Make scanner accept floating point literals in hex and binary #9106
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When the call to erl_scan succeeded returning more than one token, for example "123_", the unexpected success was not detected.
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In cases such as "123a45", the scanner did not report an error, instead returning two tokens '123' and 'a45'. The splitting point depends on the base, so e.g., "16#12fg34" was scanned as '16#12f' and 'g34'. This change makes the scanner reject numbers immediately followed by a name character.
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Rebased on #9104 after squashing. |
bjorng
reviewed
Nov 27, 2024
| "1.e2", | ||
| "12._34", | ||
| "123.a4" | ||
| ], | ||
| lists:foreach( | ||
| fun(S) -> | ||
| case erl_scan:string(S) of |
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To improve code coverage, I suggest updating the existing helper function erl_scan_string/3 like this:
erl_scan_string(String, StartLocation, Options) ->
case erl_scan:string(String, StartLocation, Options) of
{ok, Tokens, EndLocation} ->
{ok, unopaque_tokens(Tokens), EndLocation};
{error,{_,Mod,Reason},_}=Error ->
Mod:format_error(Reason),
Error
end.
Then replace all calls to erl_scan:string/1 in this PR with erl_scan_string/1.
Suggested change
| case erl_scan:string(S) of | |
| case erl_scan_string(S) of |
bjorng
reviewed
Nov 27, 2024
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Similar to hex float literals in C 99, but using Erlang's Base#Literal notation we can easily have binary as well. For example, 2#0.10101p8, or 16#fefe.fefep-16. The letter p (as in C99) stands for powers of 2. The exponent, like the base, is always a decimal number.
These can be useful for code generators and other cases where you want to preserve an exact bit representation of a float.
Also allows explicit base 10 for completeness, as in 10#123.345e9 (with the letter e for exponent as normal - p not allowed, since it would make it very easy to miss whether it is a power of 2 or 10).
Currently missing: documentation. Might also need an EEP.
Based on #9104, which improves pinpointing of errors in numerical literals.