diff --git a/app/imports/parser/functions.js b/app/imports/parser/functions.js
new file mode 100644
index 00000000..57378390
--- /dev/null
+++ b/app/imports/parser/functions.js
@@ -0,0 +1,83 @@
+export default {
+  'abs': {
+    comment: 'Returns the absolute value of a number',
+    examples: [
+      {input: 'abs(9)', result: '9'},
+      {input: 'abs(-3)', result: '3'},
+    ],
+    argumentType: 'number',
+    resultType: 'number',
+    fn: Math.abs,
+  },
+  'sqrt': {
+    comment: 'Returns the square root of a number',
+    examples: [
+      {input: 'sqrt(16)', result: '4'},
+      {input: 'sqrt(10)', result: '3.1622776601683795'},
+    ],
+    argumentType: 'number',
+    resultType: 'number',
+    fn: Math.sqrt,
+  },
+  'max': {
+    comment: 'Returns the largest of the given numbers',
+    examples: [{input: 'min(12, 6, 3, 168)', result: '168'}],
+    argumentType: 'number',
+    resultType: 'number',
+    fn: Math.max,
+  },
+  'min': {
+    comment: 'Returns the smallest of the given numbers',
+    examples: [{input: 'min(12, 6, 3, 168)', result: '3'}],
+    argumentType: 'number',
+    resultType: 'number',
+    fn: Math.min,
+  },
+  'round': {
+    comment: 'Returns the value of a number rounded to the nearest integer',
+    examples: [
+      {input: 'round(5.95)', result: '6'},
+      {input: 'round(5.5)', result: '6'},
+      {input: 'round(5.05)', result: '5'},
+    ],
+    argumentType: 'number',
+    resultType: 'number',
+    fn: Math.round,
+  },
+  'floor': {
+    comment: 'Rounds a number down to the next smallest integer',
+    examples: [
+      {input: 'floor(5.95)', result: '5'},
+      {input: 'floor(5.05)', result: '5'},
+      {input: 'floor(5)', result: '5'},
+      {input: 'floor(-5.5)', result: '-6'},
+    ],
+    argumentType: 'number',
+    resultType: 'number',
+    fn: Math.floor,
+  },
+  'ceil': {
+    comment: 'Rounds a number up to the next largest integer',
+    examples: [
+      {input: 'ceil(5.95)', result: '6'},
+      {input: 'ceil(5.05)', result: '6'},
+      {input: 'ceil(5)', result: '5'},
+      {input: 'ceil(-5.5)', result: '-5'},
+    ],
+    argumentType: 'number',
+    resultType: 'number',
+    fn: Math.ceil,
+  },
+  'trunc': {
+    comment: 'Returns the integer part of a number by removing any fractional digits',
+    examples: [
+      {input: 'trunc(5.95)', result: '5'},
+      {input: 'trunc(5.05)', result: '5'},
+      {input: 'trunc(5)', result: '5'},
+      {input: 'trunc(-5.5)', result: '-5'},
+    ],
+    argumentType: 'number',
+    resultType: 'number',
+    fn: Math.trunc,
+  },
+}
diff --git a/app/imports/parser/parseTree/AccessorNode.js b/app/imports/parser/parseTree/AccessorNode.js
index 2f594e50..f64eb793 100644
--- a/app/imports/parser/parseTree/AccessorNode.js
+++ b/app/imports/parser/parseTree/AccessorNode.js
@@ -27,9 +27,9 @@ export default class AccessorNode extends ParseNode {
     }
   }
   reduce(scope, context){
-    let result = this.compile(scope);
+    let result = this.compile(scope, context);
     if (result instanceof AccessorNode){
-      context.storeError({
+      if (context) context.storeError({
         type: 'info',
         message: `${result.toString()} not found, set to 0`
       });
diff --git a/app/imports/parser/parseTree/CallNode.js b/app/imports/parser/parseTree/CallNode.js
index 31522dfa..3580950b 100644
--- a/app/imports/parser/parseTree/CallNode.js
+++ b/app/imports/parser/parseTree/CallNode.js
@@ -1,6 +1,7 @@
 import ParseNode from '/imports/parser/parseTree/ParseNode.js';
 import ErrorNode from '/imports/parser/parseTree/ErrorNode.js';
 import ConstantNode from '/imports/parser/parseTree/ConstantNode.js';
+import functions from '/imports/parser/functions.js';
 
 export default class CallNode extends ParseNode {
   constructor({functionName, args}) {
