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| 169 | + <h1 id="troubleshooting"><a class="header" href="#troubleshooting">Troubleshooting</a></h1> |
| 170 | +<p>A list of often encountered errors and their solutions:</p> |
| 171 | +<ul> |
| 172 | +<li> |
| 173 | +<p><strong>Type error: Couldn't match expected type <code>Signal dom (a,b)</code> with actual type <code>(Signal dom a, Signal dom b)</code></strong>:</p> |
| 174 | +<p>Signals of product types and product types of signals are <strong>isomorphic</strong> due to synchronisity principle, but are not (structurally) equal. |
| 175 | +Tuples are a product type. Use the <code>bundle</code> function to convert from a product type to the signal type. |
| 176 | +So if your code which gives the error looks like:</p> |
| 177 | +<pre><code class="language-haskell">... = f a b (c,d) |
| 178 | +</code></pre> |
| 179 | +<p>add the <code>bundle</code> function like so:</p> |
| 180 | +<pre><code class="language-haskell">... = f a b (bundle (c,d)) |
| 181 | +</code></pre> |
| 182 | +<p>Product types supported by <code>bundle</code> are:</p> |
| 183 | +<ul> |
| 184 | +<li>All tuples up to and including 62-tuples (GHC limit)</li> |
| 185 | +<li>The <code>Vec</code>tor type</li> |
| 186 | +</ul> |
| 187 | +</li> |
| 188 | +<li> |
| 189 | +<p><strong>Type error: Couldn't match expected type <code>(Signal dom a, Signal dom b)</code> with actual type <code>Signal dom (a,b)</code></strong>:</p> |
| 190 | +<p>Product types of signals and signals of product types are <strong>isomorphic</strong> due to synchronicity principle, but are not (structurally) equal. |
| 191 | +Tuples are a product type. Use the <code>unbundle</code> function to convert from a signal type to the product type. |
| 192 | +So if your code which gives the error looks like:</p> |
| 193 | +<pre><code class="language-haskell">(c,d) = f a b |
| 194 | +</code></pre> |
| 195 | +<p>add the <code>unbundle</code> function like so:</p> |
| 196 | +<pre><code class="language-haskell">(c,d) = unbundle (f a b) |
| 197 | +</code></pre> |
| 198 | +<p>Product types supported by <code>unbundle</code> are:</p> |
| 199 | +<ul> |
| 200 | +<li>All tuples up to and including 62-tuples (GHC limit)</li> |
| 201 | +<li>The <code>Vec</code>tor type</li> |
| 202 | +</ul> |
| 203 | +</li> |
| 204 | +<li> |
| 205 | +<p><strong>Clash.Netlist(..): Not in normal form: <REASON>: <EXPR></strong>:</p> |
| 206 | +<p>A function could not be transformed into the expected normal form. |
| 207 | +This usually means one of the following:</p> |
| 208 | +<ul> |
| 209 | +<li>The <code>topEntity</code> has higher-order arguments, or a higher-order result.</li> |
| 210 | +<li>You are using types which cannot be represented in hardware.</li> |
| 211 | +</ul> |
| 212 | +<p>The solution for all the above listed reasons is quite simple: remove them. |
| 213 | +That is, make sure that the <code>topEntity</code> is completely monomorphic and first-order. |
| 214 | +Also remove any variables and constants/literals that have a non-representable type; see <a href="limitations.html">Limitations of Clash</a> to find out which types are not representable.</p> |
| 215 | +</li> |
| 216 | +<li> |
| 217 | +<p><strong>Clash.Normalize(..): Clash can only normalize monomorphic functions, but this is polymorphic</strong>:</p> |
| 218 | +<p>If this happens for a <code>topEntity</code> or something with a <code>Synthesize</code> annotation, add a monomorphic type signature. |
| 219 | +Non topEntites should be type-specialized by clash automatically, if not please report this as a bug. |
| 220 | +But adding a monomorphic type signature should still help (when possible).</p> |
| 221 | +</li> |
| 222 | +<li> |
| 223 | +<p><strong>Clash.Normalize(..): Expr belonging to bndr: <FUNCTION> remains recursive after normalization</strong>:</p> |
| 224 | +<ul> |
| 225 | +<li> |
| 226 | +<p>If you actually wrote a recursive function, rewrite it to a non-recursive one using e.g. one of the higher-order functions in <code>Clash.Sized.Vector</code></p> |
| 227 | +</li> |
| 228 | +<li> |
| 229 | +<p>You defined a recursively defined value, but left it polymorphic:</p> |
| 230 | +</li> |
| 231 | +</ul> |
| 232 | +<pre><code class="language-haskell">topEntity x y = acc |
| 233 | + where |
| 234 | + acc = register 3 (acc + x * y) |
| 235 | +</code></pre> |
| 236 | +<p>The above function, works for any number-like type. |
| 237 | +This means that <code>acc</code> is a recursively defined <strong>polymorphic</strong> value. |
| 238 | +Adding a monomorphic type annotation makes the error go away:</p> |
| 239 | +<pre><code class="language-haskell">topEntity |
| 240 | + :: SystemClockResetEnable |
| 241 | + => Signal System (Signed 8) |
| 242 | + -> Signal System (Signed 8) |
| 243 | + -> Signal System (Signed 8) |
| 244 | +topEntity x y = acc |
| 245 | + where |
| 246 | + acc = register 3 (acc + x * y) |
| 247 | +</code></pre> |
| 248 | +</li> |
| 249 | +<li> |
| 250 | +<p><strong>Clash.Normalize.Transformations(..): InlineNonRep: <FUNCTION> already inlined 100 times in:<FUNCTION>, <TYPE></strong>:</p> |
| 251 | +<p>You left the <code>topEntity</code> function polymorphic or higher-order: use <code>:i topEntity</code> to check if the type is indeed polymorphic or higher-order. |
| 252 | +If it is, add a monomorphic type signature, and/or supply higher-order arguments.</p> |
| 253 | +</li> |
| 254 | +<li> |
| 255 | +<p><strong><*** Exception: <<loop>> or "blinking cursor"</strong></p> |
| 256 | +<p>You are using value-recursion, but one of the <code>Vec</code>tor functions that you are using is too <em>strict</em> in one of the recursive arguments. For example:</p> |
| 257 | +<pre><code class="language-haskell">-- Bubble sort for 1 iteration |
| 258 | +sortV xs = map fst sorted :< (snd (last sorted)) |
| 259 | + where |
| 260 | + lefts = head xs :> map snd (init sorted) |
| 261 | + rights = tail xs |
| 262 | + sorted = zipWith compareSwapL lefts rights |
| 263 | + |
| 264 | +-- Compare and swap |
| 265 | +compareSwapL a b = if a < b then (a,b) else (b,a) |
| 266 | +</code></pre> |
| 267 | +<p>Will not terminate because <code>zipWith</code> is too strict in its second argument.</p> |
| 268 | +<p>In this case, adding <code>lazyV</code> on <code>zipWith</code>s second argument:</p> |
| 269 | +<pre><code class="language-haskell">sortVL xs = map fst sorted :< (snd (last sorted)) |
| 270 | + where |
| 271 | + lefts = head xs :> map snd (init sorted) |
| 272 | + rights = tail xs |
| 273 | + sorted = zipWith compareSwapL (lazyV lefts) rights |
| 274 | +</code></pre> |
| 275 | +<p>Results in a successful computation:</p> |
| 276 | +<pre><code>clashi> sortVL (4 :> 1 :> 2 :> 3 :> Nil) |
| 277 | +1 :> 2 :> 3 :> 4 :> Nil |
| 278 | +</code></pre> |
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