Heck no. We can do this ourselves. Remember, the textual transformation to transform let's is just that: a textual translation. It should be possible to create an automated translation tool (based off raymyers' treeparse) that will handle this for us.
Let the old version of 'let be Arc2Let, and the proposed new let be Arc2.7Let. Let the old version of 'with and 'withs be Arc2With and Arc2Withs, respectively. We need to determine if each Arc2Let in the source is composed of a single expression in the body. If it is, we leave it as-is. If it isn't, we simply replace it with Arc2.7As.
For each Arc2With we determine if the body is composed of a single expression. If it is, we replace it with Arc2.7Let, removing the parens around the Arc2With bindings. If it isn't, we leave it as-is. Ditto for Arc2Withs, replacing it with Arc2.7Lets.
We define an expression simply as a sequence of whitespace, base-expression, and whitespace. We define whitespace as being either a comment (either #||# or ;) or ordinary whitespace.
A base-expression is simply a symbol, a number, a character, a string, a quote-expression, a comma and comma-at expression, or a list. A quote-expression is simply the ' quote or ` backquote character followed by maybe whitespace, followed by an expression; comma and comma-at are defined similarly. A list is composed of an opening parenthesis followed by many expressions, followed by a closing parens.
We can determine if a 'let form has several expressions by defining two variants of a 'let form. An Arc2Let is composed of ( <maybe whitespace> let <whitespace> <expression> <expression> <expression> [many <expression>]), and that we have to transform to Arc2.7As (by filtering out the let expression using treeparse 'filt). An Arc2.7LetCompatible is composed of just (let <expression> <expression> <expression>), which we do not transform.
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Of course, this does represent a veritable fork of the Arc code ^^.
I would leave with and withs alone, so that we have the option of the implicit do (also because it makes it easier to implement given/Anarki-let :P). And why not use a code-tree-walker if we want to do this—isn't that the point of Lisp?
Right, comments. Just a little important, aren't they? :P
You raise a good point... it's the same number of parentheses either way. But in that case, why not just have let and lets (as given(s)), and be done with it?
Edit: as an aside, given that pg has said that he'll modify Arc as if there's nobody else programming in it, and that he does not appear to be using Anarki, eventually when Arc3 does come around, it is very possible that Anarki will be incompatible with Arc3. We may very well need to build a converter program in the future to transform Arc2-base Anarki to Arc3-base Anarki, so my abstract nonsense may very well be necessary in the future.