@@ -15,7 +16,7 @@ export default class CallNode extends ParseNode {
       error: `${this.functionName} is not a function`,
       context,
     });
-    let args = castArgsToType({fn, scope, args: this.args, type: func.argumentType});
+    let args = castArgsToType({fn, scope, context, args: this.args, type: func.argumentType});
     if (args.failed){
       if (fn === 'reduce'){
         return new ErrorNode({
@@ -51,17 +52,8 @@ export default class CallNode extends ParseNode {
   }
 }
 
-const functions = {
-  'min': {
-    comment: 'Returns the lowest of the given numbers',
-    argumentType: 'number',
-    resultType: 'number',
-    fn: Math.min,
-  },
-}
-
-function castArgsToType({fn, scope, args, type}){
-  let resolvedArgs = args.map(node => node[fn](scope))
+function castArgsToType({fn, scope, context, args, type}){
+  let resolvedArgs = args.map(node => node[fn](scope, context))
   let result = [];
   if (type === 'number'){
     resolvedArgs.forEach(node => {
diff --git a/app/imports/parser/parseTree/IfNode.js b/app/imports/parser/parseTree/IfNode.js
index d088bae7..0224fd0f 100644
--- a/app/imports/parser/parseTree/IfNode.js
+++ b/app/imports/parser/parseTree/IfNode.js
@@ -12,15 +12,15 @@ export default class IfNode extends ParseNode {
     let {condition, consequent, alternative} = this;
     return `${condition.toString()} ? ${consequent.toString()} : ${alternative.toString()}`
   }
-  resolve(fn, scope){
-    let condition = this.condition[fn](scope);
+  resolve(fn, scope, context){
+    let condition = this.condition[fn](scope, context);
     if (condition instanceof ConstantNode){
       if (condition.value){
-        let consequent = this.consequent[fn](scope);
+        let consequent = this.consequent[fn](scope, context);
         consequent.inheritDetails([condition, this]);
         return this.consequent[fn](scope);
       } else {
-        let alternative = this.alternative[fn](scope);
+        let alternative = this.alternative[fn](scope, context);
         alternative.inheritDetails([condition, this]);
         return alternative;
       }
diff --git a/app/imports/parser/parseTree/IndexNode.js b/app/imports/parser/parseTree/IndexNode.js
index 4359ae56..592bf8d0 100644
--- a/app/imports/parser/parseTree/IndexNode.js
+++ b/app/imports/parser/parseTree/IndexNode.js
@@ -6,19 +6,19 @@ export default class IndexNode extends ParseNode {
     this.array = array;
     this.index = index;
   }
-  resolve(fn, scope){
-    let index = this.index[fn](scope);
+  resolve(fn, scope, context){
+    let index = this.index[fn](scope, context);
     if (index.isInteger){
       let selection = this.array.values[index.value - 1];
       if (selection){
-        let result = selection[fn](scope);
+        let result = selection[fn](scope, context);
         result.inheritDetails([index, this]);
         return result;
       }
     }
     return new IndexNode({
-      array: this.array[fn](scope),
-      index: this.index[fn](scope),
+      array: this.array[fn](scope, context),
+      index: this.index[fn](scope, context),
       previousNodes: [this],
     });
   }
diff --git a/app/imports/parser/parseTree/OperatorNode.js b/app/imports/parser/parseTree/OperatorNode.js
index 14935a0f..5fee48c4 100644
--- a/app/imports/parser/parseTree/OperatorNode.js
+++ b/app/imports/parser/parseTree/OperatorNode.js
@@ -9,9 +9,9 @@ export default class OperatorNode extends ParseNode {
     this.fn = fn;
     this.operator = operator;
   }
-  resolve(fn, scope){
-    let leftNode = this.left[fn](scope);
-    let rightNode = this.right[fn](scope);
+  resolve(fn, scope, context){
+    let leftNode = this.left[fn](scope, context);
+    let rightNode = this.right[fn](scope, context);
     let left, right;
     if (leftNode.type !== 'number' || rightNode.type !== 'number'){
       return new OperatorNode({
