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const tokenize = (pattern) => {
const tokens = [];
let i = 0;
while (i < pattern.length) {
const char = pattern[i];
if (char === '.' || char === '*' || char === '(' || char === ')' || char === '|') {
tokens.push({
type: char,
value: char
});
} else if (char === '\\') { // Handle escaped characters
i++;
tokens.push({
type: 'literal',
value: pattern[i]
});
} else if (char === '[') { // Handle character classes
let charClass = '';
i++;
while (pattern[i] !== ']' && i < pattern.length) {
charClass += pattern[i];
i++;
}
tokens.push({
type: 'charClass',
value: charClass
});
} else {
tokens.push({
type: 'literal',
value: char
});
}
i++;
}
return tokens;
};
const parse = (tokens) => {
let i = 0;
const parseSequenceExpression = () => {
const node = {
type: 'sequence',
elements: []
};
while (i < tokens.length) {
const token = tokens[i];
if (token.type === 'literal') {
node.elements.push({
type: 'literal',
value: token.value
});
} else if (token.type === '*') {
const lastElement = node.elements.pop();
node.elements.push({
type: 'star',
element: lastElement
});
} else if (token.type === '.') {
node.elements.push({
type: 'dot'
});
} else if (token.type === 'charClass') {
node.elements.push({
type: 'charClass',
value: token.value
});
} else if (token.type === '|') {
i++;
const right = parseSequenceExpression();
return {
type: 'alternation',
left: node,
right
};
} else if (token.type === '(') {
i++;
node.elements.push(parseSequenceExpression());
} else if (token.type === ')') {
break; // End of a grouping
}
i++;
}
return node;
};
return parseSequenceExpression();
};
const evaluateMatch = (node) => (input) => {
if (node.type === 'literal') {
return input[0] === node.value ? input.slice(1) : null;
}
if (node.type === 'dot') {
return input.length > 0 ? input.slice(1) : null;
}
if (node.type === 'star') {
let remainder = input;
while (remainder !== null) {
const next = evaluateMatch(node.element)(remainder);
if (next === null) {
break;
}
remainder = next;
}
return remainder;
}
if (node.type === 'charClass') {
return node.value.includes(input[0]) ? input.slice(1) : null;
}
if (node.type === 'alternation') {
const remainderLeft = evaluateMatch(node.left)(input);
const remainderRight = evaluateMatch(node.right)(input);
return remainderLeft !== null ? remainderLeft : remainderRight;
}
if (node.type === 'sequence') {
let remainder = input;
for (const element of node.elements) {
remainder = evaluateMatch(element)(remainder);
if (remainder === null) {
return null;
}
}
return remainder;
}
};
const assertEqual = (expected, actual, message) => {
if (expected !== actual) {
console.error(`FAIL: ${message}`);
} else {
console.log(`PASS: ${message}`);
}
};
const runTests = () => {
const tests = [{
pattern: "a.b*c",
input: "abbbc",
expected: true
},
{
pattern: "a.b*c",
input: "abc",
expected: true
},
{
pattern: "a.b*c",
input: "ac",
expected: true
},
{
pattern: "a.b*c",
input: "abbc",
expected: true
},
{
pattern: "a.b*c",
input: "axbc",
expected: false
},
// Character class tests
{
pattern: "[abc]x",
input: "bx",
expected: true
},
{
pattern: "[abc]x",
input: "dx",
expected: false
},
// Grouping and alternation tests
{
pattern: "(a|b)c",
input: "ac",
expected: true
},
{
pattern: "(a|b)c",
input: "bc",
expected: true
},
{
pattern: "(a|b)c",
input: "cc",
expected: false
},
// Escaped characters tests
{
pattern: "a\\.b",
input: "a.b",
expected: true
},
{
pattern: "a\\.b",
input: "a-b",
expected: false
},
{
pattern: "a\\*b",
input: "a*b",
expected: true
}
];
tests.forEach(({ pattern, input, expected }, index) => {
const tokens = tokenize(pattern);
const ast = parse(tokens);
const result = evaluateMatch(ast)(input) !== null;
assertEqual(expected, result, `Test ${index + 1}`);
});
};
runTests();
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