<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Hi all,<div><br></div><div>I don’t understand why this code:</div><div><br></div><div>50: instance (IsNat n, RealFloat a) => FFT (RTree n) a where</div><div><br></div><div>is generating this error:</div><div><br></div><div><div style="margin: 0px; font-size: 11px; font-family: Menlo;">fft_test.hs:50:36:</div><div style="margin: 0px; font-size: 11px; font-family: Menlo;"> Illegal instance declaration for ‘FFT (RTree n) a’</div><div style="margin: 0px; font-size: 11px; font-family: Menlo;"> (All instance types must be of the form (T a1 ... an)</div><div style="margin: 0px; font-size: 11px; font-family: Menlo;"> where a1 ... an are *distinct type variables*,</div><div style="margin: 0px; font-size: 11px; font-family: Menlo;"> and each type variable appears at most once in the instance head.</div><div style="margin: 0px; font-size: 11px; font-family: Menlo;"> Use FlexibleInstances if you want to disable this.)</div><div style="margin: 0px; font-size: 11px; font-family: Menlo;"> In the instance declaration for ‘FFT (RTree n) a’</div></div><div><br></div><div>and was hoping someone could help me get it.</div><div><br></div><div>Thanks!</div><div>-db</div><div><br></div></body></html>