1diff --git a/src/Parser/ParseEngine.ts b/src/Parser/ParseEngine.ts
  2index 6d435b5..3fae5e4 100644
  3--- a/src/Parser/ParseEngine.ts
  4+++ b/src/Parser/ParseEngine.ts
  5@@ -195,13 +195,15 @@ const enum ReduceActions {
  6   AS_ERROR = 19,
  7   TO_NUMBER_NAN_AS_ZERO = 20,
  8   CALL_FUNCTION_LAST_BLANK = 21,
  9-  FIXED_CELL_VAL = 22,
 10-  FIXED_CELL_RANGE_VAL = 23,
 11-  CELL_VALUE = 24,
 12-  CELL_RANGE_VALUE = 25,
 13-  PERCENT = 26,
 14-  START_ARRAY = 27,
 15-  INVERT_NUMBER = 28
 16+  CALL_FUNCTION = 22,
 17+  FIXED_CELL_VAL = 23,
 18+  FIXED_CELL_RANGE_VAL = 24,
 19+  CELL_VALUE = 25,
 20+  CELL_RANGE_VALUE = 26,
 21+  PERCENT = 27,
 22+  START_ARRAY = 28,
 23+  INVERT_NUMBER = 29,
 24+  EXPRESSION = 30
 25 };
 26 
 27 /**
 28@@ -234,9 +236,6 @@ class ReductionPair {
 29 
 30 const enum Tree {
 31   START = 0,
 32-  NUMBER = 1,
 33-  STRING = 2,
 34-  BOOLEAN = 3,
 35   VARIABLE = 4,
 36   ERROR = 5,
 37   FORMULA = 6,
 38@@ -247,7 +246,6 @@ const enum Tree {
 39   CARROT = 11,
 40   AMPERSAND = 12,
 41   PERCENT = 13,
 42-  PERIOD = 14,
 43   LESS_THAN = 15,
 44   GREATER_THAN = 16,
 45   EQUALS = 17,
 46@@ -258,10 +256,11 @@ const enum Tree {
 47   FIXED_CELL_REF = 22,
 48   CELL_RANGE_REF = 23,
 49   FIXED_CELL_RANGE_REF = 24,
 50-  OPEN_ARRAY = 25,
 51-  CLOSE_ARRAY = 26,
 52+  // OPEN_ARRAY = 25,
 53+  // CLOSE_ARRAY = 26,
 54   INVERT_NEXT = 27,
 55-  TERMINATE = 28
 56+  EXPRESSION = 28,
 57+  TERMINATE = 29
 58 }
 59 
 60 /**
 61@@ -274,29 +273,29 @@ const enum Tree {
 62 let productions : Array<ReductionPair> = [];
 63 productions[ReduceActions.NO_ACTION] = null;
 64 productions[ReduceActions.RETURN_LAST] = new ReductionPair(3, 2);
 65-productions[ReduceActions.CALL_VARIABLE] = new ReductionPair(Tree.NUMBER, 1);
 66-productions[ReduceActions.AS_NUMBER] = new ReductionPair(Tree.NUMBER, 1);
 67-productions[ReduceActions.INVERT_NUMBER] = new ReductionPair(Tree.NUMBER, 1);
 68-productions[ReduceActions.AS_STRING] = new ReductionPair(Tree.STRING, 1);
 69+productions[ReduceActions.CALL_VARIABLE] = new ReductionPair(Tree.VARIABLE, 1);
 70+productions[ReduceActions.AS_NUMBER] = new ReductionPair(Tree.VARIABLE, 1);
 71+productions[ReduceActions.INVERT_NUMBER] = new ReductionPair(Tree.VARIABLE, 1);
 72+productions[ReduceActions.AS_STRING] = new ReductionPair(Tree.VARIABLE, 1);
 73 productions[ReduceActions.AMPERSAND] = new ReductionPair(Tree.AMPERSAND, 3);
 74 productions[ReduceActions.EQUALS] = new ReductionPair(Tree.EQUALS, 3);
 75 productions[ReduceActions.PLUS] = new ReductionPair(Tree.PLUS, 3);
 76-productions[ReduceActions.LAST_NUMBER] = new ReductionPair(Tree.NUMBER, 3);
 77-productions[ReduceActions.LTE] = new ReductionPair(Tree.BOOLEAN, 4);
 78-productions[ReduceActions.GTE] = new ReductionPair(Tree.BOOLEAN, 4);
