Make it possible to evaluate monadic actions when assigning record fields (<-)
It is currently not possible to build records from values resulting from monadic actions while still using the field-specifiers.
foo :: IO Int
- ..
data Bar = Bar {
barFoo :: Int
}
buildBar :: IO () buildBar = do
return Bar {
barFoo <- foo --Evaluate foo to get the Int-value }
I've found two possible ways of doing this:
- Using temporaries to evaluate the actions before assigning which doubles the number of lines: tmp <- foo return Bar {
barFoo = tmp
}
- Lifting the record constructor which prevents you from using field specifiers (and you really need field specifiers when dealing with larger records): liftM Bar foo
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.6.1 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | Unknown |
| Architecture | Unknown |