pyrox.dev
doc: Render lib.fixedPoints
+1
doc/default.nix
+1
doc/default.nix
···
11
{ name = "strings"; description = "string manipulation functions"; }
12
{ name = "versions"; description = "version string functions"; }
13
{ name = "trivial"; description = "miscellaneous functions"; }
14
{ name = "lists"; description = "list manipulation functions"; }
15
{ name = "debug"; description = "debugging functions"; }
16
{ name = "options"; description = "NixOS / nixpkgs option handling"; }
···
11
{ name = "strings"; description = "string manipulation functions"; }
12
{ name = "versions"; description = "version string functions"; }
13
{ name = "trivial"; description = "miscellaneous functions"; }
14
+
{ name = "fixedPoints"; baseName = "fixed-points"; description = "explicit recursion functions"; }
15
{ name = "lists"; description = "list manipulation functions"; }
16
{ name = "debug"; description = "debugging functions"; }
17
{ name = "options"; description = "NixOS / nixpkgs option handling"; }
+10
-7
doc/doc-support/lib-function-docs.nix
+10
-7
doc/doc-support/lib-function-docs.nix
···
14
buildInputs = [ nixdoc ];
15
installPhase = ''
16
function docgen {
17
-
# TODO: wrap lib.$1 in <literal>, make nixdoc not escape it
18
-
if [[ -e "../lib/$1.nix" ]]; then
19
-
nixdoc -c "$1" -d "lib.$1: $2" -l ${locationsJSON} -f "$1.nix" > "$out/$1.md"
20
else
21
-
nixdoc -c "$1" -d "lib.$1: $2" -l ${locationsJSON} -f "$1/default.nix" > "$out/$1.md"
22
fi
23
-
echo "$out/$1.md" >> "$out/index.md"
24
}
25
26
mkdir -p "$out"
···
29
```{=include=} sections
30
EOF
31
32
-
${lib.concatMapStrings ({ name, description }: ''
33
-
docgen ${name} ${lib.escapeShellArg description}
34
'') libsets}
35
36
echo '```' >> "$out/index.md"
···
14
buildInputs = [ nixdoc ];
15
installPhase = ''
16
function docgen {
17
+
name=$1
18
+
baseName=$2
19
+
description=$3
20
+
# TODO: wrap lib.$name in <literal>, make nixdoc not escape it
21
+
if [[ -e "../lib/$baseName.nix" ]]; then
22
+
nixdoc -c "$name" -d "lib.$name: $description" -l ${locationsJSON} -f "$baseName.nix" > "$out/$name.md"
23
else
24
+
nixdoc -c "$name" -d "lib.$name: $description" -l ${locationsJSON} -f "$baseName/default.nix" > "$out/$name.md"
25
fi
26
+
echo "$out/$name.md" >> "$out/index.md"
27
}
28
29
mkdir -p "$out"
···
32
```{=include=} sections
33
EOF
34
35
+
${lib.concatMapStrings ({ name, baseName ? name, description }: ''
36
+
docgen ${name} ${baseName} ${lib.escapeShellArg description}
37
'') libsets}
38
39
echo '```' >> "$out/index.md"
+115
-81
lib/fixed-points.nix
+115
-81
lib/fixed-points.nix
···
1
{ lib, ... }:
2
rec {
3
-
# Compute the fixed point of the given function `f`, which is usually an
4
-
# attribute set that expects its final, non-recursive representation as an
5
-
# argument:
6
-
#
7
-
# f = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
8
-
#
9
-
# Nix evaluates this recursion until all references to `self` have been
10
-
# resolved. At that point, the final result is returned and `f x = x` holds:
11
-
#
12
-
# nix-repl> fix f
13
-
# { bar = "bar"; foo = "foo"; foobar = "foobar"; }
14
-
#
15
-
# Type: fix :: (a -> a) -> a
16
-
#
17
-
# See https://en.wikipedia.org/wiki/Fixed-point_combinator for further
18
-
# details.
19
fix = f: let x = f x; in x;
20
21
-
# A variant of `fix` that records the original recursive attribute set in the
22
-
# result. This is useful in combination with the `extends` function to
23
-
# implement deep overriding. See pkgs/development/haskell-modules/default.nix
24
-
# for a concrete example.
25
fix' = f: let x = f x // { __unfix__ = f; }; in x;
