Add a document with the explanations

assign.apl

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+⍝ simple assignment
+N←3
+
+⍝ special value: ⎕ is stdout
+⎕←'hello world'

compose.apl

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-⍝ compose + and × (dot-free style)
-2 1000(+.×)4 5
-
-⍝ is basically:
-+/2 1000×4 5
-
-⍝ or
-+/(2×4) (1000×5)
+⍝ Doesn't work in GNU APL :(
+(⍴∘⍴) 3 4

contents.md

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+=== Table of contents
+
+<table>
+  <thead>
+    <tr>
+      <td>Filename</td>
+      <td>Symbol</td>
+      <td>Monadic</td>
+      <td>Dyadic</td>
+      <td>Operator <i>(higher-order)</i></td>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>flat-contains (epsilon)</td>
+      <td>∊</td>
+      <td>Enlist</td>
+      <td>Membership</td>
+      <td></td>
+    </tr>
+    <tr>
+      <td>assign (left arrow)</td>
+      <td>←</td>
+      <td></td>
+      <td>←</td>
+      <td></td>
+    </tr>
+    <tr>
+      <td>shaped (rho)</td>
+      <td>⍴</td>
+      <td>Shape-of</td>
+      <td>Reshape</td>
+      <td></td>
+    </tr>
+    <tr>
+      <td>resize (up arrow)</td>
+      <td>↑</td>
+      <td>Roll</td>
+      <td>Deal</td>
+      <td></td>
+    </tr>
+    <tr>
+      <td>rand (question mark)</td>
+      <td>?</td>
+      <td>Roll</td>
+      <td>Deal</td>
+      <td></td>
+    </tr>
+    <tr>
+      <td>function (alpha and omega are the arguments)</td>
+      <td>{ <i>and</i> }</td>
+      <td>⍵ <b>(monadic argument)</b></td>
+      <td>⍺ <b>(dyadic argument)</b></td>
+      <td>function</td>
+    </tr>
+    <tr>
+      <td>compose [<b>Dyalog only???</b>] (jot - higher-order function)</td>
+      <td>∘</td>
+      <td></td>
+      <td></td>
+      <td>monadic compose (e.g.: ⍴∘⍴)</td>
+    </tr>
+    <tr>
+      <td>inner-product (dot)</td>
+      <td>.</td>
+      <td></td>
+      <td></td>
+      <td>inner product (e.g.: +.×)(becomes outer product when composed with jot)</td>
+    </tr>
+    <tr>
+      <td>outer-product (jot/dot - higher-order function)</td>
+      <td>∘. (monadic argument: operator)</td>
+      <td></td>
+      <td></td>
+      <td>outer product (e.g.: ∘.+)</td>
+    </tr>
+  </tbody>
+</table>

flat-contains.apl

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+⍝ monadic: enlist (flatten)
+∊0 ((1 2) (3 4) (5 6))
+
+⍝ dyadic: contains
+⍝ [a] is contained in [b]
+1∊1 2 3
+1 2 4∊1 2 3
+
+⎕←'Matrix'
+⍝ deep contain
+(3 3⍴⍳9)∊⍳5 

inner-product.apl

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+⍝ compose + and × (dot-free style)
+2 1000(+.×)4 5
+
+⍝ is basically:
++/2 1000×4 5
+
+⍝ or
++/(2×4) (1000×5)

rand.apl

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-⍝ rand(1..3), rand(1..4), rand(1..5)
+⍝ monadic: roll
 ?3 4 5
 
 ⍝ just generate dices 25x 1d20
 ?25⍴20
 
 ⍝ how many critical hits? sum of the dies that rolled 20
 ?25⍴20
+
+⍝ dyadic: deal
+⍝ picks ⍺x 1d⍵
+3?1000

resize.apl

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+⍝ monadic: first
+↑ (6 4) 5 0 3
+
+⍝ dyadic: take (zero-pads if ⍺>⍴⍵)
+30↑⍳10

shaped.apl

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+⍝ reshape
 ⎕←5 6⍴ ⍳30 ⍝ outer size=5, inner size=6
            ⍝ range (iota)=30
+
+⍝ shape of
+⍴5 6⍴ ⍳30 ⍝ easy enough, (5 6)
+