diff --git a/app/imports/parser/parseTree/ParenthesisNode.js b/app/imports/parser/parseTree/ParenthesisNode.js
index afb8acac..facca06b 100644
--- a/app/imports/parser/parseTree/ParenthesisNode.js
+++ b/app/imports/parser/parseTree/ParenthesisNode.js
@@ -5,8 +5,8 @@ export default class ParenthesisNode extends ParseNode {
 		super(...arguments);
     this.content = content;
   }
-  resolve(fn, scope){
-    let content = this.content[fn](scope);
+  resolve(fn, scope, context){
+    let content = this.content[fn](scope, context);
     if (
       content.constructor.name === 'IfNode' ||
       content.constructor.name === 'OperatorNode'
diff --git a/app/imports/parser/parseTree/RollArrayNode.js b/app/imports/parser/parseTree/RollArrayNode.js
index fe21abd3..978c20d6 100644
--- a/app/imports/parser/parseTree/RollArrayNode.js
+++ b/app/imports/parser/parseTree/RollArrayNode.js
@@ -17,7 +17,6 @@ export default class RollArrayNode extends ParseNode {
     return new ConstantNode({
       value: total,
       type: 'number',
-      previousNodes: [this],
     });
   }
 }
diff --git a/app/imports/parser/parseTree/RollNode.js b/app/imports/parser/parseTree/RollNode.js
index 070ac165..d57bd734 100644
--- a/app/imports/parser/parseTree/RollNode.js
+++ b/app/imports/parser/parseTree/RollNode.js
@@ -8,9 +8,9 @@ export default class RollNode extends ParseNode {
     this.left = left;
     this.right = right;
   }
-  compile(scope){
-    let left = this.left.compile(scope);
-    let right = this.right.compile(scope);
+  compile(scope, context){
+    let left = this.left.compile(scope, context);
+    let right = this.right.compile(scope, context);
     return new RollNode({left, right, previousNodes: [this]});
   }
   toString(){
@@ -23,8 +23,8 @@ export default class RollNode extends ParseNode {
     }
   }
   roll(scope, context){
-    let left = this.left.reduce(scope);
-    let right = this.right.reduce(scope);
+    let left = this.left.reduce(scope, context);
+    let right = this.right.reduce(scope, context);
     if (!left.isInteger){
       return new ErrorNode({
         node: this,
@@ -56,7 +56,7 @@ export default class RollNode extends ParseNode {
     }
     return new RollArrayNode({values});
   }
-  reduce(scope){
-    return this.roll(scope).reduce(scope);
+  reduce(scope, context){
+    return this.roll(scope, context).reduce(scope, context);
   }
 }
diff --git a/app/imports/parser/parseTree/SymbolNode.js b/app/imports/parser/parseTree/SymbolNode.js
index 73becc6f..b65a5523 100644
--- a/app/imports/parser/parseTree/SymbolNode.js
+++ b/app/imports/parser/parseTree/SymbolNode.js
@@ -1,6 +1,5 @@
 import ParseNode from '/imports/parser/parseTree/ParseNode.js';
 import ConstantNode from '/imports/parser/parseTree/ConstantNode.js';
-import ErrorNode from '/imports/parser/parseTree/ErrorNode.js';
 
 export default class SymbolNode extends ParseNode {
   constructor({name}){
@@ -19,23 +18,25 @@ export default class SymbolNode extends ParseNode {
       type = typeof value;
     }
     if (type === 'string' || type === 'number' || type === 'boolean'){
-      return new ConstantNode({value, type, previousNodes: [this]});
+      return new ConstantNode({value, type});
     } else if (type === 'undefined'){
       return new SymbolNode({
         name: this.name,
-        previousNodes: [this],
       });
     } else {
       throw new Meteor.Error(`Unexpected case: ${this.name} resolved to ${value}`);
     }
   }
-  reduce(scope){
+  reduce(scope, context){
     let result = this.compile(scope);
     if (result instanceof SymbolNode){
-      return new ErrorNode({
-        node: result,
-        error: `${this.toString()} could not be resolved`,
-        previousNodes: [result],
+      if (context) context.storeError({
+        type: 'info',
+        message: `${result.toString()} not found, set to 0`
+      });
+      return new ConstantNode({