26
27
-
# Return the fixpoint that `f` converges to when called recursively, starting
28
-
# with the input `x`.
29
-
#
30
-
# nix-repl> converge (x: x / 2) 16
31
-
# 0
32
converge = f: x:
33
let
34
x' = f x;
···
37
then x
38
else converge f x';
39
40
-
# Modify the contents of an explicitly recursive attribute set in a way that
41
-
# honors `self`-references. This is accomplished with a function
42
-
#
43
-
# g = self: super: { foo = super.foo + " + "; }
44
-
#
45
-
# that has access to the unmodified input (`super`) as well as the final
46
-
# non-recursive representation of the attribute set (`self`). `extends`
47
-
# differs from the native `//` operator insofar as that it's applied *before*
48
-
# references to `self` are resolved:
49
-
#
50
-
# nix-repl> fix (extends g f)
51
-
# { bar = "bar"; foo = "foo + "; foobar = "foo + bar"; }
52
-
#
53
-
# The name of the function is inspired by object-oriented inheritance, i.e.
54
-
# think of it as an infix operator `g extends f` that mimics the syntax from
55
-
# Java. It may seem counter-intuitive to have the "base class" as the second
56
-
# argument, but it's nice this way if several uses of `extends` are cascaded.
57
-
#
58
-
# To get a better understanding how `extends` turns a function with a fix
59
-
# point (the package set we start with) into a new function with a different fix
60
-
# point (the desired packages set) lets just see, how `extends g f`
61
-
# unfolds with `g` and `f` defined above:
62
-
#
63
-
# extends g f = self: let super = f self; in super // g self super;
64
-
# = self: let super = { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }; in super // g self super
65
-
# = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // g self { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
66
-
# = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // { foo = "foo" + " + "; }
67
-
# = self: { foo = "foo + "; bar = "bar"; foobar = self.foo + self.bar; }
68
-
#
69
extends = f: rattrs: self: let super = rattrs self; in super // f self super;
70
71
-
# Compose two extending functions of the type expected by 'extends'
72
-
# into one where changes made in the first are available in the
73
-
# 'super' of the second
74
composeExtensions =
75
f: g: final: prev:
76
let fApplied = f final prev;
77
prev' = prev // fApplied;
78
in fApplied // g final prev';
79
80
-
# Compose several extending functions of the type expected by 'extends' into
81
-
# one where changes made in preceding functions are made available to
82
-
# subsequent ones.
83
-
#
84
-
# composeManyExtensions : [packageSet -> packageSet -> packageSet] -> packageSet -> packageSet -> packageSet
85
-
# ^final ^prev ^overrides ^final ^prev ^overrides
86
composeManyExtensions =
87
lib.foldr (x: y: composeExtensions x y) (final: prev: {});
88
89
-
# Create an overridable, recursive attribute set. For example:
90
-
#
91
-
# nix-repl> obj = makeExtensible (self: { })
92
-
#
93
-
# nix-repl> obj
94
-
# { __unfix__ = «lambda»; extend = «lambda»; }
95
-
#
96
-
# nix-repl> obj = obj.extend (self: super: { foo = "foo"; })
97
-
#
98
-
# nix-repl> obj
99
-
# { __unfix__ = «lambda»; extend = «lambda»; foo = "foo"; }
100
-
#
101
-
# nix-repl> obj = obj.extend (self: super: { foo = super.foo + " + "; bar = "bar"; foobar = self.foo + self.bar; })
102
-
#
103
-
# nix-repl> obj
104
-
# { __unfix__ = «lambda»; bar = "bar"; extend = «lambda»; foo = "foo + "; foobar = "foo + bar"; }
105
makeExtensible = makeExtensibleWithCustomName "extend";
106
107
-
# Same as `makeExtensible` but the name of the extending attribute is
108
-
# customized.
109
makeExtensibleWithCustomName = extenderName: rattrs:
110
fix' (self: (rattrs self) // {
111
${extenderName} = f: makeExtensibleWithCustomName extenderName (extends f rattrs);
···
1
{ lib, ... }:
2
rec {
3
+
/*
4
+
Compute the fixed point of the given function `f`, which is usually an
5
+
attribute set that expects its final, non-recursive representation as an
6
+
argument:
7
+
8
+
```
9
+
f = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
10
+
```
11
+
12
+
Nix evaluates this recursion until all references to `self` have been
13
+
resolved. At that point, the final result is returned and `f x = x` holds:
14
+
15
+
```
16
+
nix-repl> fix f
17
+
{ bar = "bar"; foo = "foo"; foobar = "foobar"; }
18
+
```
19
+
20
+
Type: fix :: (a -> a) -> a
21
+
22
+
See https://en.wikipedia.org/wiki/Fixed-point_combinator for further
23
+
details.
