Numeric Literals (Summary 5)

[Michael Lazzaro]

With clarifications, and additional syntactic edge cases.

The last remaining known "numeric literals" issue is whether we want to allow '.' in explicit radix, e.g. 10#1.234, or whether we want to disallow it as being Way Too Creepy. This version assumes that '.' is allowed, but exponential notation is _not_, due to ambiguities with 'E'.


--- Numeric Literals ---

decimal notation:
123 # int 123
0123 # int 123 (not octal!)
123.0 # num 123.0
-123 # int -123 (but - is operator, not part of num)

0_1.2_3 # ok
_01.23 # WRONG
01.23_ # WRONG
01_._23 # WRONG
1__2 # WRONG

0.1 # ok
0.1.1 # WRONG, can have only one decimal point
.1 # WRONG; looks like method call on $_
-.1 # WRONG, looks like method call on $_

exponential notation:
-1.23e4 # num
-1.23E4 # num (identical)
1.23_e_4 # WRONG (underscore only between digits)

1e4 # ok
0e4 # ok, == 0
0e0 # ok, == 0
1e0 # ok, == 1
e4 # WRONG, looks like func
.e4 # WRONG, looks like method

bin/oct/hex notation:

0d6789 # decimal
0b0110 # bin
0o0123 # oct
0x00ff # hex
0x00fF # hex, == 0x00ff
0x00FF # hex, == 0x00ff

-0xff # ok
-0x00ff # ok
0x-ff # WRONG, - is an operator, not part of the literal

0xf_f # ok
0x_ff # WRONG, underscore only between digits

0x0 # ok, == 0
0x0.0 # ok
0x.0 # ok
0d1.1E5 # WRONG, exp not allowed in shorthand radix

0B0110 # WRONG, should be 0b0110
0O0123 # WRONG, should be 0o0123
0X00FF # WRONG, should be 0x00FF

explicit radix:

(radix 2-36)

20#1gj # base 20
20#1GJ # base 20 (identical)
20#1:G:J # base 20 (identical)
20#1_G_J # base 20 (identical)
20#1:16:19 # base 20 (identical)
20#1_16_19 # NOT identical, == 20:11619
20#1:1_6:19 # WRONG: colon form may not have underlines

20#0:0:1 # base 20
20#0:1 # base 20 (identical)
20#:1 # base 20 (identical) (leading : is ok)
:1 # WRONG, need radix specifier
20# # WRONG, need at least an '0'
1#0 # WRONG, radix must be >= 2

20#1_G.J # ok, radix point (e.g. float) allowed
20#1:16.19 # ok, radix point (e.g. float) allowed
10#1.1E5 # WRONG, no exp notation in explicit radix

-20#1GJ # base 20 (negative)
-20#1:16:19 # base 20 (negative)
20#-1GJ # WRONG, - is an operator, not part of the literal

(radix 37-RADIX_MAX)

256#0:253:254:255 # base 256
256#:253:254:255 # base 256 (identical)
256#0_253_254_255 # WRONG, digit 253254255 doesn't
# exist in base 256.


Other issues w/ literals:

- radix <= 36, alpha digits may be upper or lowercase
- radix > 36, only colon form is allowed, not alpha digits
- underlines may appear ONLY between digits
- colon form may therefore not have underlines
- radix < 2 throws error
- negative sign goes before radix, e.g. -20#1GJ.
- need to specify RADIX_MAX (platform dependent?)
- explicit radix form may have radix point, '.',
but cannot use exponential notation ('e')

- can't have runtime radix, e.g. 2**8#10, because # binds tighter.
- can't say (2**8)#10, because not a literal.

MikeL