+        type: 'number',
+        value: 0,
       });
     } else {
       return result;
diff --git a/app/imports/ui/documentation/FunctionReference.vue b/app/imports/ui/documentation/FunctionReference.vue
new file mode 100644
index 00000000..202fa60b
--- /dev/null
+++ b/app/imports/ui/documentation/FunctionReference.vue
@@ -0,0 +1,49 @@
+<template lang="html">
+  <div>
+    <div
+      v-for="fn in functions"
+      :key="fn.name"
+      class="mb-3"
+    >
+      <h3>{{ fn.name }}</h3>
+      <div class="my-2">
+        {{ fn.comment }}
+      </div>
+      <table>
+        <tr
+          v-for="example in fn.examples"
+          :key="example.input"
+        >
+          <td>
+            <code>{{ example.input }}</code>
+          </td>
+          <td>
+            <v-icon>arrow_right_alt</v-icon>
+          </td>
+          <td>
+            <code>{{ example.result }}</code>
+          </td>
+        </tr>
+      </table>
+    </div>
+  </div>
+</template>
+
+<script>
+import functions from '/imports/parser/functions.js';
+export default {
+  computed:{
+    functions(){
+      let fns = [];
+      for (let name in functions){
+        let f = functions[name];
+        fns.push({name, ...f});
+      }
+      return fns;
+    }
+  }
+}
+</script>
+
+<style lang="css" scoped>
+</style>
diff --git a/app/imports/ui/pages/Parser.vue b/app/imports/ui/pages/Parser.vue
index cb3ddd92..74a73945 100644
--- a/app/imports/ui/pages/Parser.vue
+++ b/app/imports/ui/pages/Parser.vue
@@ -2,7 +2,16 @@
   <div class="layout column align-center justify-center pa-4">
     <v-card style="width: 100%; max-width: 400px;">
       <v-card-text>
-        <v-text-field v-model="input" />
+        <v-text-field
+          v-model="input"
+          label="input"
+        />
+        <v-btn
+          icon
+          @click="recompute"
+        >
+          <v-icon>refresh</v-icon>
+        </v-btn>
         <v-textarea
           v-model="output"
           readonly
@@ -33,15 +42,25 @@
           readonly
           label="reduced"
         />
+        <v-textarea
+          :value="contextJSON"
+          readonly
+          label="reduced"
+        />
+        <function-reference />
       </v-card-text>
     </v-card>
   </div>
 </template>
 
 <script>
-import Parser from '/imports/parser/parser.js';
-console.log(Parser);
+import { parse, CompilationContext } from '/imports/parser/parser.js';
+import FunctionReference from '/imports/ui/documentation/FunctionReference.vue';
+console.log(parse);
 export default {
+  components: {
+    FunctionReference,
+  },
   data(){return {
     input: null,
     output: null,
@@ -50,22 +69,35 @@ export default {
     rolled: null,
     reduced: null,
     reducedJson: null,
+    context: null,
   }},
+  computed: {
+    contextJSON(){
+      return JSON.stringify(this.context, null, 2);
+    }
+  },
   watch: {
-    input(val){
+    input(){
+      this.recompute();
+    }
+  },
+  methods: {
+    recompute(){
+      let val = this.input;
       this.output = this.compiled = this.string = '';
-      let output = new Parser().feed(val).finish()[0];
+      let output = parse(val);
       console.log(output);
       this.output = JSON.stringify(output, null, 2);
       if (!output) return;
       this.string = output;
       let scope = {strength: {value: 16}, hitpoints: {value: 32, currentValue: 8}, mouse: 3};
-      this.compiled = output.compile(scope);
-      this.rolled = output.roll(scope);
-      this.reduced = output.reduce(scope);
+      this.context = new CompilationContext();
+      this.compiled = output.compile(scope, this.context);
+      this.rolled = this.compiled.roll(scope, this.context);
+      this.reduced = this.rolled.reduce(scope, this.context);
       this.reducedJson = JSON.stringify(this.reduced, null, 2)
     }
-  },
+  }
 }
 </script>