Comments on: Equivalent of and-let*?

By: ByersAurelia31

ByersAurelia31 — Wed, 10 Mar 2010 04:59:03 +0000

One acknowledges that our life is very expensive, but some people need money for different issues and not every person gets enough cash. So to receive quick home loans or consolidation loans should be a right way out.

By: Alexey Romanov

Alexey Romanov — Thu, 04 Dec 2008 17:55:47 +0000

Indent all lines the same amount, except the first one.

By: Alexey Romanov

Alexey Romanov — Thu, 04 Dec 2008 17:54:34 +0000

Hello, Maybe monad!
A Haskell version looks like this:

get-session request = do
cookies <- requestCookies request
p <- lookup “session_id” cookies
sidStr <- snd p
sid <- (readMaybe sidStr :: Maybe Integer) — readMaybe is not in the standard library for some reason, but is easy to write
guard (exact? sid) — not really, no exact/inexact distiction
sp <- lookup sid sessions
return (snd sp)

By: ventonegro

ventonegro — Wed, 03 Dec 2008 11:11:08 +0000

@Bogdan:

It’s nice to see Lua here! But you would have to intersperse the lines with “if not x then return false end”…

@Peter:

The assignment inside the “and” is a nice trick, I am really surprised. Nevertheless, the scope of the variables is the whole function, and there are a lot of “ands”!

By: Snell-Pym » I’m missing Scheme

Snell-Pym » I’m missing Scheme — Wed, 03 Dec 2008 01:29:57 +0000

[...] I came across Ventonegro’s post on and-let* and it set me thinking. The Lisp family of languages (which includes Scheme) are renowned for their [...]

By: Bogdan

Bogdan — Wed, 03 Dec 2008 00:27:06 +0000

I would say any language with logical shortcut evaluation can get away with something like

function get_session(req)
local cookies = request_cookies(req)
local p = cookies and cookies.session_id
local sid_str = p and p[1]
local sid_nr = sid_str and tonumber(sid_str)
…

But I agree the Scheme version (or even the Ruby one) is more to the point.

By: Tim Baga

Tim Baga — Tue, 02 Dec 2008 22:25:47 +0000

There are no ‘common’ way for such task. Maybe a bit stupid idea, but you can use something like ParseTree (http://parsetree.rubyforge.org/ParseTree/) to implement this macro in a way you would like it. Implementation won’t take more than 5-6 lines.

By: Peter Bex

Peter Bex — Tue, 02 Dec 2008 20:44:45 +0000

Forgot to enclose in PRE tags. Just indent according to taste

By: Peter Bex

Peter Bex — Tue, 02 Dec 2008 20:42:42 +0000

It’s actually deceptively simple:

def get_session(req)
cookies = request_cookies(req)
and p = cookies[:session_id]
and sid_str = p[1]
and sid_nr = sid_str.to_i
and sid.is_a?(Integer)
and sp = sessions[sid]
and sp[1]
end

By: Grant Rettke

Grant Rettke — Tue, 02 Dec 2008 19:55:08 +0000

You mean non-ugly Ruby, right?