treehouse/static/js/components/haku/treewalk.js

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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);