I can't seem to be able to reply to other replies (too much nesting probably). Perhaps I'll try the chatterbox or a separate question.

I was trying to understand if the Perl compiler parses "f ($_)" in "map f ($_), @numbers" as a lambda. If it's not a block, but an expression, it must be either an arithmetic expression, a lambda expression etc. My question was from a syntactic/compiler point of view.

And as to eager evaluation, obviously this is a counterexample, since map f($_) @nums doesn't immediately, eagerly evaluate f on the current $_, but instead passed a lambda to map()

Your use of syntax leaves me with the impression that before Perl you only knew Haskell, or some other, lazy / currying functional language.

The major difference between Perl and these others is that Perl is eager, so any unadorned mention of a function will simply call it. Unless you use built-in functions or fancy syntax tricks, all function parameters are passed in parentheses.

Creating/returning new functions is quite possible in Perl, but the usual approach is more eager in the sense of passing around values instead of passing around functions that, at some time in the future will be called to produce the final output of the program.

> Where can I read about functions that have comma and non-comma parsings?

in my own words:

BLOCK means { code } in curlies, like map { $_ +1 } 1..3, so no comma

  DB<124> map { $_ +1 } 1..3
 => (2, 3, 4)
[download]

EXPR can be any "atomar" code-snippet.

  DB<128> map  sqrt , 1..3
 => (1, "1.4142135623731", "1.73205080756888")

  DB<129> map  5 , 1..3
 => (5, 5, 5)
[download]

in both cases the list values are passed by setting a special variable (aka default variable) $_

according to perlglossary

       BLOCK
           A syntactic construct consisting of a sequence of Perl stat
+ements
           that is delimited by braces.  The "if" and "while" statemen
+ts are
           defined in terms of BLOCKs, for instance.  Sometimes we als
+o say
           "block" to mean a lexical scope; that is, a sequence of sta
+tements
           that act like a "BLOCK", such as within an eval or a file, 
+even
           though the statements aren’t delimited by braces.

...

       expression
           Anything you can legally say in a spot where a "value" is
           required.  Typically composed of literals, variables, opera
+tors,
           functions, and "subroutine" calls, not necessarily in that 
+order.
[download]

Cheers Rolf

( addicted to the Perl Programming Language)

f($_) means that you are calling the function, f, and passing it a scalar value contained in the $_ variable. See also perldoc perlsub