Erlang Central

String Interpolation

Revision as of 21:46, 18 August 2006 by Cyberlync (Talk | contribs)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

Problem

You want to create string using a mixture of literals and computed values. For example you want to display the current date is the string "Today's date is "

Solution

Make use of Erlang's generic display procedure and variable argument list. For an easy case (displaying date and time), we can make use of the httpd_util:rfc1123_date function to get a string date, and the built-in concatenation (++) operator to construct the string we want:

1> BBBB = "Today's date and time is " ++ httpd_util:rfc1123_date() ++ ".\n".
"Today's date and time is Fri, 20 Aug 2004 22:03:13 GMT.\n"

Other cases require that you use the generic io_lib formatting functions to create strings with the data you want. For example, we could achive the same result as follows:

1> YEAR=2004.
2004
2> MONTH="Aug".
"Aug"
3> DAY=20.
20
4> DAYSTR="Fri".
"Fri"
5> io:fwrite("~s ~s, ~s ~w ~w.\n", ["Today's date is",
5>      DAYSTR, MONTH, DAY, YEAR]).
Today's date is Fri, Aug 20 2004.

If we wanted to be fancy, we could also use httpd_util:month function to get the correct month name:

6> MNTH=8.
8
7> io:fwrite("~s ~s, ~s ~w ~w\n",                                  
7> ["Today's date is", DAYSTR, httpd_util:month(MNTH), DAY, YEAR]).
Today's date is Fri, Aug 20 2004