f786d21b0f
@aqjune @nunoplopes: This commit adds basic support for random numbers. It defines a random number generator interface, and an basic implementation based on the Haskell one. We can add more implementations in the future if neeeded. The new test program has a few examples. BTW, this is a pure Lean implementation. If we need more performance we can provide an implementation using C++.
58 lines
1.8 KiB
Text
58 lines
1.8 KiB
Text
import system.random
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universes u
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def tst1 : nat :=
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let s := mk_std_gen, /- create standard random number generator -/
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(v, s') := rand_nat s 0 100 /- generate a random nat in [0, 100]. -/
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in v
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#eval tst1
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def tst2 : bool × bool × bool × bool :=
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let s := mk_std_gen, /- create standard random number generator -/
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(b₁, s₁) := rand_bool s, /- generate a random Boolean -/
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(b₂, s₂) := rand_bool s₁, /- generate another random Boolean -/
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(b₃, s₃) := rand_bool s₂,
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(b₄, _) := rand_bool s₃
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in (b₁, b₂, b₃, b₄)
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#eval tst2
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/- `rand_list sz g lo hi` generates a list of size `sz` with
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random nat's in [lo, hi] generated by `g`. -/
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def rand_list : nat → std_gen → nat → nat → list nat × std_gen
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| 0 g lo hi := ([], g)
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| (n+1) g lo hi :=
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let (l, g₁) := rand_list n g lo hi,
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(v, g₂) := rand_nat g₁ lo hi
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in (v::l, g₂)
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#eval (rand_list 20 mk_std_gen 0 10).1
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/- Version of rand_list that is parametrized by any random number generator implementation -/
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def gen_rand_list {gen : Type u} [random_gen gen] : nat → gen → nat → nat → list nat × gen
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| 0 g lo hi := ([], g)
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| (n+1) g lo hi :=
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let (l, g₁) := gen_rand_list n g lo hi,
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(v, g₂) := rand_nat g₁ lo hi
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in (v::l, g₂)
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#eval (gen_rand_list 20 mk_std_gen 0 10).1
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/- We can implement our own number generators.
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Here is a 'dumb' one that just generates a sequence -/
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structure dummy_gen :=
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(lo hi : nat)
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(next : nat := lo)
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instance : random_gen dummy_gen :=
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{ range := λ s, (s.lo, s.hi),
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next := λ s, (s.next, {next := s.next + 1, ..s}),
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split := λ s, (s, s) }
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def mk_dummy_gen (lo : nat := 0) (hi : nat := 100000) : dummy_gen :=
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{lo := lo, hi := hi}
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/- Invoke gen_rand_list using the dummy generator. -/
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#eval (gen_rand_list 20 mk_dummy_gen 0 10).1
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