diff options
Diffstat (limited to 'system/doc/getting_started')
| -rw-r--r-- | system/doc/getting_started/conc_prog.xml | 46 | ||||
| -rw-r--r-- | system/doc/getting_started/records_macros.xml | 4 | ||||
| -rw-r--r-- | system/doc/getting_started/robustness.xml | 8 | ||||
| -rw-r--r-- | system/doc/getting_started/seq_prog.xml | 190 |
4 files changed, 185 insertions, 63 deletions
diff --git a/system/doc/getting_started/conc_prog.xml b/system/doc/getting_started/conc_prog.xml index e392287ff0..2b64826a93 100644 --- a/system/doc/getting_started/conc_prog.xml +++ b/system/doc/getting_started/conc_prog.xml @@ -95,7 +95,7 @@ goodbye</pre> the second a "goodbye", the first another "hello" and so forth. But where did the <0.63.0> come from? The return value of a function is of course the return value of the last "thing" in - the function. The last thing in the function <c>start</c> is</p> + the function. The last thing in the function <c>start</c> is:</p> <code type="none"> spawn(tut14, say_something, [goodbye, 3]).</code> <p><c>spawn</c> returns a <em>process identifier</em>, or @@ -166,11 +166,11 @@ Pong_PID = spawn(tut15, pong, [])</code> <c>start</c> now creates another process "ping".</p> <code type="none"> spawn(tut15, ping, [3, Pong_PID]),</code> - <p>this process executes</p> + <p>This process executes:</p> <code type="none"> tut15:ping(3, Pong_PID)</code> <p><0.36.0> is the return value from the <c>start</c> function.</p> - <p>The process "pong" now does:</p> + <p>The process "pong" now does:</p> <code type="none"> receive finished -> @@ -235,7 +235,7 @@ Ping_PID ! pong</code> Pid ! Message</code> <p>I.e. <c>Message</c> (any Erlang term) is sent to the process with identity <c>Pid</c>.</p> - <p>After sending the message <c>pong</c>, to the process "ping", + <p>After sending the message <c>pong</c> to the process "ping", "pong" calls the <c>pong</c> function again, which causes it to get back to the <c>receive</c> again and wait for another message. Now let's look at the process "ping". Recall that it was started @@ -253,7 +253,7 @@ Pong_PID ! {ping, self()},</code> <p><c>self()</c> returns the pid of the process which executes <c>self()</c>, in this case the pid of "ping". (Recall the code for "pong", this will land up in the variable <c>Ping_PID</c> in - the <c>receive</c> previously explained).</p> + the <c>receive</c> previously explained.)</p> <p>"Ping" now waits for a reply from "pong":</p> <code type="none"> receive @@ -352,8 +352,8 @@ pong ! {ping, self()},</code> on different computers. Before we do this, there are a few things we need to set up to get this to work. The distributed Erlang implementation provides a basic security mechanism to prevent - unauthorized access to an Erlang system on another computer - (*manual*). Erlang systems which talk to each other must have + unauthorized access to an Erlang system on another computer. + Erlang systems which talk to each other must have the same <em>magic cookie</em>. The easiest way to achieve this is by having a file called <c>.erlang.cookie</c> in your home directory on all machines which on which you are going to run @@ -363,8 +363,8 @@ pong ! {ping, self()},</code> you can safely ignore this and simply create a file called <c>.erlang.cookie</c> in the directory you get to after executing the command <c>cd</c> without any argument). - The <c>.erlang.cookie</c> file should contain on line with - the same atom. For example on Linux or Unix in the OS shell:</p> + The <c>.erlang.cookie</c> file should contain one line with + the same atom. For example, on Linux or Unix in the OS shell:</p> <pre> $ <input>cd</input> $ <input>cat > .erlang.cookie</input> @@ -373,10 +373,10 @@ $ <input>chmod 400 .erlang.cookie</input></pre> <p>The <c>chmod</c> above make the <c>.erlang.cookie</c> file accessible only by the owner of the file. This is a requirement.</p> <p>When you start an Erlang system which is going to talk to other - Erlang systems, you must give it a name, eg: </p> + Erlang systems, you must give it a name, e.g.: </p> <pre> $ <input>erl -sname my_name</input></pre> - <p>We will see more details of this later (*manual*). If you want to + <p>We will see more details of this later. If you want to experiment with distributed Erlang, but you only have one computer to work on, you can start two separate Erlang systems on the same computer but give them different names. Each Erlang @@ -385,7 +385,7 @@ $ <input>erl -sname my_name</input></pre> IP domain and we can use only the first component of the IP address, if we want to use nodes in different domains we use <c>-name</c> instead, but then all IP address must be given in - full (*manual*).