Pangram checker

You are encouraged to solve this task according to the task description, using any language you may know.
A pangram is a sentence that contains all the letters of the English alphabet at least once.

For example:   The quick brown fox jumps over the lazy dog.



Task

Write a function or method to check a sentence to see if it is a   pangram   (or not)   and show its use.



Related tasks

   determine if a string has all the same characters
   determine if a string has all unique characters


include "cowgol.coh";
 
sub pangram(str: [uint8]): (r: uint8) is
    var letters: uint8[26];
    MemZero(&letters[0], 26);
 
    loop
        var chr := [str];
        if chr == 0 then break; end if;
        str := @next str;
        chr := (chr | 32) - 'a';
        if chr >= 26 then continue; end if;
        letters[chr] := letters[chr] | 1;
    end loop;
 
    r := 1;
    chr := 0;
    while chr < 26 loop
        r := r & letters[chr];
        if r == 0 then break; end if;
        chr := chr + 1;
    end loop;
end sub;
 
var yesno: [uint8][] := {": no\n", ": yes\n"};
var test: [uint8][] := {
    "The quick brown fox jumps over the lazy dog.",
    "The five boxing wizards dump quickly."
};
 
var i: @indexof test := 0;
while i < @sizeof test loop
    print(test[i]);
    print(yesno[pangram(test[i])]);
    i := i + 1;
end loop;