←back to thread

Parse, don't validate (2019)

(lexi-lambda.github.io)
398 points declanhaigh | 1 comments | 07 Mar 23 08:47 UTC | HN request time: 0s | source
Show context
bruce343434 ◴[07 Mar 23 10:54 UTC] No.35053912[source]▶
Note that this basically requires your language to have ergonomic support for sum types, immutable "data classes", pattern matching.

The point is to parse the input into a structure which always upholds the predicates you care about so you don't end up continuously defensively programming in ifs and asserts.

replies(12): >>35054046 #>>35054070 #>>35054386 #>>35054514 #>>35054901 #>>35054993 #>>35055124 #>>35055230 #>>35056047 #>>35057866 #>>35058185 #>>35059271 #
Thaxll ◴[07 Mar 23 13:08 UTC] No.35054901[source]▶
You're describing deserialization in a strong typing language, sometimes it's not enough, ok your email went to an empty string which is useless.
replies(2): >>35054943 #>>35055012 #
Kinrany ◴[07 Mar 23 13:14 UTC] No.35054943[source]▶
You can have a ValidEmail type that performs all the checks on construction.
replies(1): >>35055657 #
Thaxll ◴[07 Mar 23 14:25 UTC] No.35055657[source]▶
OP said to not validate.
replies(3): >>35055815 #>>35056190 #>>35060605 #
1. mrkeen ◴[07 Mar 23 15:13 UTC] No.35056190[source]▶
That's fine.

Validation would be:

   Email email = new Email(anyString);
   email.validate();
Parsing (in OP's context) would be:

   Either<Error, ValidEmail> eEmail = Email.from(anyString);