Multiple left single quotes

Posted on 2008-10-11 20:12 By jakubi ( Maple Rating 4

925)

Categories:

For a single pair of left single quotes, ?name is clear:

Any valid Maple name formed without using left single quotes is precisely the same as the name formed by surrounding the name with left single quotes.

So this is fine:

`x`;
                      x

But what about multiple left single quotes? This help page also states:

A name may also be formed by enclosing any sequence of characters in a pair of left single quotes

Any sequence of characters includes a sequence of left single quotes, but another story of parsers occurs.

1D input:

``x``;

Error, missing operator or `;`

```x```;

                      `x`

````x````;

Error, missing operator or `;`

`````x`````;

                      ``x``

Not clear which is the issue here (something about the empty name?).

2D standard input:

``x``;

                        ``^2*x

```x```;

                        ``^2*x

````x````;

                        ``^4*x

`````x`````;

                        ``^4*x

Nice effect (when typeset). A product is implied and the empty name commutes with 'x'. And yet...

2D clasic input:

``x``;

Unable to convert "``x``;" to an expression

```x```;

                        `\`x\``

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Comments

I think this is as expected

Comment on 2008-11-03 08:40 from tobybailey (

85)

It's just the usual issue - in 1D input they need escaping for the obvious reason of ambiguity:

`\`x\``;

really does produce `x` as a name.

In 2_D input I have no idea what's going on and don't much care - I can't see any use for 2D input myself.

Toby

2D standard

Comment on 2008-11-24 11:42 from JacquesC ( Maple Rating 4

1699)

[Yep, I am a full 3 weeks behind reading Primes, and I am unlikely to catch-up today, just wandering around on a couple of interesting posts]

The explanation here is also simple: invisible times. `` is the empty name `x` is the name x; so ```x``` is then taken to be the same as `` `x` `` which is indeed ``^2*x.

Part of the issue is that ` is 1-sided, unlike (), [] and {}, so you cannot easily figure out which ` belongs with which other `. Uniformly choosing the closest-one, while otherwise respecting the language grammar, produces the effects you report here. There is no clear-cut way of doing this, so this becomes part of the "grammar design".