 79-productions[ReduceActions.NOT_EQ] = new ReductionPair(Tree.BOOLEAN, 4);
 80-productions[ReduceActions.GT] = new ReductionPair(Tree.BOOLEAN, 3);
 81-productions[ReduceActions.LT] = new ReductionPair(Tree.BOOLEAN, 3);
 82-productions[ReduceActions.MINUS] = new ReductionPair(Tree.NUMBER, 3);
 83-productions[ReduceActions.MULTIPLY] = new ReductionPair(Tree.NUMBER, 3);
 84-productions[ReduceActions.DIVIDE] = new ReductionPair(Tree.NUMBER, 3);
 85-productions[ReduceActions.TO_POWER] = new ReductionPair(Tree.NUMBER, 3);
 86-productions[ReduceActions.TO_NUMBER_NAN_AS_ZERO] = new ReductionPair(Tree.NUMBER, 2);
 87+productions[ReduceActions.LAST_NUMBER] = new ReductionPair(Tree.VARIABLE, 3);
 88+productions[ReduceActions.LTE] = new ReductionPair(Tree.VARIABLE, 4);
 89+productions[ReduceActions.GTE] = new ReductionPair(Tree.VARIABLE, 4);
 90+productions[ReduceActions.NOT_EQ] = new ReductionPair(Tree.VARIABLE, 4);
 91+productions[ReduceActions.GT] = new ReductionPair(Tree.VARIABLE, 3);
 92+productions[ReduceActions.LT] = new ReductionPair(Tree.VARIABLE, 3);
 93+productions[ReduceActions.MINUS] = new ReductionPair(Tree.VARIABLE, 3);
 94+productions[ReduceActions.MULTIPLY] = new ReductionPair(Tree.VARIABLE, 3);
 95+productions[ReduceActions.DIVIDE] = new ReductionPair(Tree.VARIABLE, 3);
 96+productions[ReduceActions.TO_POWER] = new ReductionPair(Tree.VARIABLE, 3);
 97+productions[ReduceActions.TO_NUMBER_NAN_AS_ZERO] = new ReductionPair(Tree.VARIABLE, 2);
 98 productions[ReduceActions.FIXED_CELL_VAL] = new ReductionPair(Tree.VARIABLE, 1);
 99 productions[ReduceActions.FIXED_CELL_RANGE_VAL] = new ReductionPair(Tree.VARIABLE, 3);
100 productions[ReduceActions.CELL_VALUE] = new ReductionPair(Tree.VARIABLE, 1);
101 productions[ReduceActions.CELL_RANGE_VALUE] = new ReductionPair(Tree.VARIABLE, 3);
102-productions[ReduceActions.PERCENT] = new ReductionPair(Tree.NUMBER, 3);
103+productions[ReduceActions.PERCENT] = new ReductionPair(Tree.VARIABLE, 3);
104 productions[ReduceActions.AS_ERROR] = new ReductionPair(Tree.ERROR, 1);
105 const PRODUCTIONS = productions;
106 
107@@ -308,72 +307,35 @@ const PRODUCTIONS = productions;
108  */
109 let table = [];
110 // All functions in the spreadsheet start with a 0-token.
111+// `=`
112 table[Tree.START] = ObjectBuilder
113-  .add(Symbol.NUMBER, Tree.NUMBER)
114-  .add(Symbol.STRING, Tree.STRING)
115-  .add(Symbol.BOOLEAN, Tree.BOOLEAN)
116-  .add(Symbol.FORMULA, Tree.FORMULA)
117+  .add(Symbol.VARIABLE, Tree.VARIABLE)
118   .add(Symbol.CELL_REF, [REDUCE, ReduceActions.CELL_VALUE])
119   .add(Symbol.FIXED_CELL_REF, [REDUCE, ReduceActions.FIXED_CELL_VAL])
120   .add(Symbol.OPEN_ARRAY, null) // Start array, push until done? Come back to this one.
