Parsing very long literal sequences is broken in several ways

[fingolfin]

When reading input, literal sequences exceeding the size of the Value buffer (i.e. more than 1024 characters) are handled by ReadLongNumber in src/read.c. This is broken in several ways. Here are some examples. Warning very long input lines. Naturally.

# integer with 1100 digts: works
gap> 12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890;;

# overlong identifier starting with a letter: correctly detected
gap> x12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890;
Syntax error: Identifiers in GAP must consist of less than 1023 characters.
...

# overlong identifier starting with a digit: wrong error message (identifiers cannot exceed 1023 characters)
gap> gap> 1x2345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890;
Error, Variable: '1x2345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\
01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890\
12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901\
23456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012\
34567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123\
45678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234\
56789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345\
6789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901
not in any function at *stdin*:1

# overlong identifier, with first non-digit coming after the 1024 character mark: GAP gets completely confused, ends on continuation prompt
gap> 12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890x;
Syntax error: Identifier over 1024 characters
12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901\
23456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012\
34567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123\
45678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234\
56789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345\
67890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456\
78901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567\
89012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678\
9012345678901234567890123456789012345678901234567890x;
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                                                    ^
Error, Int: Invalid parsing (internal error)
not in any function at *stdin*:
>

[fingolfin]

... and you can find more if you e.g. insert periods, which triggers the float code, or records; and can also lead to GAP actually evaluating part of the expression:

# leading period: fine
gap> .12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890;
0.123457

# trailing period after more than 1024 digits: fine
gap> 12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890.;
inf

# leading and trailing period (with more than 1024 digits in between): nonsenes
gap> .12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890.;
Syntax error: Record component name expected
.1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890\
12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901\
23456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012\
34567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123\
45678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234\
56789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345\
67890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456\
78901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567\
89012345678901234567890123456789012345678901234567890.;
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                                                      ^

[ChrisJefferson]

The second error here occurs at much shorter lengths:

gap> .123.;
Syntax error: Record component name expected
.123.;

This is coming in the following way:

• Parse a float: .123, successfully.
• We can, given any GAP expression X, try parsing X.y as a record expression.

Technically, we can't even assume that .123.x isn't valid GAP, because a custom float package could turn .123 into a record-type structure!

That's not to say we should improve this error, or stop floats being records.

The same thing occurs parsing 1 . or 1. .

[stevelinton]

You don't need demented custom float packages. Someone could install a method for ELM_REC for IsFloat. You could even imagine wanting x.mantissa and x.exponent to return suitable things.