endianness specification can be either <c>big</c>,
<c>little</c>, or <c>native</c>. Native-endian means that
- the endian will be resolved at load time to be either
+ the endian is resolved at load time, to be either
big-endian or little-endian, depending on what is "native"
for the CPU that the Erlang machine is run on.</item>
<tag>Unit</tag>
<item>The unit size is given as <c>unit:IntegerLiteral</c>.
- The allowed range is 1-256. It will be multiplied by
+ The allowed range is 1-256. It is multiplied by
the <c>Size</c> specifier to give the effective size of
- the segment. In R12B, the unit size specifies the alignment
- for binary segments without size (examples will follow).</item>
+ the segment. Since Erlang R12B, the unit size specifies the alignment
+ for binary segments without size.</item>
</taglist>
- <p>Example:</p>
+ <p><em>Example:</em></p>
<code type="none">
X:4/little-signed-integer-unit:8</code>
<p>This element has a total size of 4*8 = 32 bits, and it contains
@@ -184,13 +192,14 @@ X:4/little-signed-integer-unit:8</code>
<section>
<title>Defaults</title>
- <p><marker id="Defaults"></marker>The default type for a segment is integer. The default
+ <p><marker id="Defaults"></marker>The default type for
+ a segment is integer. The default
type does not depend on the value, even if the value is a
- literal. For instance, the default type in '<c><![CDATA[<<3.14>>]]></c>' is
+ literal. For example, the default type in <c><![CDATA[<<3.14>>]]></c> is
integer, not float.</p>
<p>The default <c>Size</c> depends on the type. For integer it is
8. For float it is 64. For binary it is all of the binary. In
- matching, this default value is only valid for the very last
+ matching, this default value is only valid for the last
element. All other binary elements in matching must have a size
specification.</p>
<p>The default unit depends on the the type. For <c>integer</c>,
@@ -201,61 +210,60 @@ X:4/little-signed-integer-unit:8</code>
<section>
<title>Constructing Binaries and Bitstrings</title>
+ <marker id="Constructing Binaries and Bitstrings"></marker>
<p>This section describes the rules for constructing binaries using
the bit syntax. Unlike when constructing lists or tuples,
the construction of a binary can fail with a <c>badarg</c>
exception.</p>
<p>There can be zero or more segments in a binary to be
- constructed. The expression '<c><![CDATA[<<>>]]></c>' constructs a zero
+ constructed. The expression <c><![CDATA[<<>>]]></c> constructs a zero
length binary.</p>
<p>Each segment in a binary can consist of zero or more bits.
There are no alignment rules for individual segments of type
<c>integer</c> and <c>float</c>. For binaries and bitstrings
without size, the unit specifies the alignment. Since the default
alignment for the <c>binary</c> type is 8, the size of a binary
- segment must be a multiple of 8 bits (i.e. only whole bytes).
- Example:</p>
+ segment must be a multiple of 8 bits, that is, only whole bytes.</p>
+ <p><em>Example:</em></p>
<code type="none"><![CDATA[
<<Bin/binary,Bitstring/bitstring>>]]></code>
<p>The variable <c>Bin</c> must contain a whole number of bytes,
because the <c>binary</c> type defaults to <c>unit:8</c>.
- A <c>badarg</c> exception will be generated if <c>Bin</c> would
- consist of (for instance) 17 bits.</p>
+ A <c>badarg</c> exception is generated if <c>Bin</c>
+ consist of, for example, 17 bits.</p>
- <p>On the other hand, the variable <c>Bitstring</c> may consist of
- any number of bits, for instance 0, 1, 8, 11, 17, 42, and so on,
- because the default <c>unit</c> for bitstrings is 1.</p>
+ <p>The <c>Bitstring</c> variable can consist of
+ any number of bits, for example, 0, 1, 8, 11, 17, 42, and so on.
+ This is because the default <c>unit</c> for bitstrings is 1.</p>
- <warning><p>For clarity, it is recommended not to change the unit
- size for binaries, but to use <c>binary</c> when you need byte
- alignment, and <c>bitstring</c> when you need bit alignment.</p></warning>
+ <p>For clarity, it is recommended not to change the unit
+ size for binaries. Instead, use <c>binary</c> when you need byte alignment
+ and <c>bitstring</c> when you need bit alignment.</p>
- <p>The following example</p>
+ <p>The following example successfully constructs a bitstring of 7 bits,
+ provided that all of X and Y are integers:</p>
<code type="none"><![CDATA[
<<X:1,Y:6>>]]></code>
- <p>will successfully construct a bitstring of 7 bits.
- (Provided that all of X and Y are integers.)</p>
- <p>As noted earlier, segments have the following general syntax:</p>
+ <p>As mentioned earlier, segments have the following general syntax:</p>
<p><c>Value:Size/TypeSpecifierList</c></p>
<p>When constructing binaries, <c>Value</c> and <c>Size</c> can be
any Erlang expression. However, for syntactical reasons, both
<c>Value</c> and <c>Size</c> must be enclosed in parenthesis if
the expression consists of anything more than a single literal
- or variable. The following gives a compiler syntax error:</p>
+ or a variable. The following gives a compiler syntax error:</p>
<code type="none"><![CDATA[
<<X+1:8>>]]></code>
- <p>This expression must be rewritten to</p>
+ <p>This expression must be rewritten into the following,
+ to be accepted by the compiler:</p>
<code type="none"><![CDATA[
<<(X+1):8>>]]></code>
- <p>in order to be accepted by the compiler.</p>
<section>
<title>Including Literal Strings</title>
- <p>As syntactic sugar, an literal string may be written instead
- of a element.</p>
+ <p>A literal string can be written instead of an element:</p>
<code type="none"><![CDATA[
<<"hello">>]]></code>
- <p>which is syntactic sugar for</p>
+ <p>This is syntactic sugar for the following:</p>
<code type="none"><![CDATA[
<<$h,$e,$l,$l,$o>>]]></code>
</section>
@@ -263,29 +271,30 @@ X:4/little-signed-integer-unit:8</code>
<section>
<title>Matching Binaries</title>
- <p>This section describes the rules for matching binaries using
+ <marker id="Matching Binaries"></marker>
+ <p>This section describes the rules for matching binaries, using
the bit syntax.</p>
<p>There can be zero or more segments in a binary pattern.
