Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
983 views
in Technique[技术] by (71.8m points)

haskell - Accessing a Specific Element in a Tuple

Haskell-newbie reporting in. Question is as follows: In Haskell, we have fst and snd that return the first and the second elements of a 2-tuple. Why don't we have an easy way of accessing the i-th element from any tuple? Right now I have a 3-tuple, I want to read the 1st element and the only way of accomplishing this task is doing pattern-matching trickery. Why can't this be done easier? Or maybe there is some easy way?

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

What prevents the language from having the special construct you want is its design. The designers just didn't put this in, because it would complicate the language definition, which is quite minimalistic. fst and snd are library functions for the common case of pairs; you can define all the others yourself, or better, define record types for your data so that your data members have appropriate names.

(It may be that GHC has an extension to do this, but I haven't encountered one; check the docs or ask on the mailing list to be sure.)


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...