error: `return` in block function

[lilyball]

Current rust incoming doesn't allow me to use return inside a lambda.

std::u8::range(0, 1, |_| return true )

produces (output taken from the IRC rusti bot):

<anon>:10:34: 10:45 error: `return` in block function
<anon>:10          std::u8::range(0, 1, |_| return true )
                                            ^~~~~~~~~~~
note: in expansion of fmt!
<anon>:9:12: 11:7 note: expansion site
error: aborting due to previous error
application terminated with error code 101

[catamorphism]

This is by design and we agreed it's not going to be changed. Sorry! (In this case, you can write |_| { true } equivalently. Early-return out of a lambda isn't supported.)

[graydon]

Further details: this has to do with preserving Tennent's correspondence principle (or at least prohibiting expressions for which we can't preserve it). See http://gafter.blogspot.ca/2006/08/tennents-correspondence-principle-and.html for some further rationale.

[lilyball]

@graydon Thanks for the link. I had not heard of Tennent's correspondence principle before.