Re: Need help with basic functional programming
On Tuesday, 22 July 2014 at 17:09:29 UTC, bearophile wrote:
Eric:
while (!buf.empty())
{
p++;
buf.popFront();
Those () can be omitted, if you mind the noise (but you can
also keep them).
Actually, the ones behind `empty` and `front` are wrong, because
these are defined to be properties. They just happen to work
currently.
Re: Need help with basic functional programming
On Tuesday, 22 July 2014 at 17:09:29 UTC, bearophile wrote:
Eric:
while (!buf.empty())
{
p++;
buf.popFront();
Those () can be omitted, if you mind the noise (but you can
also keep them).
if (buf.front() <= '0' || buf.front() >= '9') break;
std.ascii.isDigit helps.
curTok.image = cast(string) cbuffer[0 .. (p -
cbuffer.ptr)].dup;
If you want a string, then idup is better. Try to minimize the
number of casts in your code.
auto s = buf.until("a <= '0' || a >= '9'");
Perhaps you need a ! after the until, or a !q{a <= '0' || a >=
'9'}.
Also, what is the fastest way to convert a range to a string?
The "text" function is the simplest.
Bye,
bearophile
Thanks! All very good suggestions...
-Eric
Re: Need help with basic functional programming
By the way, do you really mean to stop on '0' and '9'? Do you perhaps mean "a < '0' || a > '9'"? Yes, my bad...
Re: Need help with basic functional programming
On Tuesday, 22 July 2014 at 16:50:47 UTC, Eric wrote:
private void getNumber(MCInputStreamRange buf)
{
auto s = buf.until("a <= '0' || a >= '9'");
curTok.kind = Token_t.NUMBER;
curTok.image = to!string(s);
}
The problem is that "until" seems to not stop at the end of the
number,
and instead continues until the end of the buffer. Am I doing
something
wrong here?
You've forgotten the exclamation mark: buf.until!(...)
Without it, the string is not the predicate, but the sentinel
value. I.e. the range stops when it sees the characters "a <= '0'
|| a >= '9'".
By the way, do you really mean to stop on '0' and '9'? Do you
perhaps mean "a < '0' || a > '9'"?
Also, what is the fastest way to convert a range to a string?
The fastest to type is probably text(r) (or r.text). The fastest
for me to come up with is r.to!string, which does exactly the
same. I don't know about run time, but text/to!string is
hopefully fine.
Re: Need help with basic functional programming
Eric:
while (!buf.empty())
{
p++;
buf.popFront();
Those () can be omitted, if you mind the noise (but you can also
keep them).
if (buf.front() <= '0' || buf.front() >= '9') break;
std.ascii.isDigit helps.
curTok.image = cast(string) cbuffer[0 .. (p -
cbuffer.ptr)].dup;
If you want a string, then idup is better. Try to minimize the
number of casts in your code.
auto s = buf.until("a <= '0' || a >= '9'");
Perhaps you need a ! after the until, or a !q{a <= '0' || a >=
'9'}.
Also, what is the fastest way to convert a range to a string?
The "text" function is the simplest.
Bye,
bearophile
Need help with basic functional programming
I have been writing several lexers and parsers. The grammars I
need to
parse are really complex, and consequently I didn't feel
confident about
the code quality, especially in the lexers. So I decided to jump
on the functional progamming bandwagon to see if that would help.
It definitely
does help, there are fewer lines of code, and I feel better about
the code
quality. I started at the high level, and had the input buffer
return a
range of characters, and the lexer return a range of tokens. But
when I got
down to the lower levels of building up tokens, I ran into a
problem:
First I started with this which worked:
private void getNumber(MCInputStreamRange buf)
{
while (!buf.empty())
{
p++;
buf.popFront();
if (buf.front() <= '0' || buf.front() >= '9') break;
*p = buf.front();
}
curTok.kind = Token_t.NUMBER;
curTok.image = cast(string) cbuffer[0 .. (p -
cbuffer.ptr)].dup;
}
I thought I could improve this like so:
private void getNumber(MCInputStreamRange buf)
{
auto s = buf.until("a <= '0' || a >= '9'");
curTok.kind = Token_t.NUMBER;
curTok.image = to!string(s);
}
The problem is that "until" seems to not stop at the end of the
number,
and instead continues until the end of the buffer. Am I doing
something
wrong here? Also, what is the fastest way to convert a range to
a string?
Thanks,
Eric
