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Execute HQ9+: Difference between revisions
Console output is made using monads
(Added an Agena sample) |
(Console output is made using monads) |
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Line 720:
| be '+' = eval' xs (a+1)
| else = fail "Invalid instruction."
where be c = char.upper x == c
h = "Hello, world!"
q = src
Line 731:
++ bottles xs</lang>
It slightly alters an original HQ9+ specification. HQ9+ is an impure language that does console output. However console output is the only interaction that a user can see when executing HQ9+ program. This interpreter doesn't output to console but instead generates a list with all outputs. An accumulator is moved to the interpter arguments and the need for a reference cell is eliminated. Once an interpreter completes a client code can output to console using monads like so:
<lang ela>open
print_and_eval src = do
res <- return $ eval src
return $ each print res
where print x = do putStrLn x
print_and_eval "HQ9+" ::: IO</lang>
=={{header|Erlang}}==
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