- A binary pattern can occur in every place patterns are allowed,
- also inside other patterns. Binary patterns cannot be nested.</p>
- <p>The pattern '<c><![CDATA[<<>>]]></c>' matches a zero length binary.</p>
- <p>Each segment in a binary can consist of zero or more bits.</p>
- <p>A segment of type <c>binary</c> must have a size evenly
- divisible by 8 (or divisible by the unit size, if the unit size has been changed).</p>
- <p>A segment of type <c>bitstring</c> has no restrictions on the size.</p>
- <p>As noted earlier, segments have the following general syntax:</p>
+ A binary pattern can occur wherever patterns are allowed,
+ including inside other patterns. Binary patterns cannot be nested.
+ The pattern <c><![CDATA[<<>>]]></c> matches a zero length binary.</p>
+ <p>Each segment in a binary can consist of zero or more bits.
+ A segment of type <c>binary</c> must have a size evenly divisible by 8
+ (or divisible by the unit size, if the unit size has been changed).
+ A segment of type <c>bitstring</c> has no restrictions on the size.</p>
+ <p>As mentioned earlier, segments have the following general syntax:</p>
<p><c>Value:Size/TypeSpecifierList</c></p>
- <p>When matching <c>Value</c> value must be either a variable or
- an integer or floating point literal. Expressions are not
+ <p>When matching <c>Value</c>, value must be either a variable or
+ an integer, or a floating point literal. Expressions are not
allowed.</p>
<p><c>Size</c> must be an integer literal, or a previously bound
- variable. Note that the following is not allowed:</p>
+ variable. The following is not allowed:</p>
<code type="none"><![CDATA[
foo(N, <<X:N,T/binary>>) ->
{X,T}.]]></code>
<p>The two occurrences of <c>N</c> are not related. The compiler
will complain that the <c>N</c> in the size field is unbound.</p>
- <p>The correct way to write this example is like this:</p>
+ <p>The correct way to write this example is as follows:</p>
<code type="none"><![CDATA[
foo(N, Bin) ->
<<X:N,T/binary>> = Bin,
@@ -303,14 +312,14 @@ foo(<<A:8,Rest/binary>>) ->]]></code>
without size:</p>
<code type="none"><![CDATA[
foo(<<A:8,Rest/bitstring>>) ->]]></code>
- <p>There is no restriction on the number of bits in the tail.</p>
+ <p>There are no restrictions on the number of bits in the tail.</p>
</section>
</section>
<section>
<title>Appending to a Binary</title>
- <p>In R12B, the following function for creating a binary out of
- a list of triples of integers is now efficient:</p>
+ <p>Since Erlang R12B, the following function for creating a binary out of
+ a list of triples of integers is efficient:</p>
<code type="none"><![CDATA[
triples_to_bin(T) ->
triples_to_bin(T, <<>>).
@@ -321,7 +330,8 @@ triples_to_bin([], Acc) ->
Acc.]]></code>
<p>In previous releases, this function was highly inefficient, because
the binary constructed so far (<c>Acc</c>) was copied in each recursion step.
- That is no longer the case. See the Efficiency Guide for more information.</p>
+ That is no longer the case. For more information, see
+ <seealso marker="doc/efficiency_guide">Efficiency Guide</seealso>.</p>
</section>
</chapter>
diff --git a/system/doc/programming_examples/funs.xmlsrc b/system/doc/programming_examples/funs.xmlsrc
index 7bfac9db8c..e4f5c9c9c9 100644
--- a/system/doc/programming_examples/funs.xmlsrc
+++ b/system/doc/programming_examples/funs.xmlsrc
@@ -30,128 +30,124 @@
</header>
<section>
- <title>Example 1 - map</title>
- <p>If we want to double every element in a list, we could write a
- function named <c>double</c>:</p>
+ <title>map</title>
+ <p>The following function, <c>double</c>, doubles every element in a list:</p>
<code type="none">
double([H|T]) -> [2*H|double(T)];
double([]) -> [].</code>
- <p>This function obviously doubles the argument entered as input
- as follows:</p>
+ <p>Hence, the argument entered as input is doubled as follows:</p>
<pre>
> <input>double([1,2,3,4]).</input>
[2,4,6,8]</pre>
- <p>We now add the function <c>add_one</c>, which adds one to every
+ <p>The following function, <c>add_one</c>, adds one to every
element in a list:</p>
<code type="none">
add_one([H|T]) -> [H+1|add_one(T)];
add_one([]) -> [].</code>
- <p>These functions, <c>double</c> and <c>add_one</c>, have a very
- similar structure. We can exploit this fact and write a function
- <c>map</c> which expresses this similarity:</p>
+ <p>The functions <c>double</c> and <c>add_one</c> have a
+ similar structure. This can be used by writing a function
+ <c>map</c> that expresses this similarity:</p>
<codeinclude file="funs1.erl" tag="%1" type="erl"></codeinclude>
- <p>We can now express the functions <c>double</c> and
- <c>add_one</c> in terms of <c>map</c> as follows:</p>
+ <p>The functions <c>double</c> and <c>add_one</c> can now be expressed
+ in terms of <c>map</c> as follows:</p>
<code type="none">
double(L) -> map(fun(X) -> 2*X end, L).
add_one(L) -> map(fun(X) -> 1 + X end, L).</code>
- <p><c>map(F, List)</c> is a function which takes a function
- <c>F</c> and a list <c>L</c> as arguments and returns the new
- list which is obtained by applying <c>F</c> to each of
+ <p><c>map(F, List)</c> is a function that takes a function
+ <c>F</c> and a list <c>L</c> as arguments and returns a new
+ list, obtained by applying <c>F</c> to each of
the elements in <c>L</c>.</p>
<p>The process of abstracting out the common features of a number
- of different programs is called procedural abstraction.
- Procedural abstraction can be used in order to write several
- different functions which have a similar structure, but differ
- only in some minor detail. This is done as follows:</p>
+ of different programs is called <em>procedural abstraction</em>.
+ Procedural abstraction can be used to write several
+ different functions that have a similar structure, but differ
+ in some minor detail. This is done as follows:</p>
<list type="ordered">
- <item>write one function which represents the common features of
- these functions</item>
- <item>parameterize the difference in terms of functions which
+ <item><em>Step 1.</em> Write one function that represents the common features of
+ these functions.</item>
+ <item><em>Step 2.</em> Parameterize the difference in terms of functions that
are passed as arguments to the common function.</item>
</list>
</section>
<section>
- <title>Example 2 - foreach</title>
- <p>This example illustrates procedural abstraction. Initially, we
- show the following two examples written as conventional
- functions:</p>
- <list type="ordered">
- <item>all elements of a list are printed onto a stream</item>
- <item>a message is broadcast to a list of processes.</item>
- </list>
+ <title>foreach</title>
+ <p>This section illustrates procedural abstraction. Initially,
+ the following two examples are written as conventional
+ functions.</p>
+ <p>This function prints all elements of a list onto a stream:</p>
<code type="none">
print_list(Stream, [H|T]) ->
io:format(Stream, "~p~n", [H]),
print_list(Stream, T);
print_list(Stream, []) ->
true.</code>
+ <p>This function broadcasts a message to a list of processes:</p>
<code type="none">
broadcast(Msg, [Pid|Pids]) ->
Pid ! Msg,
broadcast(Msg, Pids);
broadcast(_, []) ->
true.</code>
- <p>Both these functions have a very similar structure. They both
- iterate over a list doing something to each element in the list.
