5 files changed, 61 insertions, 13 deletions
diff --git a/src/eval.ts b/src/eval.ts
new file mode 100644
index 0000000..1e18457
--- /dev/null
+++ b/src/eval.ts
@@ -0,0 +1,40 @@
+import { Expr } from "./parser";
+import { match, matchString } from "./utils/adt";
+
+export type Dependencies = {
+  addClass(id: string, classes: string): Promise<void>
+  removeClass(id: string, classes: string): Promise<void>
+  // requestGetCss(url: string): Promise<string>
+  // getVarable(name: string, def?: string): Promise<string>
+  // updateVariable(id: string, varName: string, value: string): Promise<void>
+  // calculate ??
+}
+
+export const evalExpr = async (expr: Expr, deps: Dependencies): Promise<string | undefined> =>
+  match<Promise<string | undefined>, Expr>(expr, {
+    Call: async ({ name, args }) => {
+      await matchString(name, {
+        'add-class': async () => {
+          const id = await evalExpr(args[0], deps)
+          const classes = await evalExpr(args[1], deps)
+          if (id && classes) {
+            await deps.addClass(id, classes)
+          }
+        },
+        'remove-class': async () => {
+          const id = await evalExpr(args[0], deps)
+          const classes = await evalExpr(args[1], deps)
+          if (id && classes) {
+            await deps.removeClass(id, classes)
+          }
+        },
+        _: () => Promise.reject(new Error('not supposed to be here')),
+      })
+      return undefined
+    },
+    LiteralString: async s => s,
+    Identifier: async s => s,
+    VarIdentifier: async s => s,
+    _: async _ => undefined,
+  })
+
diff --git a/src/parse-expr.ts b/src/parser.ts
index 1c5c08f..1c5c08f 100644
--- a/src/parse-expr.ts
+++ b/src/parser.ts
diff --git a/src/utils/adt.ts b/src/utils/adt.ts
index e9a6c51..7234f67 100644
--- a/src/utils/adt.ts
+++ b/src/utils/adt.ts
@@ -5,6 +5,11 @@ export const match =
     [key in T['tag'] | '_']?: (v: TagValue<T, key>) => R
   }): R => ((pattern as any)[tag.tag] || (pattern._ as any))(tag.value)
 
+export const matchString =
+  <R, T extends string>(key: T, pattern: {
+    [key in T | '_']?: (key: key) => R
+  }): R => ((pattern as any)[key] || (pattern._ as any))(key)
+
 type Tag<N, V> = { tag: N; value: V }
 export type Enum<T> = { [N in keyof T]: Tag<N, T[N]> }[keyof T]
 
diff --git a/src/utils/parser-comb.ts b/src/utils/parser-comb.ts
index 49f633e..e0665f6 100644
--- a/src/utils/parser-comb.ts
+++ b/src/utils/parser-comb.ts
@@ -1,16 +1,5 @@
-import { Enum, constructors, match } from './adt';
-
-export type Result<V, E> = Enum<{ Ok: V, Err: E }>
-export const Result = constructors<Result<any, any>>()
-
-export const mapResult = <A, B, E>(res: Result<A, E>, fn: (_: A) => B): Result<B, E> =>
-  chainResult(res, a => Result.Ok(fn(a)))
-
-export const chainResult = <A, B, E>(res: Result<A, E>, fn: (_: A) => Result<B, E>): Result<B, E> =>
-  match(res, {
-    Ok: a => fn(a),
-    Err: e => Result.Err(e),
-  });
+import { match } from './adt';
+import { Result, mapResult, chainResult } from './result';
 
 export type ParseResult<T> = Result<{ value: T, input: string }, { error: string, input: string }>;
 
diff --git a/src/utils/result.ts b/src/utils/result.ts
new file mode 100644
index 0000000..c0120b8
--- /dev/null
+++ b/src/utils/result.ts
@@ -0,0 +1,14 @@
+import { Enum, constructors, match } from "./adt";
+
+export type Result<V, E> = Enum<{ Ok: V, Err: E }>
+export const Result = constructors<Result<any, any>>()
+
+export const mapResult = <A, B, E>(res: Result<A, E>, fn: (_: A) => B): Result<B, E> =>
+  chainResult(res, a => Result.Ok(fn(a)))
+
+export const chainResult = <A, B, E>(res: Result<A, E>, fn: (_: A) => Result<B, E>): Result<B, E> =>
+  match(res, {
+    Ok: a => fn(a),
+    Err: e => Result.Err(e),
+  });
+