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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="_making_spnew_spfunctions_spwith_spoptional_sparguments.html" title="">making new functions with optional arguments</a></div>
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<div><h1>making new functions with optional arguments</h1>
<div>Let's consider an example where we wish to construct a linear function of <tt>x</tt> called <tt>f</tt>, with the slope and y-intercept of the graph being optional arguments of <tt>f</tt>. We use the <a href="__gt_gt.html" title="a binary operator, uses include bit shifting, or attaching optional inputs to functions">>></a> operator to attach the default values to our function, coded in a special way.<table class="examples"><tr><td><pre>i1 : opts = {Slope => 1, Intercept => 1}
o1 = {Slope => 1, Intercept => 1}
o1 : List</pre>
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<tr><td><pre>i2 : f = opts >> o -> x -> x * o.Slope + o.Intercept
o2 = f
o2 : FunctionClosure</pre>
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<tr><td><pre>i3 : f 5
o3 = 6</pre>
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<tr><td><pre>i4 : f(5, Slope => 100)
o4 = 501</pre>
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<tr><td><pre>i5 : f(5, Slope => 100, Intercept => 1000)
o5 = 1500</pre>
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In the example the function body is the code <tt>x * opts.Slope + opts.Intercept</tt>. When it is evaluated, a hash table is assigned to <tt>opts</tt>; its keys are the names of the optional arguments, and the values are the corresponding current values, obtained either from the default values specified in the definition of <tt>f</tt>, or from the options specified at the time <tt>f</tt> is called.<p/>
In the example above, the inner function has just one argument, <tt>x</tt>, but handling multiple arguments is just as easy. Here is an example with two arguments.<table class="examples"><tr><td><pre>i6 : f = {a => 1000} >> o -> (x,y) -> x * o.a + y;
--warning: function f redefined</pre>
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<tr><td><pre>i7 : f(3,7)
o7 = 3007</pre>
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<tr><td><pre>i8 : f(5,11,a=>10^20)
o8 = 500000000000000000011</pre>
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