- The "something" has to be carried round as an extra argument to
- the function which does this.</p>
+ <p>These two functions have a similar structure. They both
+ iterate over a list and do something to each element in the list.
+ The "something" is passed on as an extra argument to
+ the function that does this.</p>
<p>The function <c>foreach</c> expresses this similarity:</p>
<codeinclude file="funs1.erl" tag="%2" type="erl"></codeinclude>
- <p>Using <c>foreach</c>, <c>print_list</c> becomes:</p>
+ <p>Using the function <c>foreach</c>, the function <c>print_list</c> becomes:</p>
<code type="none">
foreach(fun(H) -> io:format(S, "~p~n",[H]) end, L)</code>
- <p><c>broadcast</c> becomes:</p>
+ <p>Using the function <c>foreach</c>, the function <c>broadcast</c> becomes:</p>
<code type="none">
foreach(fun(Pid) -> Pid ! M end, L)</code>
<p><c>foreach</c> is evaluated for its side-effect and not its
value. <c>foreach(Fun ,L)</c> calls <c>Fun(X)</c> for each
element <c>X</c> in <c>L</c> and the processing occurs in
- the order in which the elements were defined in <c>L</c>.
+ the order that the elements were defined in <c>L</c>.
<c>map</c> does not define the order in which its elements are
processed.</p>
</section>
<section>
- <title>The Syntax of Funs</title>
- <p>Funs are written with the syntax:</p>
+ <title>Syntax of Funs</title>
+ <p>Funs are written with the following syntax:</p>
<code type="none">
F = fun (Arg1, Arg2, ... ArgN) ->
...
end</code>
<p>This creates an anonymous function of <c>N</c> arguments and
binds it to the variable <c>F</c>.</p>
- <p>If we have already written a function in the same module and
- wish to pass this function as an argument, we can use
- the following syntax:</p>
+ <p>Another function, <c>FunctionName</c>, written in the same module,
+ can be passed as an argument, using the following syntax:</p>
<code type="none">
F = fun FunctionName/Arity</code>
- <p>With this form of function reference, the function which is
+ <p>With this form of function reference, the function that is
referred to does not need to be exported from the module.</p>
- <p>We can also refer to a function defined in a different module
+ <p>It is also possible to refer to a function defined in a different module,
with the following syntax:</p>
<code type="none">
F = {Module, FunctionName}</code>
<p>In this case, the function must be exported from the module in
question.</p>
- <p>The follow program illustrates the different ways of creating
+ <p>The following program illustrates the different ways of creating
funs:</p>
<codeinclude file="fun_test.erl" tag="%1" type="erl"></codeinclude>
- <p>We can evaluate the fun <c>F</c> with the syntax:</p>
+ <p>The fun <c>F</c> can be evaluated with the following syntax:</p>
<code type="none">
F(Arg1, Arg2, ..., Argn)</code>
<p>To check whether a term is a fun, use the test
- <c>is_function/1</c> in a guard. Example:</p>
+ <c>is_function/1</c> in a guard.</p>
+ <p><em>Example:</em></p>
<code type="none">
f(F, Args) when is_function(F) ->
apply(F, Args);
f(N, _) when is_integer(N) ->
N.</code>
- <p>Funs are a distinct type. The BIFs erlang:fun_info/1,2 can
+ <p>Funs are a distinct type. The BIFs <c>erlang:fun_info/1,2</c> can
be used to retrieve information about a fun, and the BIF
- erlang:fun_to_list/1 returns a textual representation of a fun.
- The check_process_code/2 BIF returns true if the process
+ <c>erlang:fun_to_list/1</c> returns a textual representation of a fun.
+ The <c>check_process_code/2</c> BIF returns <c>true</c> if the process
contains funs that depend on the old version of a module.</p>
<note>
<p>In OTP R5 and earlier releases, funs were represented using
@@ -161,15 +157,15 @@ f(N, _) when is_integer(N) ->
<section>
<title>Variable Bindings Within a Fun</title>
- <p>The scope rules for variables which occur in funs are as
+ <p>The scope rules for variables that occur in funs are as
follows:</p>
<list type="bulleted">
- <item>All variables which occur in the head of a fun are assumed
+ <item>All variables that occur in the head of a fun are assumed
to be "fresh" variables.</item>
- <item>Variables which are defined before the fun, and which
+ <item>Variables that are defined before the fun, and that
occur in function calls or guard tests within the fun, have
the values they had outside the fun.</item>
- <item>No variables may be exported from a fun.</item>
+ <item>Variables cannot be exported from a fun.</item>
</list>
<p>The following examples illustrate these rules:</p>
<code type="none">
@@ -177,12 +173,13 @@ print_list(File, List) ->
{ok, Stream} = file:open(File, write),
foreach(fun(X) -> io:format(Stream,"~p~n",[X]) end, List),
file:close(Stream).</code>
- <p>In the above example, the variable <c>X</c> which is defined in
- the head of the fun is a new variable. The value of the variable
- <c>Stream</c> which is used within within the fun gets its value
+ <p>Here, the variable <c>X</c>, defined in
+ the head of the fun, is a new variable. The variable
+ <c>Stream</c>, which is used within the fun, gets its value
from the <c>file:open</c> line.</p>
- <p>Since any variable which occurs in the head of a fun is
- considered a new variable it would be equally valid to write:</p>
+ <p>As any variable that occurs in the head of a fun is
+ considered a new variable, it is equally valid to write
+ as follows:</p>
<code type="none">
print_list(File, List) ->
{ok, Stream} = file:open(File, write),
@@ -190,21 +187,21 @@ print_list(File, List) ->
io:format(Stream,"~p~n",[File])
end, List),
file:close(Stream).</code>
- <p>In this example, <c>File</c> is used as the new variable
- instead of <c>X</c>. This is rather silly since code in the body
- of the fun cannot refer to the variable <c>File</c> which is
- defined outside the fun. Compiling this example will yield
- the diagnostic:</p>
+ <p>Here, <c>File</c> is used as the new variable
+ instead of <c>X</c>. This is not so wise because code in the fun
+ body cannot refer to the variable <c>File</c>, which is
+ defined outside of the fun. Compiling this example gives
+ the following diagnostic:</p>
<code type="none">
./FileName.erl:Line: Warning: variable 'File'
shadowed in 'lambda head'</code>
- <p>This reminds us that the variable <c>File</c> which is defined
- inside the fun collides with the variable <c>File</c> which is
+ <p>This indicates that the variable <c>File</c>, which is defined
+ inside the fun, collides with the variable <c>File</c>, which is
defined outside the fun.</p>
<p>The rules for importing variables into a fun has the consequence
- that certain pattern matching operations have to be moved into
+ that certain pattern matching operations must be moved into
guard expressions and cannot be written in the head of the fun.
