User:Zzo38/Proposal for macros
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This document list proposal for use of macros in Haskell.
Defining macros
Macros for catching pattern failure
Example:
a :: Int -> Int -> Int;
a 0 x = x;
a 1 x = x + x;
b :: Int -> Int -> Either String Int;
b = _Catch 2 a;
c :: Int -> Int -> IO Int;
c = _CatchIO 2 a;
d :: Int -> IO (Int -> Int);
d = _CatchIO 1 a;
e :: [String];
e = ["hello", "world", undefined];
f :: IO [String];
f = _CatchStrictIO 0 e do {
case _This of {
[] <- _Stop;
h : t <- do {
h;
_Again t;
};
};
};
Meanings:
b 0 = Right; b 2 = const $ Left "pattern match error"; c 0 = return; c 2 = const $ fail "pattern match error"; d 0 = return id; f = fail "undefined";