Add mixing-symbolic-and-direct-manipulation.md

Author: gregr

mixing-symbolic-and-direct-manipulation.md

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+# Example-based programming that mixes symbolic and direct manipulation
+
+
+## Case study: programming an interactive goban
+
+
+### Draw static content, then generalize
+
+* board
+    * draw background
+    * draw grid lines
+    * listify line rows and columns
+    * parameterize and constrain list sizes (num rows must equal num cols)
+    * parameterize spacing dimensions
+    * draw star points
+    * describe and parameterize star point placement conditions in terms of board size
+* stones
+    * draw colorless base stone
+    * parameterize dimensions
+    * instantiate and draw black and white versions
+* board + stones
+    * instantiate and snap stones of both colors over board intersections
+    * listify these stones/positions
+    * transform list -> dict (pos => stone)
+        * also indicates position uniqueness
+    * parameterize over the stone dict
+    * factor stone absolute position dimensions in terms of intersection position
+    * parameterize over dimension factor
+
+
+### Demonstrate dynamic rules, then generalize
+
+* stone placement
+    * correlate mouse click with appropriate intersection position
+    * if position is not empty, do nothing
+    * otherwise, correlate clicked intersection with stone placement
+* removal
+    * correlate a placed stone with starting a new process
+    * remember stone
+    * identify and remember stone neighbors
+        * if any neighbor is empty, full process ends successfully
+        * for each non-empty neighbor of the same color, recurse
+    * if process does not end successfully before we run out of candidate neighbors to follow, process ends in failure
+        * all remembered stones (those traversed of the same color) are removed
+* capture
+    * correlate stone placement intersection with neighboring intersections
+    * identify neighbors of opposite color
+    * with each opposer, attempt removal process
+    * finally, attempt removal process on newly placed stone
+* playing a move
+    * start a list with empty goban
+    * add new goban formed by placing a stone
+    * generalize as procedure taking history list, stone, and placement position, producing a new history list
+* alternating play
+    * correlate stone placement with color alternation
+* comparing two gobans
+    * compare each corresponding intersection to determine whether all are identical
+* positional super ko
+    * extend play-move procedure by comparing the newly-created goban with all gobans already in the history
+    * if any are identical to the new goban, fail
+    * otherwise, succeed with the new history