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(g77-295.info)Context-Sensitive Intrinsicness

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Context-Sensitive Intrinsicness
-------------------------------

   `g77' treats procedure references to *possible* intrinsic names as
always enabling their intrinsic nature, regardless of whether the
*form* of the reference is valid for that intrinsic.

   For example, `CALL SQRT' is interpreted by `g77' as an invalid
reference to the `SQRT' intrinsic function, because the reference is a
subroutine invocation.

   First, `g77' recognizes the statement `CALL SQRT' as a reference to
a *procedure* named `SQRT', not to a *variable* with that name (as it
would for a statement such as `V = SQRT').

   Next, `g77' establishes that, in the program unit being compiled,
`SQRT' is an intrinsic--not a subroutine that happens to have the same
name as an intrinsic (as would be the case if, for example, `EXTERNAL
SQRT' was present).

   Finally, `g77' recognizes that the *form* of the reference is
invalid for that particular intrinsic.  That is, it recognizes that it
is invalid for an intrinsic *function*, such as `SQRT', to be invoked as
a *subroutine*.

   At that point, `g77' issues a diagnostic.

   Some users claim that it is "obvious" that `CALL SQRT' references an
external subroutine of their own, not an intrinsic function.

   However, `g77' knows about intrinsic subroutines, not just
functions, and is able to support both having the same names, for
example.

   As a result of this, `g77' rejects calls to intrinsics that are not
subroutines, and function invocations of intrinsics that are not
functions, just as it (and most compilers) rejects invocations of
intrinsics with the wrong number (or types) of arguments.

   So, use the `EXTERNAL SQRT' statement in a program unit that calls a
user-written subroutine named `SQRT'.