[squeak-dev] valid characters for binary selector

Jecel Assumpcao Jr. jecel at merlintec.com
Mon May 27 19:52:07 UTC 2019

Chris Muller wrote on Sat, 25 May 2019 18:08:28 -0500
> I was looking for every valid character allowed as part of a binary selector
> name.  Nothing in SelectorNode was obvious to me, but the AST diagram in
> my copy of Smalltalk-80, The Language and Implementation, says they are:
>      - + / * ~ < > = @ % | & ? !
> Is this still correct?

In code this is defined in method Scanner class>initialize where
everything is a binary character by default, then tab lf ff cr space are
redefined as delimiters, then the digits are redefined, then the letters
and then "  #  $  '  :  (  )  .  ;  [  ]  {  }  ^  _ | each get their
own token type. This means characters from 128 to 255 are also valid in
binary selectors and even a bunch of control characters!

> It also seems to indicate that - (minus) is only allowed all by itself, not with
> any of the others.
> The others are limited to a maximum of two.
> However, I was just able to save (compile) a method named - at +.   So is it
> okay / advisable to go beyond the original spec if it lets me?

This is defined in Scanner>>xBinary

The two character limit is no longer there and the only restriction
relative to $- is that it can't be immediately followed by a digit (in
which case we can't tell if it is supposed to be the sign of the
following number or the last character of the binary selector).

I would avoid creating selectors that would not be valid in other
Smalltalks if I might want to port my code later on. In the ANSI
Smalltalk standard binary selectors can have any number of characters,
but these must only be ! % & * + , / < = > ? @ \ ~ | -

Binary selectors with the vertical bar are valid in ANSI but not in
Squeak (they can mess things up with the block syntax and so aren't a
good idea anyway).

-- Jecel

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