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MLton
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<h1>EtaExpansion</h1>
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<p>Eta expansion is a simple syntactic change used to work around the
<a href="ValueRestriction">ValueRestriction</a> in <a href="StandardML">Standard ML</a>.</p>
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<p>The eta expansion of an expression <code>e</code> is the expression
<code>fn z =&gt; e z</code>, where <code>z</code> does not occur in <code>e</code>.  This only
makes sense if <code>e</code> denotes a function, i.e. is of arrow type.  Eta
expansion delays the evaluation of <code>e</code> until the function is
applied, and will re-evaluate <code>e</code> each time the function is
applied.</p>
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<p>The name "eta expansion" comes from the eta-conversion rule of the
<a href="LambdaCalculus">lambda calculus</a>.  Expansion refers to the
directionality of the equivalence being used, namely taking <code>e</code> to
<code>fn z =&gt; e z</code> rather than <code>fn z =&gt; e z</code> to <code>e</code> (eta
contraction).</p>
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Last updated Thu Oct 21 15:53:06 2021 -0400 by Matthew Fluet.
<a href="https://github.com/MLton/mlton/commits/master/doc/guide/src/EtaExpansion.adoc">Log</a>
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