[Haskell-cafe] pattern matching vs if-then-else

Maarten Faddegon haskell-cafe at maartenfaddegon.nl
Sun Aug 12 13:30:54 CEST 2012

Hi there,

I am writing a toy compiler in Haskell to further my skills in 
functional programming. One of the functions I wrote is to determine the 
iteration count of a loop. I have a number of different test that I want 
to do and I find myself now testing some of these using pattern matching 
and some properties using an if-then-else construction. I do not 
consider this very pretty.

My question is: are there guidelines of when to use pattern matching and 
when to use if-then-else?

Snippet of the function I mentioned:


itercount (ForLoop
                 [ ( Assignment update_lcv
                         (Op2 "+" (Content update_lcv') update_expr)
                 [(Assignment init_lcv init_expr)]
                 (TestStmt (Op2 "<" (Content test_lcv) test_expr))
         = if    -- All stmts use the same lcv
                    test_lcv == init_lcv
&& test_lcv == update_lcv
&& test_lcv == update_lcv'
                 -- And the lcv is not updated in the body
&& intersect [test_lcv] (blockkills bodyblock) == []
                 then Just $ simple_itercount init_expr test_expr 
                 else Nothing
itercount _ = Nothing


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