121   .add(Symbol.OPEN_PAREN, null)
122   .add(Symbol.PLUS, [SHIFT, ReduceActions.AS_NUMBER]) // If we're starting out, the operator is just the regular number.
123   .add(Symbol.MINUS, [SHIFT, ReduceActions.INVERT_NUMBER]) // If we're starting out, the operator is inverting the next number
124-  // .add(Symbol.PERIOD, null) // removing for now, maybe we can capture this with numbers, idk.
125   .add(Symbol.WHITE_SPACE, Tree.START) // loop back.
126   .add(Symbol.END, Tree.TERMINATE)
127   .build();
128-table[Tree.NUMBER] = ObjectBuilder
129+table[Tree.VARIABLE] = ObjectBuilder
130   .add(Symbol.PLUS, [SHIFT, ReduceActions.PLUS])
131   .add(Symbol.MINUS, [SHIFT, ReduceActions.MINUS])
132   .add(Symbol.ASTERISK, [SHIFT, ReduceActions.AS_NUMBER]) // maybe
133-  .add(Symbol.DIVIDE, [SHIFT, ReduceActions.DIVIDE]) // At this poing in processing we have "X /" but we need the second variable
134+  .add(Symbol.DIVIDE, [SHIFT, ReduceActions.DIVIDE]) // At this point in processing we have "X /" but we need the second variable
135   .add(Symbol.CARROT, [SHIFT, ReduceActions.TO_POWER])
136   .add(Symbol.PERCENT, [REDUCE, ReduceActions.PERCENT])
137   .add(Symbol.AMPERSAND, [SHIFT, ReduceActions.AMPERSAND])
138-  .add(Symbol.GREATER_THAN, [SHIFT, ReduceActions.GT])
139-  .add(Symbol.LESS_THAN, null)
140-  .add(Symbol.EQUALS, null)
141-  .add(Symbol.COMMA, null)
142-  .add(Symbol.CLOSE_PAREN, null)
143-  .add(Symbol.CLOSE_ARRAY, null)
144-  .add(Symbol.WHITE_SPACE, null)
145-  .add(Symbol.END, null)
146-  .build();
147-table[Tree.STRING] = ObjectBuilder
148-  .add(Symbol.PLUS, null)
149-  .add(Symbol.MINUS, null)
150-  .add(Symbol.ASTERISK, null)
151-  .add(Symbol.DIVIDE, null)
152-  .add(Symbol.CARROT, null)
153-  .add(Symbol.PERCENT, null)
154-  .add(Symbol.AMPERSAND, null)
155-  .add(Symbol.GREATER_THAN, null)
156-  .add(Symbol.LESS_THAN, null)
157-  .add(Symbol.EQUALS, null)
158-  .add(Symbol.COMMA, null)
159-  .add(Symbol.CLOSE_PAREN, null)
160-  .add(Symbol.CLOSE_ARRAY, null)
161-  .add(Symbol.WHITE_SPACE, null)
162-  .add(Symbol.END, null)
163-  .build();
164-table[Tree.BOOLEAN] = ObjectBuilder
165-  .add(Symbol.PLUS, null)
166-  .add(Symbol.MINUS, null)
167-  .add(Symbol.ASTERISK, null)
168-  .add(Symbol.DIVIDE, null)
169-  .add(Symbol.CARROT, null)
170-  .add(Symbol.PERCENT, null)
171-  .add(Symbol.AMPERSAND, null)
172-  .add(Symbol.GREATER_THAN, null)
173-  .add(Symbol.LESS_THAN, null)
174-  .add(Symbol.EQUALS, null)
175-  .add(Symbol.COMMA, null)
176-  .add(Symbol.CLOSE_PAREN, null)
177-  .add(Symbol.CLOSE_ARRAY, null)
178-  .add(Symbol.WHITE_SPACE, null)
179-  .add(Symbol.END, null)
180+  .add(Symbol.GREATER_THAN, Tree.GREATER_THAN) // X>__
181+  .add(Symbol.LESS_THAN, Tree.LESS_THAN) // X>__
182+  .add(Symbol.EQUALS, Tree.EQUALS) // X=__
183+  .add(Symbol.COMMA, Tree.COMMA)
184+  .add(Symbol.CLOSE_PAREN, Tree.CLOSE_PAREN)
185+  .add(Symbol.WHITE_SPACE, Tree.VARIABLE)
186+  .add(Symbol.END, Tree.TERMINATE)
187   .build();
188+// TODO: While almost anything can follow an error, we should really just throw the error, right?