</p> + full.)</p> <p>Here is the ping pong example modified to run on two separate nodes:</p> <code type="none"> @@ -538,9 +538,9 @@ ping finished</pre> <p>Before we start, let's note the following:</p> <list type="bulleted"> <item> - <p>This example will just show the message passing logic no + <p>This example will just show the message passing logic - no attempt at all has been made to provide a nice graphical user - interface - this can of course also be done in Erlang - but + interface. This can, of course, also be done in Erlang - but that's another tutorial.</p> </item> <item> @@ -550,8 +550,8 @@ ping finished</pre> tutorial.</p> </item> <item> - <p>The first program we write will contain some inadequacies as - regards handling of nodes which disappear, we will correct + <p>The first program we write will contain some inadequacies + regarding the handling of nodes which disappear. We will correct these in a later version of the program.</p> </item> </list> @@ -571,7 +571,7 @@ ping finished</pre> %%% already logged in at the same node, login will be rejected %%% with a suitable error message. %%% logoff() -%%% Logs off anybody at at node +%%% Logs off anybody at that node %%% message(ToName, Message) %%% sends Message to ToName. Error messages if the user of this %%% function is not logged on or if ToName is not logged on at @@ -734,11 +734,11 @@ await_result() -> <item>copy the compiled code (<c>messenger.beam</c>) to the directory on each computer where you start Erlang.</item> </list> - <p>In the following example of use of this program, I have started + <p>In the following example of use of this program I have started nodes on four different computers, but if you don't have that - many machines available on your network, you could start up + many machines available on your network you could start up several nodes on the same machine.</p> - <p>We start up four Erlang nodes, messenger@super, c1@bilbo, + <p>We start up four Erlang nodes: messenger@super, c1@bilbo, c2@kosken, c3@gollum.</p> <p>First we start up a the server at messenger@super:</p> <pre> @@ -780,19 +780,19 @@ ok receiver_not_found</pre> <p>But this fails as Fred has already logged off.</p> <p>First let's look at some of the new concepts we have introduced.</p> - <p>There are two versions of the <c>server_transfer</c> function, + <p>There are two versions of the <c>server_transfer</c> function: one with four arguments (<c>server_transfer/4</c>) and one with five (<c>server_transfer/5</c>). These are regarded by Erlang as two separate functions.</p> <p>Note how we write the <c>server</c> function so that it calls - itself, <c>server(User_List)</c> and thus creates a loop. + itself, via <c>server(User_List)</c>, and thus creates a loop. The Erlang compiler is "clever" and optimizes the code so that this really is a sort of loop and not a proper function call. But this only works if there is no code after the call, otherwise the compiler will expect the call to return and make a proper function call. This would result in the process getting bigger and bigger for every loop.</p> - <p>We use functions in the <c>lists</c> module. This is a very + <p>We use functions from the <c>lists</c> module. This is a very useful module and a study of the manual page is recommended (<c>erl -man lists</c>). <c>lists:keymember(Key,Position,Lists)</c> looks through a list diff --git a/system/doc/getting_started/records_macros.xml b/system/doc/getting_started/records_macros.xml index 76e3d185fb..73c8ce5c8d 100644 --- a/system/doc/getting_started/records_macros.xml +++ b/system/doc/getting_started/records_macros.xml @@ -97,7 +97,7 @@ %%% with a suitable error message. %%% logoff() -%%% Logs off anybody at at node +%%% Logs off anybody at that node %%% message(ToName, Message) %%% sends Message to ToName. Error messages if the user of this @@ -284,7 +284,7 @@ server_transfer(From, Name, To, Message, User_List) -> the record is referred to. If you leave out a field when creating a record, it will get the value of the atom undefined. (*manual*)</p> <p>Pattern matching with records is very similar to creating - records. For example inside a <c>case</c> or <c>receive</c>:</p> + records. For example, inside a <c>case</c> or <c>receive</c>:</p> <code type="none"> #message_to{to_name=ToName, message=Message} -></code> <p>is the same as:</p> diff --git a/system/doc/getting_started/robustness.xml b/system/doc/getting_started/robustness.xml index 359ea93275..e8fb81d5e8 100644 --- a/system/doc/getting_started/robustness.xml +++ b/system/doc/getting_started/robustness.xml @@ -30,7 +30,7 @@ </header> <p>There are several things which are wrong with the <seealso marker="conc_prog#ex">messenger example</seealso> from - the previous chapter. For example if a node where a user is logged + the previous chapter. For example, if a node where a user is logged on goes down without doing a log off, the user will remain in the server's <c>User_List</c> but the client will disappear thus making it impossible for the user to log on again as the server @@ -214,9 +214,9 @@ Ping received pong</pre> signal to be sent to "pong" which will also terminate.</p> <p>It is possible to modify the default behaviour of a process so that it does not get killed when it receives abnormal exit - signals, but all signals will be turned into normal messages on + signals, but all signals will be turned into normal messages with the format <c>{'EXIT',FromPID,Reason}</c> and added to the end of - the receiving processes message queue. This behaviour is set by:</p> + the receiving process' message queue. This behaviour is set by:</p> <code type="none"> process_flag(trap_exit, true)</code> <p>There are several other process flags, see @@ -289,7 +289,7 @@ pong exiting, got {'EXIT',<3820.39.0>,ping}</pre> %%% already logged in at the same node, login will be rejected %%% with a suitable error message. %%% logoff() -%%% Logs off anybody at at node +%%% Logs off anybody at that node %%% message(ToName, Message) %%% sends Message to ToName. Error messages if the user of this %%% function is not logged on or if ToName is not logged on at diff --git a/system/doc/getting_started/seq_prog.xml b/system/doc/getting_started/seq_prog.xml index 3830a34e5a..699b9487ed 100644 --- a/system/doc/getting_started/seq_prog.xml +++ b/system/doc/getting_started/seq_prog.xml @@ -31,14 +31,14 @@ <section> <title>The Erlang Shell</title> - <p>Most operating systems have a command interpreter or shell, Unix - and Linux have many, Windows has the Command Prompt. Erlang has + <p>Most operating systems have a command interpreter or shell- Unix + and Linux have many, while Windows has the Command Prompt. Erlang has its own shell where you can directly write bits of Erlang code and evaluate (run) them to see what happens (see <seealso marker="stdlib:shell">shell(3)</seealso>). Start the Erlang shell (in Linux or UNIX) by starting a shell or command interpreter in your operating system and typing - <c>erl</c>, you will see something like this.</p> + <c>erl</c>. You will see something like this.</p> <pre> % <input>erl</input> Erlang R15B (erts-5.9.1) [source] [smp:8:8] [rq:8] [async-threads:0] [hipe] [kernel-poll:false] @@ -62,7 +62,7 @@ Eshell V5.9.1 (abort with ^G) (See the chapter <seealso marker="erts:tty">"tty - A command line interface"</seealso> in ERTS User's Guide).</p> <p>(Note: you will find a lot of line numbers given by the shell out of sequence in this tutorial as it was written and the code - tested in several sessions).</p> + tested in several sessions.)</p> <p>Now let's try a more complex calculation.</p> <pre> 2> <input>(42 + 77) * 66 / 3.</input> @@ -115,7 +115,7 @@ double(X) -> entered and there will also be error messages to give you some idea as to what has gone wrong so you can change what you have written and try again.</p> - <p>Now lets run the program.</p> + <p>Now let's run the program.</p> <pre> 4> <input>tut:double(10).</input> 20</pre> @@ -208,7 +208,7 @@ mult(X, Y) -> called variables. Variables must start with a capital letter (see the chapter <seealso marker="doc/reference_manual:expressions">"Variables"</seealso> - in the Erlang Reference Manual). Examples of variable could be + in the Erlang Reference Manual). Examples of variables could be <c>Number</c>, <c>ShoeSize</c>, <c>Age</c> etc.