Due to the way the counter is constructed in the HKDF specification,
the requested output length can be at most 255 times the size of the
digest algorithm's output.
Reported by @notoria in #527. Many thanks!
This is useful to generate keys and initialization vectors
from suitable input keying material, so that future predicates
for symmetric encryption can be used with appropriate parameters.
This is useful to establish shared secrets, using ECDH key exchange.
Note that CLP(ℤ) goal expansion is currently disabled due to #445,
and this slows down the computations considerably for the time being.
For instance, consider:
t(X) :- X #= 1.
We *cannot* expand this to:
?- listing(t/1).
t(A) :-
( integer(A) ->
A=:=A
; ( var(A) ->
true
; true,
clpz:clpz_equal(A,A)
)
).
Also, a new binding *must not* be dragged outside of disjunctions,
since the code may look for example like this:
i(X) :-
( X #= 3
; X #= 4
).
This commit fixes such issues, and still rewrites CLP(ℤ) expressions
as far as possible already at compilation time.
For example:
n(X) :- X #= 1+3.
This is now compiled to (note that 1+3 is evaluated to 4):
?- listing(n/1).
n(A) :-
( integer(A) ->
A=:=4
; ( var(A) ->
A=4
; B=4,
clpz:clpz_equal(A,B)
)
).
Ideally, it should be compiled to:
n(4).
This is especially important because a few of our names diverge from
ctype(3), and we better inform programmers when the type they are
using is not available at all.
Example:
:- dynamic(a/1).
a(X) :- X = true, b(X).
Yielding:
?- listing(a/1).
%@ a(A) :-
%@ A=true,
%@ b(A).
%@ true.
listing/1 only works for predicates and DCGs that are declared dynamic/1.
This works best when used in tandem with ~N+, since it is currently
equivalent to ~0| and does not take the actual text position into account.
However, when using relative positions, this works as intended.
This is to accommodate goals that are used for their side-effects,
when we are interested in their output.
Examples:
?- portray_clause((a :- a)).
a :-
a.
true
; false.
?- format("hello~w~n", [!]).
hello!
true
; false.
The preceding use of atom_length/2 already ensures that C has the
correct type (i.e., atom). However, its domain may still be wrong,
if its length is greater than 1.
The preceding use of atom_length/2 already ensures that C has the
correct type (i.e., atom). However, its domain may still be wrong,
if its length is greater than 1.
Pairs must be keysorted and may also contain variables as keys.
Examples:
?- group_pairs_by_key([1-a,1-b,2-c], Ps).
Ps = [1-[a,b],2-[c]].
?- group_pairs_by_key([X-a,X-b,2-c], Ps).
Ps = [X-[a,b],2-[c]].
At the moment, library(format) seems to be a fitting place.
In the eventual library organization, portray_clause/1 and
related predicates may be moved to their own dedicated library.
library(clpz) implements declarative integer arithmetic.
The most important predicates for reasoning about integers are:
(#=)/2 equality
(#\=)/2 disequality
(#<)/2 less than
(#>)/2 greater than
(#=<)/2 less than or equal to
(#>=)/2 greater than or equal to
In addition, the library provides several global constraints, such as
all_distinct/1 and global_cardinality/2, and reification predicates
that reflect the truth values of constraints into integer variables.
Enumeration predicates such label/1 and labeling/2 can be used to
search for solutions over finite domains.
Almost all Prolog programs also reason about integers. Therefore, I
recommend to add this library to your .scryerrc configuration file so
that declarative integer arithmetic is available in all your programs.
More information about CLP(ℤ):
https://www.metalevel.at/prolog/clpz
Enjoy!
This library provides the nonterminal format_//2 to describe
formatted strings. format/2 is provided for impure output.
Usage:
======
phrase(format_(FormatString, Arguments), Ls)
format_//2 describes a list of characters Ls that are formatted
according to FormatString. FormatString is a string (i.e.,
a list of characters) that specifies the layout of Ls.
The characters in FormatString are used literally, except
for the following tokens with special meaning:
~w use the next available argument from Arguments here,
which must be atomic (a current limitation)
~f use the next argument here, a floating point number
~Nf where N is an integer: format the float argument
using N digits after the decimal point
~s use the next argument here, which must be a string
~N| where N is an integer: place a tab stop at text column N
~N+ where N is an integer: place a tab stop N characters
after the previous tab stop (or start of line)
~t distribute spaces evenly between the two closest tabstops
~`Ct like ~t, use character C instead of spaces to fill the space
~n newline
~~ the literal ~
The predicate format/2 is like format_//2, except that it outputs
the text on the terminal instead of describing it declaratively.
If at all possible, format_//2 should be used, to stress pure parts
that enable easy testing etc. If necessary, you can emit the list Ls
with maplist(write, Ls).
The entire library only works if the Prolog flag double_quotes
is set to chars, the default value in Scryer Prolog. This should
also stay that way, to encourage a sensible environment.
Example:
?- phrase(format_("~s~n~`.t~w!~12|", ["hello",there]), Cs).
%@ Cs = [h,e,l,l,o,'\n','.','.','.','.','.','.',t,h,e,r,e,!] ;
%@ false.
Markus Triska