diff --git a/src/ast.ts b/src/ast.ts
new file mode 100644
index 0000000..d035843
--- /dev/null
+++ b/src/ast.ts
@@ -0,0 +1,38 @@
+export enum RuleType {
+  Name = "Name",
+  Author = "Author",
+  Description = "Description",
+  Warmup = "Warmup",
+  Rest = "Rest",
+  Interval = "Interval",
+  Cooldown = "Cooldown",
+}
+
+export type Rule = {
+  type: RuleType;
+  params: Param[];
+};
+
+export enum ParamType {
+  Text = "Text",
+  Power = "Power",
+  PowerRange = "PowerRange",
+  Cadence = "Cadence",
+  Duration = "Duration",
+}
+
+export type TextParam = { type: ParamType.Text; value: string };
+export type PowerParam = { type: ParamType.Power; value: number };
+export type PowerRangeParam = {
+  type: ParamType.PowerRange;
+  value: [number, number];
+};
+export type CadenceParam = { type: ParamType.Cadence; value: number };
+export type DurationParam = { type: ParamType.Duration; value: number };
+
+export type Param =
+  | TextParam
+  | PowerParam
+  | PowerRangeParam
+  | CadenceParam
+  | DurationParam;
diff --git a/src/index.ts b/src/index.ts
index 9de4c9c..b4fbfe7 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,96 +1,5 @@
 import * as fs from "fs";
-
-enum RuleType {
-  Name = "Name",
-  Author = "Author",
-  Description = "Description",
-  Warmup = "Warmup",
-  Rest = "Rest",
-  Interval = "Interval",
-  Cooldown = "Cooldown",
-}
-
-type Rule = {
-  type: RuleType;
-  params: Param[];
-};
-
-enum ParamType {
-  Text = "Text",
-  Power = "Power",
-  PowerRange = "PowerRange",
-  Cadence = "Cadence",
-  Duration = "Duration",
-}
-
-type TextParam = { type: ParamType.Text; value: string };
-type PowerParam = { type: ParamType.Power; value: number };
-type PowerRangeParam = { type: ParamType.PowerRange; value: [number, number] };
-type CadenceParam = { type: ParamType.Cadence; value: number };
-type DurationParam = { type: ParamType.Duration; value: number };
-
-type Param =
-  | TextParam
-  | PowerParam
-  | PowerRangeParam
-  | CadenceParam
-  | DurationParam;
-
-const toInteger = (str: string): number => {
-  return parseInt(str.replace(/[^0-9]/, ""), 10);
-};
-
-const toSeconds = (str: string): number => {
-  const [seconds, minutes, hours] = str.split(":").map(toInteger).reverse();
-  return seconds + minutes * 60 + (hours || 0) * 60 * 60;
-};
-
-const parseValueParam = (text: string): Param => {
-  if (/^[0-9:]+$/.test(text)) {
-    return { type: ParamType.Duration, value: toSeconds(text) };
-  }
-  if (/^[0-9]+rpm$/.test(text)) {
-    return { type: ParamType.Cadence, value: toInteger(text) };
-  }
-  if (/^[0-9]+%..[0-9]+%$/.test(text)) {
-    const [from, to] = text.split("..").map(toInteger);
-    return { type: ParamType.PowerRange, value: [from, to] };
-  }
-  if (/^[0-9]+%$/.test(text)) {
-    return { type: ParamType.Power, value: toInteger(text) };
-  }
-  throw new Error(`Unrecognized parameter "${text}"`);
-};
-
-const parseParams = (type: RuleType, text: string): Param[] => {
-  switch (type) {
-    case RuleType.Name:
-    case RuleType.Author:
-    case RuleType.Description:
-      return [{ type: ParamType.Text, value: text }];
-    case RuleType.Warmup:
-    case RuleType.Rest:
-    case RuleType.Interval:
-    case RuleType.Cooldown:
-      return text.split(" ").map(parseValueParam);
-  }
-};
-
-const parseRule = (line: string): Rule | undefined => {
-  const matches = line.match(/^(\w+):(.*)$/);
-  if (!matches) {
-    return undefined;
-  }
-  if (!Object.keys(RuleType).includes(matches[1])) {
-    return undefined;
-  }
-  const type: RuleType = matches[1] as RuleType;
-
-  return {
-    type,
-    params: parseParams(type, matches[2].trim()),
-  };
-};
+import { parseRule } from "./parser";
 
 const isDefined = <T>(x: T | undefined): x is T => Boolean(x);
 
diff --git a/src/parser.ts b/src/parser.ts
new file mode 100644
index 0000000..a645e3f
--- /dev/null
+++ b/src/parser.ts
@@ -0,0 +1,57 @@
+import { Param, ParamType, RuleType, Rule } from "./ast";
+
+const toInteger = (str: string): number => {
+  return parseInt(str.replace(/[^0-9]/, ""), 10);
+};
+
+const toSeconds = (str: string): number => {
+  const [seconds, minutes, hours] = str.split(":").map(toInteger).reverse();
+  return seconds + minutes * 60 + (hours || 0) * 60 * 60;
+};
+
+const parseValueParam = (text: string): Param => {
+  if (/^[0-9:]+$/.test(text)) {
+    return { type: ParamType.Duration, value: toSeconds(text) };
+  }
+  if (/^[0-9]+rpm$/.test(text)) {
+    return { type: ParamType.Cadence, value: toInteger(text) };
+  }
+  if (/^[0-9]+%..[0-9]+%$/.test(text)) {
+    const [from, to] = text.split("..").map(toInteger);
+    return { type: ParamType.PowerRange, value: [from, to] };
+  }
+  if (/^[0-9]+%$/.test(text)) {
+    return { type: ParamType.Power, value: toInteger(text) };
+  }
+  throw new Error(`Unrecognized parameter "${text}"`);
+};
+
+const parseParams = (type: RuleType, text: string): Param[] => {
+  switch (type) {
+    case RuleType.Name:
+    case RuleType.Author:
+    case RuleType.Description:
+      return [{ type: ParamType.Text, value: text }];
+    case RuleType.Warmup:
+    case RuleType.Rest:
+    case RuleType.Interval:
+    case RuleType.Cooldown:
+      return text.split(" ").map(parseValueParam);
+  }
+};
+
+export const parseRule = (line: string): Rule | undefined => {
+  const matches = line.match(/^(\w+):(.*)$/);
+  if (!matches) {
+    return undefined;
+  }
+  if (!Object.keys(RuleType).includes(matches[1])) {
+    return undefined;
+  }
+  const type: RuleType = matches[1] as RuleType;
+
+  return {
+    type,
+    params: parseParams(type, matches[2].trim()),
+  };
+};