</p> </section> @@ -271,7 +271,7 @@ convert(N, centimeter) -> Consider:</p> <code type="none"> tut2:convert(3, inch).</code> - <p>Does this mean that 3 is in inches? or that 3 is in centimeters + <p>Does this mean that 3 is in inches? Or that 3 is in centimeters and we want to convert it to inches? So Erlang has a way to group things together to make things more understandable. We call these <em>tuples</em>. Tuples are surrounded by "{" and "}".</p> @@ -309,7 +309,7 @@ convert_length({inch, Y}) -> <p>We have shown tuples with two parts above, but tuples can have as many parts as we want and contain any valid Erlang <em>term</em>. For example, to represent the temperature of - various cities of the world we could write</p> + various cities of the world we could write:</p> <code type="none"> {moscow, {c, -10}} {cape_town, {f, 70}} @@ -325,7 +325,7 @@ convert_length({inch, Y}) -> <title>Lists</title> <p>Whereas tuples group things together, we also want to be able to represent lists of things. Lists in Erlang are surrounded by "[" - and "]". For example a list of the temperatures of various cities + and "]". For example, a list of the temperatures of various cities in the world could be:</p> <code type="none"> [{moscow, {c, -10}}, {cape_town, {f, 70}}, {stockholm, {c, -4}}, @@ -345,7 +345,7 @@ convert_length({inch, Y}) -> [2,3,4,5]</pre> <p>We use | to separate the first elements of the list from the rest of the list. (<c>First</c> has got value 1 and - <c>TheRest</c> value [2,3,4,5]).</p> + <c>TheRest</c> value [2,3,4,5].)</p> <p>Another example:</p> <pre> 20> <input>[E1, E2 | R] = [1,2,3,4,5,6,7].</input> @@ -403,7 +403,7 @@ list_length([First | Rest]) -> the remaining elements <c>Rest</c> is 1 + the length of <c>Rest</c>.</p> <p>(Advanced readers only: This is not tail recursive, there is a - better way to write this function).</p> + better way to write this function.)</p> <p>In general we can say we use tuples where we would use "records" or "structs" in other languages and we use lists when we want to represent things which have varying sizes, (i.e. where we would @@ -419,6 +419,129 @@ list_length([First | Rest]) -> </section> <section> + <title>Maps</title> + <p>Maps are a set of key to value associations. These associations + are encapsulated with "#{" and "}". To create an association from + "key" to value 42, we write:</p> +<code type="none"> +> #{ "key" => 42 }. +#{"key" => 42}</code> + <p>We will jump straight into the deep end with an example using some + interesting features.</p> + <p>The following example shows how we calculate alpha blending using + maps to reference color and alpha channels:</p> + <code type="none"> +-module(color). + +-export([new/4, blend/2]). + +-define(is_channel(V), (is_float(V) andalso V >= 0.0 andalso V =< 1.0)). + +new(R,G,B,A) when ?is_channel(R), ?is_channel(G), + ?is_channel(B), ?is_channel(A) -> + #{red => R, green => G, blue => B, alpha => A}. + +blend(Src,Dst) -> + blend(Src,Dst,alpha(Src,Dst)). + +blend(Src,Dst,Alpha) when Alpha > 0.0 -> + Dst#{ + red := red(Src,Dst) / Alpha, + green := green(Src,Dst) / Alpha, + blue := blue(Src,Dst) / Alpha, + alpha := Alpha + }; +blend(_,Dst,_) -> + Dst#{ + red := 0.0, + green := 0.0, + blue := 0.0, + alpha := 0.0 + }. + +alpha(#{alpha := SA}, #{alpha := DA}) -> + SA + DA*(1.0 - SA). + +red(#{red := SV, alpha := SA}, #{red := DV, alpha := DA}) -> + SV*SA + DV*DA*(1.0 - SA). +green(#{green := SV, alpha := SA}, #{green := DV, alpha := DA}) -> + SV*SA + DV*DA*(1.0 - SA). +blue(#{blue := SV, alpha := SA}, #{blue := DV, alpha := DA}) -> + SV*SA + DV*DA*(1.0 - SA).</code> + <p>Compile (file <c>color.erl</c>) and test:</p> + <pre> +> <input>c(color).</input> +{ok,color} +> <input>C1 = color:new(0.3,0.4,0.5,1.0).</input> +#{alpha => 1.0,blue => 0.5,green => 0.4,red => 0.3} +> <input>C2 = color:new(1.0,0.8,0.1,0.3).</input> +#{alpha => 0.3,blue => 0.1,green => 0.8,red => 1.0} +> <input>color:blend(C1,C2).</input> +#{alpha => 1.0,blue => 0.5,green => 0.4,red => 0.3} +> <input>color:blend(C2,C1).