Things I like about Pascal [part 1]: == ≠ =

One of the things that pleases me no end about Pascal, like Algol before it, is its use of = to mean =, and not as an assignment operator. For that we have :=.

Dunno if it's my maths background, but I find languages that use the equals sign as an assignment operator to be really, really annoying.

Now good old BASIC gets it right, in that it uses = to test for equality but combines = with the LET prefix for assignment. As in:

LET x = 42

You know, just like you do in maths. Except that many BASIC implementations make LET optional!

But in the curly brace languages (and others), the misuse of = irritates me beyond reason. Especially so when they then go and define == to mean "is equal to" when there's a perfectly good = sign just begging to be used. I find this ridiculous - and I'm in good company:

A notorious example for a bad idea was the choice of the equal sign to denote assignment. It goes back to Fortran in 1957, and has blindly been copied by armies of language designers. Why is it a bad idea? Because it overthrows a century old tradition to let “=” denote a comparison for equality, a predicate which is either true or false. But Fortran made it to mean assignment, the enforcing of equality. In this case, the operands are on unequal footing: The left operand (a variable) is to be made equal to the right operand (an expression). x = y does not mean the same thing as y = x.

—Niklaus Wirth, Good Ideas, Through the Looking Glass

If a language doesn't want to use LET, it does makes sense to use different operators for assignment and equality, if only to help the compiler. But why get them the wrong way round and end up using two operators, neither of which make sense? Given that ← isn't available on most keyboards then Pascal's good old := operator seems to be a reasonable choice, although personally I'd have preferred <- (as in R).

And, AND

What's all this mess with ===? It doesn't even mean the same thing across the different languages that use it - see here for an explanation.

Why doesn't Pascal have such an operator? Strict typing perhaps?

Where did == originate?

It seems that the first use of = as an assignment operator may have been as far back as in Superplan [1951],  but where does == come from? I've traced it back to B [c1969], but was there an earlier language that used it? Please comment if you know.

Even though B was based on BCPL, the latter used the := assignment operator. This was changed to = in  B, so the equality operator was changed from = to == as a consequence. Marvellous!

What do you think?

I know there are some others who find this misuse of the = sign annoying, but what about you? Comments please!


Comments

Post a Comment

Comments are very welcome, but please don't comment here if:

1) You have a query about, or a bug report for, one of my programs or libraries. Most of my posts contain a link to the relevant repository where there will be an issue tracker you can use.

2) You have a query about any 3rd party programs I feature, please address them to the developer(s) - there will be a link in the post.

3) You're one of the tiny, tiny minority who are aggressive or abusive - in the bin you go and reported you will be!

Thanks

Popular posts from this blog

Initialising dynamic arrays

When writing some unit tests a while ago I found myself needing to initialise some dynamic arrays with test data. It would be nice if we could do something like this: var A : array of Integer ; begin A := ( 1 , 2 , 3 , 4 ) ; // !! WRONG end ; but we can't. So I decided to write some functions to initialise dynamic arrays to the contents of another array, be it a constant, a literal or another dynamic array. The result was a set of overloaded routines, one for each data type I needed to handle, for example for Integer and string arrays I had: function CloneArray ( const A : array of Integer ) : TIntegerDynArray ; overload ; var Idx : Integer ; begin SetLength ( Result , Length ( A ) ) ; for Idx := Low ( A ) to High ( A ) do Result [ Idx - Low ( A ) ] := A [ Idx ] ; end ; function CloneArray ( const A : array of string ) : TStringDynArray ; overload ; var Idx : Integer ; begin SetLength ( Result , Len...
Read more

Deleting elements from a dynamic array

In my blog " Initialising Dynamic Arrays " I mentioned I have been writing some unit tests that needed numerous repetative array initialisation operations. Well, one of the other common operations I found myself writing was the deletion of items from dynamic arrays. So I decided to find a generic way of doing this. Assuming we know the index of the item to be deleted we need the equivalent of Delphi's built-in Delete procedure for strings. If you read the previous post you won't be surprised to learn that I decided to further extend the Generics.Collections.TArray class by adding to the TArrayEx class I introduced there. My first attempt emulates Delphi's Delete procedure by deleting the array element in-place: i.e. it updates the array passed as a parameter. Unsurprisingly the method is called DeleteInPlace . Here's how it goes: type TArrayEx = class ( TArray ) public .. . class procedure DeleteInPlace < T > ( var A : ...
Read more

New String Property Editor Planned For RAD Studio 12 Yukon 🤞

Image
This blog post is based on a pre-release version of the RAD Studio software and it has been written with specific permission by Embarcadero. No feature is committed until the product GA release. It seems I'm getting very excited about multi-line strings of late. My previous post was about multi-line string literals for Delphi  and this time I'm talking about the new multi-line string property editor being slated for the RAD Studio 12 IDE. For more years than I care to remember, I've been frustrated by the inability to enter multi-line strings in the Delphi IDE object inspector. That meant having to resort to code to initialise some multi-line labels. So frustrated was I that I wrote a little property editor of my own ( stringpe ), way back in 2004. It's still around and on GitHub. Here's what it (sometimes) looks like: Yeah, I know this is Vista - I used an old screenshot Sometimes? Well it looked like that until it got installed on DPI aware Delphis, and then it sh...
Read more