The examples in perlfunc demonstrate this syntax quite neatly:

Any function (...) may be used either with or without parentheses around its arguments. (...) If you use parentheses, the simple but occasionally surprising rule is this: It looks like a function, therefore it is a function, and precedence doesn't matter. Otherwise it's a list operator or unary operator, and precedence does matter. Whitespace between the function and left parenthesis doesn't count, so sometimes you need to be careful:

    print 1+2+4; # Prints 7.
    print(1+2) + 4; # Prints 3.
    print (1+2)+4; # Also prints 3!
    print +(1+2)+4; # Prints 7.
    print ((1+2)+4); # Prints 7.
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