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Another noobie question about logical operations
f#book

Hey guys, i just got myself Chris Smith's book and went into explorations of F#land))

You know, before i've read about indentations instead of curly braces, i spent like 20 minutes typing and retyping the code for the first program and trying to figure out what's going on.

Oh, my background is C++ and PHP.

Anyway, my question is this:

somewhere in the code he's got something like this

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let pt f =
   printfn " some text | %5b |" (f true true)
   ();;

And it could be called like this pt(&&) or pt(||). He used it as a demo for booleans.

Now, i got everything except for the part in braces. I mean, i understand that it takes my func's argument and uses it to compare true with true. But what confuses me is the way it's written.

And related to this - why can't i have is returning true if i write && true true? It's the same thing, isn't it?

.

In F#, infix operators (which include the logical operators, but also addition, subtraction, etc.) can be treated like normal functions if they are parenthesized. So 1 + 2 is the same as (+) 1 2, and therefore if you want to pass an operator to a function which expects a function argument, you must also wrap it in parentheses.

By on 6/1/2010 9:36 AM ()

Oh, thanks.

So in this example the call should be like pt (&&) not pt(&&) if i understood correctly because it's not like im calling pt() with &&, instead, i call pt with (&&).

Is there a way in F# to explicitly require x(arg) call instead of x arg? or accept both?

By on 6/1/2010 9:49 AM ()

In this case I don't think the space makes a difference.
In general, if you have a function of 1 arguments, using () or not is the same:

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let f a = a*a
f 2
f(3)

This two functions, on the contrary are different:

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let f  a  b  = a+b
let g (a, b) = a*b


f 2 3
g(2,3)

The first one takes 2 arguments, the second only one, typed as a tuple of two values.
The first notation allows partial application, the second doesn't.

HTH :)

By on 6/1/2010 11:02 AM ()

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