- For example, we might write the following code if we intend
+ For example, you might write the following code if you intend
the first clause of <c>F</c> to be evaluated when the value of
its argument is <c>Y</c>:</p>
<code type="none">
@@ -216,7 +213,7 @@ f(...) ->
...
end, ...)
...</code>
- <p>instead of</p>
+ <p>instead of writng the following code:</p>
<code type="none">
f(...) ->
Y = ...
@@ -229,35 +226,37 @@ f(...) ->
</section>
<section>
- <title>Funs and the Module Lists</title>
+ <title>Funs and Module Lists</title>
<p>The following examples show a dialogue with the Erlang shell.
All the higher order functions discussed are exported from
the module <c>lists</c>.</p>
<section>
<title>map</title>
+ <p><c>map</c> takes a function of one argument and a list of terms:</p>
<codeinclude file="funs1.erl" tag="%1" type="erl"></codeinclude>
- <p><c>map</c> takes a function of one argument and a list of
- terms. It returns the list obtained by applying the function
+ <p>It returns the list obtained by applying the function
to every argument in the list.</p>
+ <p>When a new fun is defined in the shell, the value of the fun
+ is printed as <c><![CDATA[Fun#<erl_eval>]]></c>:</p>
<pre>
> <input>Double = fun(X) -> 2 * X end.</input>
#Fun&lt;erl_eval.6.72228031&gt;
> <input>lists:map(Double, [1,2,3,4,5]).</input>
[2,4,6,8,10]</pre>
- <p>When a new fun is defined in the shell, the value of the Fun
- is printed as <c><![CDATA[Fun#<erl_eval>]]></c>.</p>
+
</section>
<section>
<title>any</title>
- <codeinclude file="funs1.erl" tag="%4" type="erl"></codeinclude>
<p><c>any</c> takes a predicate <c>P</c> of one argument and a
- list of terms. A predicate is a function which returns
- <c>true</c> or <c>false</c>. <c>any</c> is true if there is a
- term <c>X</c> in the list such that <c>P(X)</c> is <c>true</c>.</p>
- <p>We define a predicate <c>Big(X)</c> which is <c>true</c> if
- its argument is greater that 10.</p>
+ list of terms:</p>
+ <codeinclude file="funs1.erl" tag="%4" type="erl"></codeinclude>
+ <p>A predicate is a function that returns <c>true</c> or <c>false</c>.
+ <c>any</c> is <c>true</c> if there is a term <c>X</c> in the list such that
+ <c>P(X)</c> is <c>true</c>.</p>
+ <p>A predicate <c>Big(X)</c> is defined, which is <c>true</c> if
+ its argument is greater that 10:</p>
<pre>
> <input>Big = fun(X) -> if X > 10 -> true; true -> false end end.</input>
#Fun&lt;erl_eval.6.72228031&gt;
@@ -269,9 +268,10 @@ true</pre>
<section>
<title>all</title>
+ <p><c>all</c> has the same arguments as <c>any</c>:</p>
<codeinclude file="funs1.erl" tag="%3" type="erl"></codeinclude>
- <p><c>all</c> has the same arguments as <c>any</c>. It is true
- if the predicate applied to all elements in the list is true.</p>
+ <p>It is <c>true</c>
+ if the predicate applied to all elements in the list is <c>true</c>.</p>
<pre>
> <input>lists:all(Big, [1,2,3,4,12,6]).</input>
false
@@ -281,11 +281,12 @@ true</pre>
<section>
<title>foreach</title>
- <codeinclude file="funs1.erl" tag="%2" type="erl"></codeinclude>
<p><c>foreach</c> takes a function of one argument and a list of
- terms. The function is applied to each argument in the list.
- <c>foreach</c> returns <c>ok</c>. It is used for its
- side-effect only.</p>
+ terms:</p>
+ <codeinclude file="funs1.erl" tag="%2" type="erl"></codeinclude>
+ <p>The function is applied to each argument in the list.
+ <c>foreach</c> returns <c>ok</c>. It is only used for its
+ side-effect:</p>
<pre>
> <input>lists:foreach(fun(X) -> io:format("~w~n",[X]) end, [1,2,3,4]).</input>
1
@@ -297,15 +298,16 @@ ok</pre>
<section>
<title>foldl</title>
- <codeinclude file="funs1.erl" tag="%8" type="erl"></codeinclude>
<p><c>foldl</c> takes a function of two arguments, an
- accumulator and a list. The function is called with two
+ accumulator and a list:</p>
+ <codeinclude file="funs1.erl" tag="%8" type="erl"></codeinclude>
+ <p>The function is called with two
arguments. The first argument is the successive elements in
- the list, the second argument is the accumulator. The function
- must return a new accumulator which is used the next time
+ the list. The second argument is the accumulator. The function
+ must return a new accumulator, which is used the next time
the function is called.</p>
- <p>If we have a list of lists <c>L = ["I","like","Erlang"]</c>,
- then we can sum the lengths of all the strings in <c>L</c> as
+ <p>If you have a list of lists <c>L = ["I","like","Erlang"]</c>,
+ then you can sum the lengths of all the strings in <c>L</c> as
follows:</p>
<pre>
> <input>L = ["I","like","Erlang"].</input>
@@ -325,11 +327,11 @@ end</code>
<section>
<title>mapfoldl</title>
+ <p><c>mapfoldl</c> simultaneously maps and folds over a list:</p>
<codeinclude file="funs1.erl" tag="%10" type="erl"></codeinclude>
- <p><c>mapfoldl</c> simultaneously maps and folds over a list.
