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<div><a href="index.html" title="">Macaulay2Doc</a> > <a href="___The_sp__Macaulay2_splanguage.html" title="">The Macaulay2 language</a> > <a href="_printing_spand_spformatting_spfor_spnew_spclasses.html" title="">printing and formatting for new classes</a></div>
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<div><h1>printing and formatting for new classes</h1>
<div>After making a new type, it's desirable to install methods for displaying the instances of the new type in various formats.<table class="examples"><tr><td><pre>i1 : Qu = new Type of List
o1 = Qu
o1 : Type</pre>
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<tr><td><pre>i2 : w = new Qu from {1,-2,0,4}
o2 = {1, -2, 0, 4}
o2 : Qu</pre>
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For example, it's desirable to display the quaternion above so it looks like a quaternion. One way to achieve this is to install first a method for creating an <a href="___Expression.html" title="the class of all expressions">Expression</a> from a quaternion, since there are methods already installed for converting expressions to common forms of output, such as to nets, which are used most commonly.<table class="examples"><tr><td><pre>i3 : expression Qu := z -> (
expression z#0 +
expression z#1 * expression "I" +
expression z#2 * expression "J" +
expression z#3 * expression "K");</pre>
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<tr><td><pre>i4 : net Qu := z -> net expression z;</pre>
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<tr><td><pre>i5 : toString Qu := z -> toString expression z;</pre>
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<tr><td><pre>i6 : tex Qu := z -> tex expression z;</pre>
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<tr><td><pre>i7 : html Qu := z -> html expression z;</pre>
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<tr><td><pre>i8 : w
o8 = 1 - 2*I + 4*K
o8 : Qu</pre>
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<tr><td><pre>i9 : toString w
o9 = 1-2*I+4*K</pre>
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<tr><td><pre>i10 : tex w
o10 = $1-2 I+4 K$</pre>
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<tr><td><pre>i11 : html w
o11 = 1-2I+4K</pre>
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Of course, now that we've decided that there should be certain quaternions called <tt>I</tt>, <tt>J</tt>, and <tt>K</tt>, perhaps we should install them, too.<table class="examples"><tr><td><pre>i12 : I = new Qu from {0,1,0,0}
o12 = I
o12 : Qu</pre>
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<tr><td><pre>i13 : J = new Qu from {0,0,1,0}
o13 = J
o13 : Qu</pre>
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<tr><td><pre>i14 : K = new Qu from {0,0,0,1}
o14 = K
o14 : Qu</pre>
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<tr><td><pre>i15 : 2*I + 5*J
o15 = 2*I + 5*J
o15 : Qu</pre>
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<tr><td><pre>i16 : peek oo
o16 = {0, 2, 5, 0}</pre>
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