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  • Glasgow Haskell Compiler
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  • #7168

Closed
Open
Created Aug 20, 2012 by sjcjoosten@sjc

Loop

When patternmatching on (a,b), the variables a and b are sometimes evaluated eagerly, though they should not be. To see where this occurs, please try to evaluate f :

f = (1,error "this will not be evaluated!") .++. carefully f
(a,b) .++. (c,d) = (a+c,0)
carefully (a,b) = (1, a + b)

Note that the expected result here is (2,0). My workaround: the program works correctly if the last line is replaced by:

carefully x = (1, fst x + snd x)
Trac metadata
Trac field Value
Version 7.4.1
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
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