- The following example shows how to change all letters in
- <c>L</c> to upper case and count them.</p>
- <p>First upcase:</p>
+ <p>The following example shows how to change all letters in
+ <c>L</c> to upper case and then count them.</p>
+ <p>First the change to upper case:</p>
<pre>
> <input>Upcase = fun(X) when $a =&lt; X, X =&lt; $z -> X + $A - $a;</input>
<input>(X) -> X</input>
@@ -344,7 +346,7 @@ end</code>
"ERLANG"
> <input>lists:map(Upcase_word, L).</input>
["I","LIKE","ERLANG"]</pre>
- <p>Now we can do the fold and the map at the same time:</p>
+ <p>Now, the fold and the map can be done at the same time:</p>
<pre>
> <input>lists:mapfoldl(fun(Word, Sum) -></input>
<input>{Upcase_word(Word), Sum + length(Word)}</input>
@@ -354,23 +356,24 @@ end</code>
<section>
<title>filter</title>
- <codeinclude file="funs1.erl" tag="%9" type="erl"></codeinclude>
<p><c>filter</c> takes a predicate of one argument and a list
- and returns all element in the list which satisfy
- the predicate.</p>
+ and returns all elements in the list that satisfy
+ the predicate:</p>
+ <codeinclude file="funs1.erl" tag="%9" type="erl"></codeinclude>
<pre>
> <input>lists:filter(Big, [500,12,2,45,6,7]).</input>
[500,12,45]</pre>
- <p>When we combine maps and filters we can write very succinct
- code. For example, suppose we want to define a set difference
- function. We want to define <c>diff(L1, L2)</c> to be
- the difference between the lists <c>L1</c> and <c>L2</c>.
- This is the list of all elements in L1 which are not contained
- in L2. This code can be written as follows:</p>
+ <p>Combining maps and filters enables writing of very succinct
+ code. For example, to define a set difference
+ function <c>diff(L1, L2)</c> to be
+ the difference between the lists <c>L1</c> and <c>L2</c>,
+ the code can be written as follows:</p>
<code type="none">
diff(L1, L2) ->
filter(fun(X) -> not member(X, L2) end, L1).</code>
- <p>The AND intersection of the list <c>L1</c> and <c>L2</c> is
+ <p>This gives the list of all elements in L1 that are not contained
+ in L2.</p>
+ <p> The AND intersection of the list <c>L1</c> and <c>L2</c> is
also easily defined:</p>
<code type="none">
intersection(L1,L2) -> filter(fun(X) -> member(X,L1) end, L2).</code>
@@ -378,9 +381,9 @@ intersection(L1,L2) -> filter(fun(X) -> member(X,L1) end, L2).</code>
<section>
<title>takewhile</title>
- <codeinclude file="funs1.erl" tag="%5" type="erl"></codeinclude>
<p><c>takewhile(P, L)</c> takes elements <c>X</c> from a list
- <c>L</c> as long as the predicate <c>P(X)</c> is true.</p>
+ <c>L</c> as long as the predicate <c>P(X)</c> is true:</p>
+ <codeinclude file="funs1.erl" tag="%5" type="erl"></codeinclude>
<pre>
> <input>lists:takewhile(Big, [200,500,45,5,3,45,6]).</input>
[200,500,45]</pre>
@@ -388,8 +391,8 @@ intersection(L1,L2) -> filter(fun(X) -> member(X,L1) end, L2).</code>
<section>
<title>dropwhile</title>
+ <p><c>dropwhile</c> is the complement of <c>takewhile</c>:</p>
<codeinclude file="funs1.erl" tag="%6" type="erl"></codeinclude>
- <p><c>dropwhile</c> is the complement of <c>takewhile</c>.</p>
<pre>
> <input>lists:dropwhile(Big, [200,500,45,5,3,45,6]).</input>
[5,3,45,6]</pre>
@@ -397,10 +400,10 @@ intersection(L1,L2) -> filter(fun(X) -> member(X,L1) end, L2).</code>
<section>
<title>splitwith</title>
- <codeinclude file="funs1.erl" tag="%7" type="erl"></codeinclude>
<p><c>splitwith(P, L)</c> splits the list <c>L</c> into the two
- sub-lists <c>{L1, L2}</c>, where <c>L = takewhile(P, L)</c>
- and <c>L2 = dropwhile(P, L)</c>.</p>
+ sublists <c>{L1, L2}</c>, where <c>L = takewhile(P, L)</c>
+ and <c>L2 = dropwhile(P, L)</c>:</p>
+ <codeinclude file="funs1.erl" tag="%7" type="erl"></codeinclude>
<pre>
> <input>lists:splitwith(Big, [200,500,45,5,3,45,6]).</input>
{[200,500,45],[5,3,45,6]}</pre>
@@ -408,17 +411,17 @@ intersection(L1,L2) -> filter(fun(X) -> member(X,L1) end, L2).</code>
</section>
<section>
- <title>Funs Which Return Funs</title>
- <p>So far, this section has only described functions which take
- funs as arguments. It is also possible to write more powerful
- functions which themselves return funs. The following examples
- illustrate these type of functions.</p>
+ <title>Funs Returning Funs</title>
+ <p>So far, only functions that take
+ funs as arguments have been described. More powerful
+ functions, that themselves return funs, can also be written. The following
+ examples illustrate these type of functions.</p>
<section>
<title>Simple Higher Order Functions</title>
- <p><c>Adder(X)</c> is a function which, given <c>X</c>, returns
+ <p><c>Adder(X)</c> is a function that given <c>X</c>, returns
a new function <c>G</c> such that <c>G(K)</c> returns
- <c>K + X</c>.</p>
+ <c>K + X</c>:</p>
<pre>
> <input>Adder = fun(X) -> fun(Y) -> X + Y end end.</input>
#Fun&lt;erl_eval.6.72228031&gt;
@@ -438,7 +441,7 @@ ints_from(N) ->
fun() ->
[N|ints_from(N+1)]
end.</code>
- <p>Then we can proceed as follows:</p>
+ <p>Then proceed as follows:</p>
<pre>
> <input>XX = lazy:ints_from(1).</input>
#Fun&lt;lazy.0.29874839&gt;
@@ -450,7 +453,7 @@ ints_from(N) ->
#Fun&lt;lazy.0.29874839&gt;
> <input>hd(Y()).</input>
2</pre>
- <p>etc. - this is an example of "lazy embedding".</p>
+ <p>And so on. This is an example of "lazy embedding".</p>
</section>
<section>
@@ -459,17 +462,21 @@ ints_from(N) ->
<pre>
Parser(Toks) -> {ok, Tree, Toks1} | fail</pre>
<p><c>Toks</c> is the list of tokens to be parsed. A successful
- parse returns <c>{ok, Tree, Toks1}</c>, where <c>Tree</c> is a
- parse tree and <c>Toks1</c> is a tail of <c>Tree</c> which
- contains symbols encountered after the structure which was
- correctly parsed. Otherwise <c>fail</c> is returned.</p>