24
+
*/
25
fix = f: let x = f x; in x;
26
27
+
/*
28
+
A variant of `fix` that records the original recursive attribute set in the
29
+
result, in an attribute named `__unfix__`.
30
+
31
+
This is useful in combination with the `extends` function to
32
+
implement deep overriding.
33
+
*/
34
fix' = f: let x = f x // { __unfix__ = f; }; in x;
35
36
+
/*
37
+
Return the fixpoint that `f` converges to when called iteratively, starting
38
+
with the input `x`.
39
+
40
+
```
41
+
nix-repl> converge (x: x / 2) 16
42
+
0
43
+
```
44
+
45
+
Type: (a -> a) -> a -> a
46
+
*/
47
converge = f: x:
48
let
49
x' = f x;
···
52
then x
53
else converge f x';
54
55
+
/*
56
+
Modify the contents of an explicitly recursive attribute set in a way that
57
+
honors `self`-references. This is accomplished with a function
58
+
59
+
```nix
60
+
g = self: super: { foo = super.foo + " + "; }
61
+
```
62
+
63
+
that has access to the unmodified input (`super`) as well as the final
64
+
non-recursive representation of the attribute set (`self`). `extends`
65
+
differs from the native `//` operator insofar as that it's applied *before*
66
+
references to `self` are resolved:
67
+
68
+
```
69
+
nix-repl> fix (extends g f)
70
+
{ bar = "bar"; foo = "foo + "; foobar = "foo + bar"; }
71
+
```
72
+
73
+
The name of the function is inspired by object-oriented inheritance, i.e.
74
+
think of it as an infix operator `g extends f` that mimics the syntax from
75
+
Java. It may seem counter-intuitive to have the "base class" as the second
76
+
argument, but it's nice this way if several uses of `extends` are cascaded.
77
+
78
+
To get a better understanding how `extends` turns a function with a fix
79
+
point (the package set we start with) into a new function with a different fix
80
+
point (the desired packages set) lets just see, how `extends g f`
81
+
unfolds with `g` and `f` defined above:
82
+
83
+
```
84
+
extends g f = self: let super = f self; in super // g self super;
85
+
= self: let super = { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }; in super // g self super
86
+
= self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // g self { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
87
+
= self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // { foo = "foo" + " + "; }
88
+
= self: { foo = "foo + "; bar = "bar"; foobar = self.foo + self.bar; }
89
+
```
90
+
*/
91
extends = f: rattrs: self: let super = rattrs self; in super // f self super;
92
93
+
/*
94
+
Compose two extending functions of the type expected by 'extends'
95
+
into one where changes made in the first are available in the
96
+
'super' of the second
97
+
*/
98
composeExtensions =
99
f: g: final: prev:
100
let fApplied = f final prev;
101
prev' = prev // fApplied;
102
in fApplied // g final prev';
103
104
+
/*
105
+
Compose several extending functions of the type expected by 'extends' into
106
+
one where changes made in preceding functions are made available to
107
+
subsequent ones.
108
+
109
+
```
110
+
composeManyExtensions : [packageSet -> packageSet -> packageSet] -> packageSet -> packageSet -> packageSet
111
+
^final ^prev ^overrides ^final ^prev ^overrides
112
+
```
113
+
*/
114
composeManyExtensions =
115
lib.foldr (x: y: composeExtensions x y) (final: prev: {});
116
117
+
/*
118
+
Create an overridable, recursive attribute set. For example:
119
+
120
+
```
121
+
nix-repl> obj = makeExtensible (self: { })
122
+
123
+
nix-repl> obj
124
+
{ __unfix__ = «lambda»; extend = «lambda»; }
125
+
126
+
nix-repl> obj = obj.extend (self: super: { foo = "foo"; })
127
+
128
+
nix-repl> obj
129
+
{ __unfix__ = «lambda»; extend = «lambda»; foo = "foo"; }
130
+
131
+
nix-repl> obj = obj.extend (self: super: { foo = super.foo + " + "; bar = "bar"; foobar = self.foo + self.bar; })
132
+
133
+
nix-repl> obj
134
+
{ __unfix__ = «lambda»; bar = "bar"; extend = «lambda»; foo = "foo + "; foobar = "foo + bar"; }
135
+
```
136
+
*/
137
makeExtensible = makeExtensibleWithCustomName "extend";
138
139
+
/*
140
+
Same as `makeExtensible` but the name of the extending attribute is
141
+
customized.
142
+
*/
143
makeExtensibleWithCustomName = extenderName: rattrs:
144
fix' (self: (rattrs self) // {
145
${extenderName} = f: makeExtensibleWithCustomName extenderName (extends f rattrs);