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- Subject: Re: [PROPOSAL 5.4] alternate way of format/pack/unpack (in the string library)
- From: Tom N Harris <telliamed@...>
- Date: Sat, 27 May 2017 01:48:23 -0400
I wouldn't say minilanguages are "liked". Just that C++ iostream is even
less liked. And some of the concerns seemed frivolous to me. Why is it a
problem that format strings can't validate argument types ahead of time
when Lua is a dynamic language?
On 5/26/2017 5:14 PM, François Perrad wrote:
An implementation based on a minilanguage doesn't allow user extension,
for example, you cannot add a "%Q" option to `string.format` in pure Lua.
It isn't because format strings are a minilanguange that makes it
unextendable. The current implementation delegates interpretation of
format strings to the C runtime. A hypothetical Lua library could parse
the format strings itself while being extensible.
That said, an attempt to make the formatting language more Lua-like I
think should take cues from LPEG. Use simple composable objects to
define the format. A back-of-the-hand example is:
xy_format = "x = " .. dec() .. " y = " .. dec()
pi_format = "pi = " .. fixed(nil, 4)
dec2 = pad(dec(), 2, "0")
dec4 = pad(dec(), 4, "0")
date_format = dec2()/"day".."/"..dec2()/"month".."/"..dec4()/"year"