- <p>The example which follows illustrates a simple, functional
- parser which parses the grammar:</p>
+ parse returns <c>{ok, Tree, Toks1}</c>.</p>
+ <list type="bulleted">
+ <item><c>Tree</c> is a parse tree.</item>
+ <item><c>Toks1</c> is a tail of <c>Tree</c> that
+ contains symbols encountered after the structure that was
+ correctly parsed.</item>
+ </list>
+ <p>An unsuccessful parse returns <c>fail</c>.</p>
+ <p>The following example illustrates a simple, functional
+ parser that parses the grammar:</p>
<pre>
(a | b) &amp; (c | d)</pre>
<p>The following code defines a function <c>pconst(X)</c> in
- the module <c>funparse</c>, which returns a fun which parses a
- list of tokens.</p>
+ the module <c>funparse</c>, which returns a fun that parses a
+ list of tokens:</p>
<codeinclude file="funparse.erl" tag="%14" type="erl"></codeinclude>
<p>This function can be used as follows:</p>
<pre>
@@ -479,17 +486,18 @@ Parser(Toks) -> {ok, Tree, Toks1} | fail</pre>
{ok,{const,a},[b,c]}
> <input>P1([x,y,z]).</input>
fail</pre>
- <p>Next, we define the two higher order functions <c>pand</c>
- and <c>por</c> which combine primitive parsers to produce more
- complex parsers. Firstly <c>pand</c>:</p>
+ <p>Next, the two higher order functions <c>pand</c>
+ and <c>por</c> are defined. They combine primitive parsers to produce more
+ complex parsers.</p>
+ <p>First <c>pand</c>:</p>
<codeinclude file="funparse.erl" tag="%16" type="erl"></codeinclude>
<p>Given a parser <c>P1</c> for grammar <c>G1</c>, and a parser
<c>P2</c> for grammar <c>G2</c>, <c>pand(P1, P2)</c> returns a
- parser for the grammar which consists of sequences of tokens
- which satisfy <c>G1</c> followed by sequences of tokens which
+ parser for the grammar, which consists of sequences of tokens
+ that satisfy <c>G1</c>, followed by sequences of tokens that
satisfy <c>G2</c>.</p>
<p><c>por(P1, P2)</c> returns a parser for the language
- described by the grammar <c>G1</c> or <c>G2</c>.</p>
+ described by the grammar <c>G1</c> or <c>G2</c>:</p>
<codeinclude file="funparse.erl" tag="%15" type="erl"></codeinclude>
<p>The original problem was to parse the grammar
<c><![CDATA[(a | b) & (c | d)]]></c>. The following code addresses this
@@ -497,7 +505,7 @@ fail</pre>
<codeinclude file="funparse.erl" tag="%13" type="erl"></codeinclude>
<p>The following code adds a parser interface to the grammar:</p>
<codeinclude file="funparse.erl" tag="%12" type="erl"></codeinclude>
- <p>We can test this parser as follows:</p>
+ <p>The parser can be tested as follows:</p>
<pre>
> <input>funparse:parse([a,c]).</input>
{ok,{'and',{'or',1,{const,a}},{'or',1,{const,c}}}}
diff --git a/system/doc/programming_examples/list_comprehensions.xml b/system/doc/programming_examples/list_comprehensions.xml
index d6c8a66e13..5b33b14dea 100644
--- a/system/doc/programming_examples/list_comprehensions.xml
+++ b/system/doc/programming_examples/list_comprehensions.xml
@@ -31,18 +31,15 @@
<section>
<title>Simple Examples</title>
- <p>We start with a simple example:</p>
+ <p>This section starts with a simple example, showing a generator and a filter:</p>
<pre>
> <input>[X || X &lt;- [1,2,a,3,4,b,5,6], X > 3].</input>
[a,4,b,5,6]</pre>
- <p>This should be read as follows:</p>
- <quote>
- <p>The list of X such that X is taken from the list
+ <p>This is read as follows: The list of X such that X is taken from the list
<c>[1,2,a,...]</c> and X is greater than 3.</p>
- </quote>
<p>The notation <c><![CDATA[X <- [1,2,a,...]]]></c> is a generator and
the expression <c>X > 3</c> is a filter.</p>
- <p>An additional filter can be added in order to restrict
+ <p>An additional filter, <c>integer(X)</c>, can be added to restrict
the result to integers:</p>
<pre>
> <input>[X || X &lt;- [1,2,a,3,4,b,5,6], integer(X), X > 3].</input>
@@ -56,7 +53,7 @@
<section>
<title>Quick Sort</title>
- <p>The well known quick sort routine can be written as follows:</p>
+ <p>The well-known quick sort routine can be written as follows:</p>
<code type="none"><![CDATA[
sort([Pivot|T]) ->
sort([ X || X <- T, X < Pivot]) ++
@@ -64,15 +61,20 @@ sort([Pivot|T]) ->
sort([ X || X <- T, X >= Pivot]);
sort([]) -> [].]]></code>
<p>The expression <c><![CDATA[[X || X <- T, X < Pivot]]]></c> is the list of
- all elements in <c>T</c>, which are less than <c>Pivot</c>.</p>
+ all elements in <c>T</c> that are less than <c>Pivot</c>.</p>
<p><c><![CDATA[[X || X <- T, X >= Pivot]]]></c> is the list of all elements in
- <c>T</c>, which are greater or equal to <c>Pivot</c>.</p>
- <p>To sort a list, we isolate the first element in the list and
- split the list into two sub-lists. The first sub-list contains
- all elements which are smaller than the first element in
- the list, the second contains all elements which are greater
- than or equal to the first element in the list. We then sort
- the sub-lists and combine the results.</p>
+ <c>T</c> that are greater than or equal to <c>Pivot</c>.</p>
+ <p>A list sorted as follows:</p>
+ <list type="bulleted">
+ <item>The first element in the list is isolated
+ and the list is split into two sublists.</item>
+ <item>The first sublist contains
+ all elements that are smaller than the first element in
+ the list.</item>
+ <item>The second sublist contains all elements that are greater
+ than, or equal to, the first element in the list.</item>
+ <item>Then the sublists are sorted and the results are combined.</item>
+ </list>
</section>
<section>
@@ -82,10 +84,10 @@ sort([]) -> [].]]></code>
<code type="none"><![CDATA[
perms([]) -> [[]];
perms(L) -> [[H|T] || H <- L, T <- perms(L--[H])].]]></code>
- <p>We take take <c>H</c> from <c>L</c> in all possible ways.
