#13013: Add readMaybe to Prelude (possibly readEither too), make Haddocks for read more cautionary -------------------------------------+------------------------------------- Reporter: sjakobi | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by sjakobi: @@ -32,1 +32,1 @@ - Ragarding point 2 (`readEither`), I have some qualms whether `readEither` + Regarding point 2 (`readEither`), I have some qualms whether `readEither` New description: = Motivation = `read` is an easy way to introduce runtime exceptions into programs, but its documentation doesn't sufficiently warn of this danger. `read`'s safe alternatives, `Text.Read.readMaybe` and `Text.Read.readEither`, are relatively unknown and too hard to find. = Proposal = == Summary == 1. Add `readMaybe` to the `Prelude` 2. Add `readEither` to the `Prelude` 3. Change the documentation for `read` to point out the partiality and to recommend the above alternatives. == 3. Improve the documentation for `read` == The haddocks for `read` currently read:
The `read` function reads input from a string, which must be completely consumed by the input process.
I propose to add the following paragraph:
Note: `read` will throw an error if the parse fails. If there's any uncertainty w.r.t. the shape of the input, `readMaybe` or `readEither` should be used instead.
== Qualifications == Regarding point 2 (`readEither`), I have some qualms whether `readEither` ([http://hackage.haskell.org/package/base-4.9.0.0/docs/Text- Read.html#v:readEither docs]) offers sufficient additional benefit over `readMaybe` to also warrant inclusion in `Prelude`. While `readEither` does give additional info on the kind of parse failures, that information is encoded in a `String` error message, from which it must be parsed if it is needed in the program. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13013#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler