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|
{ depot, ... }:
let
inherit (depot.nix)
yants
;
inherit (depot.users.sterni.nix)
fun
;
# we must avoid evaluating any of the sublists
# as they may contain conditions that throw
condition = yants.restrict "condition"
(ls: builtins.length ls == 2)
(yants.list yants.any);
/* Like the common lisp macro: takes a list
of two elemented lists whose first element
is a boolean. The second element of the
first list that has true as its first
element is returned.
Type: [ [ bool a ] ] -> a
Example:
cond [
[ (builtins.isString true) 12 ]
[ (3 == 2) 13 ]
[ true 42 ]
]
=> 42
*/
cond = conds: switch true conds;
/* Generic pattern match-ish construct for nix.
Takes a bunch of lists which are of length
two and checks the first element for either
a predicate or a value. The second value of
the first list which either has a value equal
to or a function that evaluates to true for
the given value.
Type: a -> [ [ (function | a) b ] ] -> b
Example:
switch "foo" [
[ "smol" "SMOL!!!" ]
[ (x: builtins.stringLength x <= 3) "smol-ish" ]
[ (fun.const true) "not smol" ]
]
=> "smol-ish"
*/
switch = x: conds:
if builtins.length conds == 0
then builtins.throw "exhausted all conditions"
else
let
c = condition (builtins.head conds);
s = builtins.head c;
b =
if builtins.isFunction s
then s x
else x == s;
in
if b
then builtins.elemAt c 1
else switch x (builtins.tail conds);
in {
inherit
cond
switch
;
}
|
