1 files changed, 40 insertions, 0 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,
+  })
+