+ <p>This takes <c>H</c> from <c>L</c> in all possible ways.
The result is the set of all lists <c>[H|T]</c>, where <c>T</c>
- is the set of all possible permutations of <c>L</c> with
- <c>H</c> removed.</p>
+ is the set of all possible permutations of <c>L</c>, with
+ <c>H</c> removed:</p>
<pre>
> <input>perms([b,u,g]).</input>
[[b,u,g],[b,g,u],[u,b,g],[u,g,b],[g,b,u],[g,u,b]]</pre>
@@ -97,7 +99,7 @@ perms(L) -> [[H|T] || H <- L, T <- perms(L--[H])].]]></code>
that <c>A**2 + B**2 = C**2</c>.</p>
<p>The function <c>pyth(N)</c> generates a list of all integers
<c>{A,B,C}</c> such that <c>A**2 + B**2 = C**2</c> and where
- the sum of the sides is equal to or less than <c>N</c>.</p>
+ the sum of the sides is equal to, or less than, <c>N</c>:</p>
<code type="none"><![CDATA[
pyth(N) ->
[ {A,B,C} ||
@@ -140,7 +142,7 @@ pyth1(N) ->
</section>
<section>
- <title>Simplifications with List Comprehensions</title>
+ <title>Simplifications With List Comprehensions</title>
<p>As an example, list comprehensions can be used to simplify some
of the functions in <c>lists.erl</c>:</p>
<code type="none"><![CDATA[
@@ -151,45 +153,47 @@ filter(Pred, L) -> [X || X <- L, Pred(X)].]]></code>
<section>
<title>Variable Bindings in List Comprehensions</title>
- <p>The scope rules for variables which occur in list
+ <p>The scope rules for variables that occur in list
comprehensions are as follows:</p>
<list type="bulleted">
- <item>all variables which occur in a generator pattern are
- assumed to be "fresh" variables</item>
- <item>any variables which are defined before the list
- comprehension and which are used in filters have the values
- they had before the list comprehension</item>
- <item>no variables may be exported from a list comprehension.</item>
+ <item>All variables that occur in a generator pattern are
+ assumed to be "fresh" variables.</item>
+ <item>Any variables that are defined before the list
+ comprehension, and that are used in filters, have the values
+ they had before the list comprehension.</item>
+ <item>Variables cannot be exported from a list comprehension.</item>
</list>
- <p>As an example of these rules, suppose we want to write
+ <p>As an example of these rules, suppose you want to write
the function <c>select</c>, which selects certain elements from
- a list of tuples. We might write
+ a list of tuples. Suppose you write
<c><![CDATA[select(X, L) -> [Y || {X, Y} <- L].]]></c> with the intention
- of extracting all tuples from <c>L</c> where the first item is
+ of extracting all tuples from <c>L</c>, where the first item is
<c>X</c>.</p>
- <p>Compiling this yields the following diagnostic:</p>
+ <p>Compiling this gives the following diagnostic:</p>
<code type="none">
./FileName.erl:Line: Warning: variable 'X' shadowed in generate</code>
- <p>This diagnostic warns us that the variable <c>X</c> in
- the pattern is not the same variable as the variable <c>X</c>
- which occurs in the function head.</p>
- <p>Evaluating <c>select</c> yields the following result:</p>
+ <p>This diagnostic warns that the variable <c>X</c> in
+ the pattern is not the same as the variable <c>X</c>
+ that occurs in the function head.</p>
+ <p>Evaluating <c>select</c> gives the following result:</p>
<pre>
> <input>select(b,[{a,1},{b,2},{c,3},{b,7}]).</input>
[1,2,3,7]</pre>
- <p>This result is not what we wanted. To achieve the desired
- effect we must write <c>select</c> as follows:</p>
+ <p>This is not the wanted result. To achieve the desired
+ effect, <c>select</c> must be written as follows:</p>
<code type="none"><![CDATA[
select(X, L) -> [Y || {X1, Y} <- L, X == X1].]]></code>
<p>The generator now contains unbound variables and the test has
- been moved into the filter. This now works as expected:</p>
+ been moved into the filter.</p>
+ <p>This now works as expected:</p>
<pre>
> <input>select(b,[{a,1},{b,2},{c,3},{b,7}]).</input>
[2,7]</pre>
- <p>One consequence of the rules for importing variables into a
+ <p>A consequence of the rules for importing variables into a
list comprehensions is that certain pattern matching operations
- have to be moved into the filters and cannot be written directly
- in the generators. To illustrate this, do not write as follows:</p>
+ must be moved into the filters and cannot be written directly
+ in the generators.</p>
+ <p>To illustrate this, do <em>not</em> write as follows:</p>
<code type="none"><![CDATA[
f(...) ->
Y = ...
diff --git a/system/doc/programming_examples/part.xml b/system/doc/programming_examples/part.xml
index 0bec9b4cf5..9329717ce4 100644
--- a/system/doc/programming_examples/part.xml
+++ b/system/doc/programming_examples/part.xml
@@ -28,8 +28,9 @@
<rev></rev>
</header>
<description>
- <p>This chapter contains examples on using records, funs, list
- comprehensions and the bit syntax.</p>
+ <marker id="programming examples"></marker>
+ <p>This section contains examples on using records, funs, list
+ comprehensions, and the bit syntax.</p>
</description>
<xi:include href="records.xml"/>
<xi:include href="funs.xml"/>
diff --git a/system/doc/programming_examples/records.xml b/system/doc/programming_examples/records.xml
index 58cf136a0b..ffcc05e758 100644
--- a/system/doc/programming_examples/records.xml
+++ b/system/doc/programming_examples/records.xml
@@ -30,37 +30,39 @@
</header>
<section>
- <title>Records vs Tuples</title>
- <p>The main advantage of using records instead of tuples is that
+ <title>Records and Tuples</title>
+ <p>The main advantage of using records rather than tuples is that
fields in a record are accessed by name, whereas fields in a
tuple are accessed by position. To illustrate these differences,
- suppose that we want to represent a person with the tuple
+ suppose that you want to represent a person with the tuple
<c>{Name, Address, Phone}</c>.</p>
- <p>We must remember that the <c>Name</c> field is the first
- element of the tuple, the <c>Address</c> field is the second
- element, and so on, in order to write functions which manipulate
- this data. For example, to extract data from a variable <c>P</c>
- which contains such a tuple we might write the following code
- and then use pattern matching to extract the relevant fields.</p>
+ <p>To write functions that manipulate this data, remember the following:</p>
+ <list type="bulleted">
+ <item>The <c>Name</c> field is the first element of the tuple.</item>
+ <item>The <c>Address</c> field is the second element.</item>
+ <item>The <c>Phone</c> field is the third element.</item>
+ </list>
+ <p>For example, to extract data from a variable <c>P</c>
+ that contains such a tuple, you can write the following code
+ and then use pattern matching to extract the relevant fields:</p>
<code type="none">
Name = element(1, P),
Address = element(2, P),
...</code>
- <p>Code like this is difficult to read and understand and errors
- occur if we get the numbering of the elements in the tuple wrong.
