Correct syntax of let ... in and where clauses in Haskell -


i trying declare local variables (is right term in case of haskell?) in haskell using , let-in clauses. whenever clauses longer single line parse errors:

> letexample :: int -> int > letexample 0 = 0 > letexample n = >               let 1     = 1 >                   4    = 4 >                   8   = 8 >               in one*four*eight

when trying load above code ghci following error:

letexample.lhs:4:33: parse error in let binding: missing required 'in' failed, modules loaded: none.

i following error when trying load code below:

whereexample:5:57: parse error on input ‘=’ failed, modules loaded: none.

code:

> whereexample :: int -> int > whereexample 0 = 0 > whereexample n = 1 * 4 * 8 >                 1     = 1 >                       4    = 4 >                       8   = 8

what right way of using let , in above cases?

the posted code mixes tabs , spaces. frequent cause of indentation problems.

the haskell report, defined language, states tabs equivalent 8 spaces. if editor configured display tabs number of spaces, chances reading indented @ correct level not compiler.

the easiest fix replace tab spaces in source files. that, recommend turning on warnings passing -wall flag, or adding

{-# options -wall #-}

at beginning of source files. doing cause ghc warn when tabs detected.

there alternative solutions drastic remove-all-tabs one. there smart ways mix tabs , spaces in "tab-agnostic" way, make code compilable , readable in spite of how many spaces tab equivalent to. while is not popular, such proposals have technical merits.


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