Assigning a value to a function does not produce a compilation error

[erik]

Take a look at this code:

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Function Foo(ByVal param As Integer)As Integer
	Return 2
End Function

Foo(3) = 5

I assign a value to the function. Why does not the compiler throw an error?

[jj2007]

You are right, it should throw an error. Gcc simply ignores the statement (and does not generate any code), while GAS calls the function with an argument zero (which doesn't make any sense):

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asm int 3
Foo(&H1234) = &H12345678
asm nop

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004015D5  |.  CC            int3                                     ; |
004015D6  |.  6A 00         push 0                                   ; |/Arg1 = 0
004015D8  |.  E8 B3FFFFFF   call 00401590                            ; |\TmpFb.00401590
004015DD  |.  90            nop                                      ; |

[SARG]

Same problem with a sub.

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Function Foo(ByVal param As Integer)As Integer
   Return 2
End Function

sub sFoo(ByVal param As Integer)
End sub

Foo(3) = 5
sfoo(3)= 5

sleep

[fxm]

This behavior only occurs for procedures with one and only one parameter.
This makes me think of functions returning by reference with one and only one parameter that must absolutely be surrounded by parentheses for the assignment.
Ultimately, the parser does not like this type of one-parameter syntax, on the left side of assignment expression.

[deltarho[1859]]

Of course what we should be getting is

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error 3: Expected End-of-Line, found '=' 

which we would get with two or more parameters.

I wouldn't have thought it too difficult to correct the parser.

[coderJeff]

Careful, '=' can be assignment or comparison for equality.
x = foo( (3) = 5 )

Also, return values from functions can be discarded:
foo( (3) = 5 )

And, parentheses are optional for procedures used as statements
foo (3) = 5

So in the example given in the OP, it's not an assignment. "(3)=5" is an expression passed to the first argument of foo() and the result discarded.

[erik]

To prevent such cases, I dream of a restriction in the language so that functions can only be called with parentheses and returned values from functions can not be discarded.

[fxm]

You dream of going back and even more!
See below an extract from 'changelog.txt':

Version 1.00.0 (former 0.91.0):

.....
[added]
.....
- Any function result may now be ignored at the call site (simply by not using the function result in any expression or assignment). Previously this was only allowed for functions returning integer types or pointers.
.....