189 table[Tree.ERROR] = ObjectBuilder
190   .add(Symbol.PLUS, null)
191   .add(Symbol.MINUS, null)
192@@ -389,17 +351,14 @@ table[Tree.ERROR] = ObjectBuilder
193   .add(Symbol.END, null)
194   .build();
195 table[Tree.FORMULA] = ObjectBuilder
196-  .add(Symbol.NUMBER, null)
197-  .add(Symbol.STRING, null)
198-  .add(Symbol.BOOLEAN, null)
199-  .add(Symbol.FORMULA, null)
200-  .add(Symbol.CELL_REF, null)
201-  .add(Symbol.FIXED_CELL_REF, null)
202-  .add(Symbol.PERIOD, null) // TODO: Do we really need period? Why can't we capture this as a number w/ the rule-regex?
203+  .add(Symbol.VARIABLE, Tree.VARIABLE)
204+  .add(Symbol.FORMULA, Tree.FORMULA)
205+  .add(Symbol.CELL_REF, [REDUCE, ReduceActions.CELL_VALUE])
206+  .add(Symbol.FIXED_CELL_REF, [REDUCE, ReduceActions.FIXED_CELL_VAL])
207   .add(Symbol.ERROR, null)
208-  .add(Symbol.POUND, null)
209   .add(Symbol.PLUS, null)
210   .add(Symbol.MINUS, null)
211+  .add(Symbol.CLOSE_PAREN, [REDUCE, ReduceActions.CALL_FUNCTION])
212   .add(Symbol.OPEN_PAREN, null)
213   .add(Symbol.OPEN_ARRAY, null)
214   .add(Symbol.WHITE_SPACE, null)
215@@ -507,25 +466,9 @@ table[Tree.PERCENT] = ObjectBuilder
216   .add(Symbol.OPEN_ARRAY, null)
217   .add(Symbol.WHITE_SPACE, null)
218   .add(Symbol.END, null)
219-  .build();
220-table[Tree.PERIOD] = ObjectBuilder
221-  .add(Symbol.PLUS, null)
222-  .add(Symbol.MINUS, null)
223-  .add(Symbol.ASTERISK, null)
224-  .add(Symbol.DIVIDE, null)
225-  .add(Symbol.CARROT, null)
226-  .add(Symbol.PERCENT, null)
227-  .add(Symbol.AMPERSAND, null)
228-  .add(Symbol.GREATER_THAN, null)
229-  .add(Symbol.LESS_THAN, null)
230-  .add(Symbol.EQUALS, null)
231-  .add(Symbol.WHITE_SPACE, null)
232-  .add(Symbol.END, null)
233-  .build();
234+  .build();;
235 table[Tree.LESS_THAN] = ObjectBuilder
236-  .add(Symbol.NUMBER, Tree.NUMBER)
237-  .add(Symbol.STRING, null)
238-  .add(Symbol.BOOLEAN, null)
239+  .add(Symbol.VARIABLE, null)
240   .add(Symbol.FORMULA, null)
241   .add(Symbol.CELL_REF, null)
242   .add(Symbol.FIXED_CELL_REF, null)
243@@ -539,9 +482,7 @@ table[Tree.LESS_THAN] = ObjectBuilder
244   .add(Symbol.END, null)
245   .build();
246 table[Tree.GREATER_THAN] = ObjectBuilder
247-  .add(Symbol.NUMBER, Tree.NUMBER)
248-  .add(Symbol.STRING, null)
249-  .add(Symbol.BOOLEAN, null)
250+  .add(Symbol.VARIABLE, Tree.VARIABLE)
251   .add(Symbol.FORMULA, null)
252   .add(Symbol.CELL_REF, null)