</input> +#{alpha => 1.0,blue => 0.38,green => 0.52,red => 0.51} +</pre> + <p>This example warrants some explanation:</p> + <code type="none"> +-define(is_channel(V), (is_float(V) andalso V >= 0.0 andalso V =< 1.0)).</code> + <p> + First we define a macro <c>is_channel</c> to help with our guard tests. + This is only here for convenience and to reduce syntax cluttering. + + You can read more about <seealso marker="doc/reference_manual:macros">Macros</seealso> + in the Erlang Reference Manual. + </p> + <code type="none"> +new(R,G,B,A) when ?is_channel(R), ?is_channel(G), + ?is_channel(B), ?is_channel(A) -> + #{red => R, green => G, blue => B, alpha => A}.</code> + <p> + The function <c>new/4</c> creates a new map term with and lets the keys + <c>red</c>, <c>green</c>, <c>blue</c> and <c>alpha</c> be associated + with an initial value. In this case we only allow for float + values between and including 0.0 and 1.0 as ensured by the <c>?is_channel/1</c> macro + for each argument. Only the <c>=></c> operator is allowed when creating a new map. + </p> + <p> + By calling <c>blend/2</c> on any color term created by <c>new/4</c> we can calculate + the resulting color as determined by the two maps terms. + </p> + <p> + The first thing <c>blend/2</c> does is to calculate the resulting alpha channel. + </p> + <code type="none"> +alpha(#{alpha := SA}, #{alpha := DA}) -> + SA + DA*(1.0 - SA).</code> + <p> + We fetch the value associated with key <c>alpha</c> for both arguments using + the <c>:=</c> operator. Any other keys + in the map are ignored, only the key <c>alpha</c> is required and checked for. + </p> + <p>This is also the case for functions <c>red/2</c>, <c>blue/2</c> and <c>green/2</c>.</p> + <code type="none"> +red(#{red := SV, alpha := SA}, #{red := DV, alpha := DA}) -> + SV*SA + DV*DA*(1.0 - SA).</code> + <p> + The difference here is that we check for two keys in each map argument. The other keys + are ignored. + </p> + <p> + Finally we return the resulting color in <c>blend/3</c>. + </p> + <code type="none"> +blend(Src,Dst,Alpha) when Alpha > 0.0 -> + Dst#{ + red := red(Src,Dst) / Alpha, + green := green(Src,Dst) / Alpha, + blue := blue(Src,Dst) / Alpha, + alpha := Alpha + };</code> + <p> + We update the <c>Dst</c> map with new channel values. The syntax for updating an existing key with a new value is done with <c>:=</c> operator. + </p> + </section> + + <section> <title>Standard Modules and Manual Pages</title> <p>Erlang has a lot of standard modules to help you do things. For example, the module <c>io</c> contains a lot of functions to help @@ -450,10 +573,9 @@ http://www.erlang.org/doc/r9b/doc/index.html</code> <section> <title>Writing Output to a Terminal</title> <p>It's nice to be able to do formatted output in these example, so - the next example shows a simple way to use to use - the <c>io:format</c> function. Of course, just like all other - exported functions, you can test the <c>io:format</c> function in - the shell:</p> + the next example shows a simple way to use the <c>io:format</c> + function. Of course, just like all other exported functions, you + can test the <c>io:format</c> function in the shell:</p> <pre> 31> <input>io:format("hello world~n", []).</input> hello world @@ -550,7 +672,7 @@ ok</pre> <p>Now we call <c>format_temps(Rest)</c> with the rest of the list as an argument. This way of doing things is similar to the loop constructs in other languages. (Yes, this is recursion, but don't - let that worry you). So the same <c>format_temps</c> function is + let that worry you.) So the same <c>format_temps</c> function is called again, this time <c>City</c> gets the value <c>{cape_town,{f,70}}</c> and we repeat the same procedure as before. We go on doing this until the list becomes empty, i.e. [], @@ -614,12 +736,12 @@ list_max([Head|Rest], Result_so_far) -> the next part of the function.</p> <p>Some useful operators in guards are, < less than, > greater than, == equal, >= greater or equal, =< less or - equal, /= not equal. (see the chapter - <seealso marker="doc/reference_manual:expressions">"Guard Sequences"</seealso> in the Erlang Reference Manual).</p> + equal, /= not equal. (See the chapter + <seealso marker="doc/reference_manual:expressions">"Guard Sequences"</seealso> in the Erlang Reference Manual.)