haku: a very shitty tree-walk interpreter

static/js/components/haku/treewalk.js

@@ -0,0 +1,42 @@
+export const treewalk = {};
+export const builtins = {};
+
+treewalk.init = (input) => {
+    return { input };
+};
+
+treewalk.eval = (state, node) => {
+    switch (node.kind) {
+        case "integer":
+            let sourceString = state.input.substring(node.start, node.end);
+            return parseInt(sourceString);
+
+        case "list":
+            let functionToCall = node.children[0];
+            let builtin = builtins[state.input.substring(functionToCall.start, functionToCall.end)];
+            return builtin(state, node);
+
+        default:
+            throw new Error(`unhandled node kind: ${node.kind}`);
+    }
+};
+
+export function run(input, node) {
+    let state = treewalk.init(input);
+    return treewalk.eval(state, node);
+}
+
+function arithmeticBuiltin(op) {
+    return (state, node) => {
+        let result = treewalk.eval(state, node.children[1]);
+        for (let i = 2; i < node.children.length; ++i) {
+            result = op(result, treewalk.eval(state, node.children[i]));
+        }
+        return result;
+    };
+}
+
+builtins["+"] = arithmeticBuiltin((a, b) => a + b);
+builtins["-"] = arithmeticBuiltin((a, b) => a - b);
+builtins["*"] = arithmeticBuiltin((a, b) => a * b);
+builtins["/"] = arithmeticBuiltin((a, b) => a / b);