add peek functionality? #80
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Added also a not() version of peek that operates the same, but returns the inverse err/ok values. |
Hejsil
reviewed
Feb 9, 2025
| pub fn peek(comptime parser: anytype) Parser(void) { | ||
| return _peek(parser, false); | ||
| } | ||
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A doc comment for peek and not please :)
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| test "peek" { | ||
| const fa = testing.failing_allocator; | ||
| const p1 = comptime ascii.range('a', 'z').peek(); | ||
| try expectOk(void, 0, {}, try p1.parse(fa, "a")); | ||
| try expectOk(void, 0, {}, try p1.parse(fa, "aa")); | ||
| try expectErr(void, 0, try p1.parse(fa, "1")); | ||
| } |
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I'd like to see a test case for not as well in case some refactor occurs and not no longer uses the same logic as peek
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Greetings - and thank you for this awesome module! Amazing demonstration of the power of Zig comptime!
I built a "peek" parser that does not consume anything, but checks to see if the nested parser parsed. It returns .ok if the nested parser parses with an index = 0. If the nested parser fails it returns .err with index = 0.
This was useful for parsing an identifier where I needed the first character to be alphabetic and the following characters could be alphanumeric. When I initially built this pattern, using a combine, the resulting type was a {u8, []u8} and required additional handling (e.g. didn't play well with other branches of a oneOf as the other branch returned []u8. Using peek inside the combine I was able to insist on the first character being alpha and yet still easily generate a []u8 return type.
Seems like this could be useful in other circumstances...?