- If we change the data representation by re-ordering the fields,
- or by adding or removing a field, then all references to
- the person tuple, wherever they occur, must be checked and
- possibly modified.</p>
- <p>Records allow us to refer to the fields by name and not
- position. We use a record instead of a tuple to store the data.
- If we write a record definition of the type shown below, we can
- then refer to the fields of the record by name.</p>
+ <p>Such code is difficult to read and understand, and errors
+ occur if the numbering of the elements in the tuple is wrong.
+ If the data representation of the fields is changed, by re-ordering,
+ adding, or removing fields, all references to
+ the person tuple must be checked and possibly modified.</p>
+ <p>Records allow references to the fields by name, instead of by
+ position. In the following example, a record instead of a tuple
+ is used to store the data:</p>
<code type="none">
-record(person, {name, phone, address}).</code>
- <p>For example, if <c>P</c> is now a variable whose value is a
- <c>person</c> record, we can code as follows in order to access
- the name and address fields of the records.</p>
+ <p>This enables references to the fields of the record by name.
+ For example, if <c>P</c> is a variable whose value is a
+ <c>person</c> record, the following code access
+ the name and address fields of the records:</p>
<code type="none">
Name = P#person.name,
Address = P#person.address,
@@ -72,24 +74,25 @@ Address = P#person.address,
<section>
<title>Defining a Record</title>
- <p>This definition of a person will be used in many of
- the examples which follow. It contains three fields, <c>name</c>,
- <c>phone</c> and <c>address</c>. The default values for
+ <p>This following definition of a <c>person</c> is used in several
+ examples in this section. Three fields are included, <c>name</c>,
+ <c>phone</c>, and <c>address</c>. The default values for
<c>name</c> and <c>phone</c> is "" and [], respectively.
The default value for <c>address</c> is the atom
<c>undefined</c>, since no default value is supplied for this
field:</p>
<pre>
-record(person, {name = "", phone = [], address}).</pre>
- <p>We have to define the record in the shell in order to be able
- use the record syntax in the examples:</p>
+ <p>The record must be defined in the shell to enable
+ use of the record syntax in the examples:</p>
<pre>
> <input>rd(person, {name = "", phone = [], address}).</input>
person</pre>
- <p>This is due to the fact that record definitions are available
- at compile time only, not at runtime. See <c>shell(3)</c> for
- details on records in the shell.
- </p>
+ <p>This is because record definitions are only available
+ at compile time, not at runtime. For details on records
+ in the shell, see the
+ <seealso marker="stdlib:shell">shell(3)</seealso>
+ manual page in <c>stdlib</c>.</p>
</section>
<section>
@@ -98,12 +101,12 @@ person</pre>
<pre>
> <input>#person{phone=[0,8,2,3,4,3,1,2], name="Robert"}.</input>
#person{name = "Robert",phone = [0,8,2,3,4,3,1,2],address = undefined}</pre>
- <p>Since the <c>address</c> field was omitted, its default value
+ <p>As the <c>address</c> field was omitted, its default value
is used.</p>
- <p>There is a new feature introduced in Erlang 5.1/OTP R8B,
- with which you can set a value to all fields in a record,
- overriding the defaults in the record specification. The special
- field <c>_</c>, means "all fields not explicitly specified".</p>
+ <p>From Erlang 5.1/OTP R8B, a value to all
+ fields in a record can be set with the special field <c>_</c>.
+ <c>_</c> means "all fields not explicitly specified".</p>
+ <p><em>Example:</em></p>
<pre>
> <input>#person{name = "Jakob", _ = '_'}.</input>
#person{name = "Jakob",phone = '_',address = '_'}</pre>
@@ -114,6 +117,7 @@ person</pre>
<section>
<title>Accessing a Record Field</title>
+ <p>The following example shows how to access a record field:</p>
<pre>
> <input>P = #person{name = "Joe", phone = [0,8,2,3,4,3,1,2]}.</input>
#person{name = "Joe",phone = [0,8,2,3,4,3,1,2],address = undefined}
@@ -123,6 +127,7 @@ person</pre>
<section>
<title>Updating a Record</title>
+ <p>The following example shows how to update a record:</p>
<pre>
> <input>P1 = #person{name="Joe", phone=[1,2,3], address="A street"}.</input>
#person{name = "Joe",phone = [1,2,3],address = "A street"}
@@ -133,7 +138,7 @@ person</pre>
<section>
<title>Type Testing</title>
<p>The following example shows that the guard succeeds if
- <c>P</c> is record of type <c>person</c>.</p>
+ <c>P</c> is record of type <c>person</c>:</p>
<pre>
foo(P) when is_record(P, person) -> a_person;
foo(_) -> not_a_person.</pre>
@@ -141,7 +146,7 @@ foo(_) -> not_a_person.</pre>
<section>
<title>Pattern Matching</title>
- <p>Matching can be used in combination with records as shown in
+ <p>Matching can be used in combination with records, as shown in
the following example:</p>
<pre>
> <input>P3 = #person{name="Joe", phone=[0,0,7], address="A street"}.</input>
@@ -163,7 +168,7 @@ find_phone([], Name) ->
<section>
<title>Nested Records</title>
- <p>The value of a field in a record might be an instance of a
+ <p>The value of a field in a record can be an instance of a
record. Retrieval of nested data can be done stepwise, or in a
single step, as shown in the following example:</p>
<pre>
@@ -173,11 +178,12 @@ find_phone([], Name) ->
demo() ->
P = #person{name= #name{first="Robert",last="Virding"}, phone=123},
First = (P#person.name)#name.first.</pre>
- <p>In this example, <c>demo()</c> evaluates to <c>"Robert"</c>.</p>
+ <p>Here, <c>demo()</c> evaluates to <c>"Robert"</c>.</p>
</section>
<section>
- <title>Example</title>
+ <title>A Longer Example</title>
+ <p>Comments are embedded in the following example:</p>
<pre>
%% File: person.hrl