[Haskell-cafe] List all multiply/add combinations

[Artyom Kazak]

Instead of attacking the problem textually, try to create a datatype which  
would describe your expressions, then generate all values of this  
datatype, filter those you don’t need, and convert the rest into Strings.  
Currently your expressions are represented by “String” — conversion is  
very cheap, but filtering is “hard” (since it boils down to parsing).  
Binary trees would suit you better.