</p> <p>To change the above program to one which works out the minimum value of the element in a list, all we would need to do is to write < instead of >. (But it would be wise to change - the name of the function to <c>list_min</c> :-).</p> + the name of the function to <c>list_min</c> :-).)</p> <p>Remember that I mentioned earlier that a variable could only be given a value once in its scope? In the above we see, for example, that <c>Result_so_far</c> has been given several values. This is @@ -723,7 +845,7 @@ reverse([], [3,2,1]) => write a list manipulating function it is a good idea to check that one isn't already written for you. (see <seealso marker="stdlib:lists">lists(3)</seealso>).</p> - <p>Now lets get back to the cities and temperatures, but take a more + <p>Now let's get back to the cities and temperatures, but take a more structured approach this time. First let's convert the whole list to Celsius as follows and test the function:</p> <code type="none"> @@ -767,7 +889,7 @@ format_temps(List_of_cities) -> <code type="none"> [City | convert_list_to_c(Rest)];</code> <p>We go on doing this until we get to the end of the list (i.e. - the list is empty:</p> + the list is empty):</p> <code type="none"> convert_list_to_c([]) -> [].</code> @@ -1029,13 +1151,13 @@ month_length(Year, Month) -> <section> <title>Built In Functions (BIFs)</title> - <p>Built in functions BIFs are functions which for some reason is + <p>Built in functions (BIFs) are functions which for some reason are built in to the Erlang virtual machine. BIFs often implement functionality that is impossible to implement in Erlang or is too inefficient to implement in Erlang. Some BIFs can be called - by use of the function name only but they are by default belonging - to the erlang module so for example the call to the BIF <c>trunc</c> - below is equivalent with a call to <c>erlang:trunc</c>.</p> + by use of the function name only, but they by default belong + to the erlang module. So for example, the call to the BIF <c>trunc</c> + below is equivalent to a call to <c>erlang:trunc</c>.</p> <p>As you can see, we first find out if a year is leap or not. If a year is divisible by 400, it is a leap year. To find this out we first divide the year by 400 and use the built in function @@ -1052,23 +1174,23 @@ trunc(5.01) = 5 2000 / 400 = 5.0 trunc(5.0) = 5 5 * 400 = 2000</code> - <p>so we have a leap year. The next two tests if the year is - divisible by 100 or 4 are done in the same way. The first - <c>if</c> returns <c>leap</c> or <c>not_leap</c> which lands up + <p>so we have a leap year. The next two tests, which check if the year is + divisible by 100 or 4, are done in the same way. The first + <c>if</c> returns <c>leap</c> or <c>not_leap</c> which ends up in the variable <c>Leap</c>. We use this variable in the guard for <c>feb</c> in the following <c>case</c> which tells us how long the month is.</p> - <p>This example showed the use of <c>trunc</c>, an easier way would - be to use the Erlang operator <c>rem</c> which gives the remainder + <p>This example showed the use of <c>trunc</c>. An easier way would + be to use the Erlang operator <c>rem</c>, which gives the remainder after division. For example:</p> <pre> 74> <input>2004 rem 400.</input> 4</pre> - <p>so instead of writing</p> + <p>so instead of writing:</p> <code type="none"> trunc(Year / 400) * 400 == Year -> leap;</code> - <p>we could write</p> + <p>we could write:</p> <code type="none"> Year rem 400 == 0 -> leap;</code> @@ -1078,7 +1200,7 @@ Year rem 400 == 0 -> (see the chapter <seealso marker="doc/reference_manual:expressions">"Guard Sequences"</seealso> in the Erlang Reference Manual) (Aside for advanced readers: This is to ensure that guards don't have side - effects). Let's play with a few of these functions in the shell:</p> + effects.) Let's play with a few of these functions in the shell:</p> <pre> 75> <input>trunc(5.6).</input> 5 @@ -1145,7 +1267,7 @@ map(Fun, []) -> #Fun<erl_eval.5.123085357> 89> <input>lists:map(Add_3, [1,2,3]).</input> [4,5,6]</pre> - <p>Now lets print out the temperatures in a list of cities (yet + <p>Now let's print out the temperatures in a list of cities (yet again):</p> <pre> 90> <input>Print_City = fun({City, {X, Temp}}) -> io:format("~-15w ~w ~w~n",</input> |