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