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evaluate.js
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evaluate.js
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'use strict';
import Result from './result.js';
import AST from './ast.js';
const evaluate = (expression) => {
if (expression.type == 'application' &&
expression.elements.length > 0 &&
expression.elements[0].type == 'identifier') {
const head = expression.elements[0];
if (head.value == '+') {
if (expression.elements.length < 2) {
return Result.failure('+ requires at least 1 argument');
}
let total = 0;
for (const element of expression.elements.slice(1)) {
const i = evaluate(element);
if (!Result.isSuccess(i)) {
return i;
}
if (i.value.type != 'number') {
return Result.failure('+ can only operate on numbers');
}
total += i.value.value;
}
return Result.success(AST.numberExpression(total));
}
if (head.value == '-') {
if (expression.elements.length < 2) {
return Result.failure('- requires at least 1 argument');
}
let total = 0;
for (const element of expression.elements.slice(1)) {
const i = evaluate(element);
if (!Result.isSuccess(i)) {
return i;
}
if (i.value.type != 'number') {
return Result.failure('- can only operate on numbers');
}
total -= i.value.value;
}
return Result.success(AST.numberExpression(total));
}
if (head.value == '*') {
if (expression.elements.length < 2) {
return Result.failure('* requires at least 1 argument');
}
let total = 1;
for (const element of expression.elements.slice(1)) {
const i = evaluate(element);
if (!Result.isSuccess(i)) {
return i;
}
if (i.value.type != 'number') {
return Result.failure('* can only operate on numbers');
}
total *= i.value.value;
}
return Result.success(AST.numberExpression(total));
}
if (head.value == '/') {
if (expression.elements.length < 3) {
return Result.failure('/ requires at least 2 arguments');
}
const i = evaluate(expression.elements[1]);
if (!Result.isSuccess(i)) {
return i;
}
if (i.value.type != 'number') {
return Result.failure('/ can only operate on numbers');
}
let total = i.value.value;
for (const element of expression.elements.slice(2)) {
const i = evaluate(element);
if (!Result.isSuccess(i)) {
return i;
}
if (i.value.type != 'number') {
return Result.failure('/ can only operate on numbers');
}
total /= i.value.value;
}
return Result.success(AST.numberExpression(total));
}
return Result.failure('Unrecognized operator ' + head.value);
}
return Result.success(expression);
};
module.exports = {
evaluate
};