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<div>Hi,</div><div><br></div><div>I'm very, very new to Haskell. I am trying to understand the following error, but I'm having a hard time wrapping my head around the whole type system.</div><div><br></div><div>
<div style="height:4px; font-size:4px;"><br></div>
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Stack
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<pre style="white-space:pre!important;font-family:Consolas,Liberation Mono,Menlo,Courier,monospace;padding:0;margin:0;font-size:100%;line-height:inherit;background:transparent;border:0;background:rgb(255, 255, 255);">
<div style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">module</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">Stack</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">(</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">Stack</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 162);">(..)</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">)</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">where</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">import</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">Prelude</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">hiding</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">(</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 162);">head</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">,</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 162);">tail</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">)</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">class</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">Stack</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">s</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">where</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 162);">empty</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">::</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">s</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 162);">isEmpty</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">::</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">s</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">-></span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(109, 121, 222);">Bool</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 162);">cons</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">::</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">s</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">-></span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">-></span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">s</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 162);">head</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">::</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">s</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">-></span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 162);">tail</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">::</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">s</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">-></span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">s</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(49, 132, 149);">a</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">data</span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">ListStack</span> a <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">=</span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">LS</span> [a] <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">deriving</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> (</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">Show</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);">)</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">instance</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">Stack</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">ListStack</span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 255);">where</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span> empty <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">=</span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">LS</span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(88, 92, 246);">[]</span></div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span> isEmpty (<span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">LS</span> s) <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">=</span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(60, 76, 114);">null</span> s</div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span> cons (<span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">LS</span> s) x <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">=</span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">LS</span>(x<span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">:</span>s)</div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(60, 76, 114);">head</span>(<span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">LS</span>(x<span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">:</span>_)) <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">=</span> x</div><div style="font-style: normal; font-variant: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace; color: rgb(0, 0, 0); height: 12px;"><span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(0, 0, 0);"> </span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(60, 76, 114);">tail</span>(<span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">LS</span>(x<span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">:</span>xs)) <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(104, 118, 135);">=</span> <span style="font:normal normal normal normal 12px / normal Monaco, Menlo, "Ubuntu Mono", Consolas, source-code-pro, monospace;color:rgb(197, 6, 11);">LS</span> xs</div></div>
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</div><div><br></div><div><br></div><div>The problem is that when I load this code in the interpreter and write</div><div>>empty</div><div>I get the following error</div><div><br></div><div><interactive>:108:1:</div><div> No instance for (Show (s0 a0)) arising from a use of ‘print’</div><div> The type variables ‘s0’, ‘a0’ are ambiguous</div><div><br></div><div>I mean when I write "LS []" it works just fine. But something is wrong with empty.</div><div><br></div><div><br></div><div>Thanks,<br>Uneeb</div><img align="left" width="0" height="0" style="border:0; width:0px; height:0px;" src="https://track.mixmax.com/api/track/v2/qSG7wIMtVD0xGm24g/gIt92YuwWah12ZAFGanFmLiVWZuVnI/IyZy9mLsxWZrNXYoB0cyVmbul2ZlJmI/?sc=false" alt="">
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