253   .add(Symbol.FIXED_CELL_REF, null)
254@@ -555,9 +496,7 @@ table[Tree.GREATER_THAN] = ObjectBuilder
255   .add(Symbol.END, null)
256   .build();;
257 table[Tree.EQUALS] = ObjectBuilder
258-  .add(Symbol.NUMBER, Tree.NUMBER)
259-  .add(Symbol.STRING, null)
260-  .add(Symbol.BOOLEAN, null)
261+  .add(Symbol.VARIABLE, Tree.VARIABLE)
262   .add(Symbol.FORMULA, null)
263   .add(Symbol.CELL_REF, null)
264   .add(Symbol.FIXED_CELL_REF, null)
265@@ -571,9 +510,7 @@ table[Tree.EQUALS] = ObjectBuilder
266   .add(Symbol.END, null)
267   .build();;
268 table[Tree.COMMA] = ObjectBuilder
269-  .add(Symbol.NUMBER, Tree.NUMBER)
270-  .add(Symbol.STRING, null)
271-  .add(Symbol.BOOLEAN, null)
272+  .add(Symbol.VARIABLE, Tree.VARIABLE)
273   .add(Symbol.FORMULA, null)
274   .add(Symbol.CELL_REF, null)
275   .add(Symbol.FIXED_CELL_REF, null)
276@@ -587,9 +524,7 @@ table[Tree.COMMA] = ObjectBuilder
277   .add(Symbol.END, null)
278   .build();
279 table[Tree.OPEN_PAREN] = ObjectBuilder
280-  .add(Symbol.NUMBER, Tree.NUMBER)
281-  .add(Symbol.STRING, null)
282-  .add(Symbol.BOOLEAN, null)
283+  .add(Symbol.VARIABLE, Tree.VARIABLE)
284   .add(Symbol.FORMULA, null)
285   .add(Symbol.CELL_REF, null)
286   .add(Symbol.FIXED_CELL_REF, null)
287@@ -681,35 +616,7 @@ table[Tree.FIXED_CELL_RANGE_REF] = ObjectBuilder
288   .add(Symbol.WHITE_SPACE, null)
289   .add(Symbol.END, null)
290   .build();
291-table[Tree.OPEN_ARRAY] = ObjectBuilder
292-  .add(Symbol.NUMBER, Tree.NUMBER)
293-  .add(Symbol.STRING, null)
294-  .add(Symbol.BOOLEAN, null)
295-  .add(Symbol.FORMULA, null)
296-  .add(Symbol.CELL_REF, null)
297-  .add(Symbol.FIXED_CELL_REF, null)
298-  .add(Symbol.ERROR, null)
299-  .add(Symbol.PLUS, null)
300-  .add(Symbol.MINUS, null)
301-  .add(Symbol.PERIOD, null)
302-  .add(Symbol.OPEN_PAREN, null)
303-  .add(Symbol.OPEN_ARRAY, null)
304-  .add(Symbol.CLOSE_ARRAY, null)
305-  .add(Symbol.WHITE_SPACE, null)
306-  .build();
307-table[Tree.CLOSE_ARRAY] = ObjectBuilder
308-  .add(Symbol.PLUS, null)
309-  .add(Symbol.MINUS, null)
310-  .add(Symbol.ASTERISK, null)
311-  .add(Symbol.DIVIDE, null)
312-  .add(Symbol.PERCENT, null)
313-  .add(Symbol.CARROT, null)
314-  .add(Symbol.COMMA, null)
315-  .add(Symbol.CLOSE_PAREN, null)
316-  .add(Symbol.CLOSE_ARRAY, null)
317-  .add(Symbol.WHITE_SPACE, null)
318-  .add(Symbol.END, null)
319-  .build();
320+table[Tree.EXPRESSION] = null;
321 table[Tree.INVERT_NEXT] = null;
322 
323