I want to handle string starts with number using pegjs. When I input with 1abcd it throws Expected [0-9.] or end of input but "a" found.. The expected output is { item: '1abcd', case: '=' }. What changes do I need?
var parser = peg.generate(`
start
= number:NUMBER { return { case: "=", item: number } }
/ string:STRING { return { case: "=", item: string.join("") } }
NUMBER
= number:[0-9\.]+ { return parseFloat(number.join("")); }
/ number:[0-9]+ { return parseInt(number.join(""), 10); }
STRING = string:[^*]+ { return string; }
`);
console.log(parser.parse("123"))
console.log(parser.parse("123.45"))
console.log(parser.parse("abcd"))
console.log(parser.parse("abcd-efgh"))
console.log(parser.parse("1abcd"))
The output as follows:
{case: "=", item: 123}
{case: "=", item: 123.45}
{case: "=", item: "abcd"}
{case: "=", item: "abcd-efgh"}
Sandbox: https://codesandbox.io/s/javascript-testing-sandbox-forked-5vekz?file=/src/index.js
Since NUMBER matches the first character, you'll want to use a negative lookahead for STRING before returning a successful match. That way, if a STRING character is encountered, the NUMBER rule will fail and the second alternation of start will be used.
Here's an example, although as @thinkgruen has written, you'll probably want to try to parse floats less loosely as well.
start
= number:NUMBER { return { case: "=", item: number } }
/ string:STRING { return { case: "=", item: string.join("") } }
NUMBER
= number:[0-9\.]+ (!STRING) { return parseFloat(number.join("")); }
/ number:[0-9]+ (!STRING) { return parseInt(number.join(""), 10); }
STRING = string:[^*]+ { return string; }