verdict from the bench: taking stock is free, updating is ruinous

The word upstream is that the unstable builtin benchmark tests are
likely to be deprecated (rust-lang/rust#29553), but I didn't feel like
learning Criterion just for this.

test
inference::triangle::tests::concerning_the_expense_of_computing_entropy
... bench:           0 ns/iter (+/- 0)
test inference::triangle::tests::concerning_the_expense_of_updating
... bench:   1,485,967 ns/iter (+/- 81,055)

I'm not sure how to interpret the zero for computing the entropy; I
assume some sort of clever LLVM optimization has sloughed off the work
to compile time.

But yeah, that 1.5 million nanoseconds to do an update is way too explosive
for a hotspot like `value_of_information`. We're going to need some new
techniques.

src/inference/triangle/mod.rs

@@ -156,7 +156,10 @@ pub fn complexity_prior(basic_hypotheses: Vec<BasicHypothesis>)
 
 #[cfg(test)]
 mod tests {
+    use test::Bencher;
+
     use super::*;
+    use play::triangle::our_basic_hypotheses;
     use triangles::{Color, Size, Stack, Study, Triangle};
     use inference::triangle::hypotheses::{BasicHypothesis, JoinedHypothesis};
     use inference::triangle::hypotheses::color_count_boundedness::ColorCountBoundednessHypothesis;
@@ -234,4 +237,20 @@ mod tests {
                                Color::Red, 1)))));
     }
 
+    #[bench]
+    fn concerning_the_expense_of_updating(bencher: &mut Bencher) {
+        let distribution = complexity_prior(our_basic_hypotheses());
+        bencher.iter(|| {
+            distribution.updated(&Study::sample(), true);
+        });
+    }
+
+    #[bench]
+    fn concerning_the_expense_of_computing_entropy(bencher: &mut Bencher) {
+        let distribution = complexity_prior(our_basic_hypotheses());
+        bencher.iter(|| {
+            distribution.entropy();
+        });
+    }
+
 }

src/main.rs

@@ -1,9 +1,10 @@
-#![feature(iter_arith)]
+#![feature(iter_arith, test)]
 
 extern crate argparse;
 extern crate ansi_term;
 extern crate itertools;
 extern crate rand;
+extern crate test;
 
 #[macro_use] mod display;
 #[macro_use] mod triangles;

src/play/mod.rs

@@ -1,5 +1,5 @@
 mod number;
-mod triangle;
+pub mod triangle;
 
 
 use argparse::{ArgumentParser, Store, StoreTrue};

src/play/triangle.rs

@@ -8,13 +8,7 @@ use inference::triangle::hypotheses::color_count_boundedness::ColorCountBoundedn
 use inference::triangle::hypotheses::size_count_boundedness::SizeCountBoundednessHypothesis;
 
 
-pub fn play() {
-    wrapln!("Welcome to Mezzanine v. {}! Privately think of a criterion. \
-             This program will attempt to efficiently infer the nature of \
-             the criterion by asking you whether specific studies do or do \
-             not have the property of satisfying the criterion.",
-             env!("CARGO_PKG_VERSION"));
-
+pub fn our_basic_hypotheses() -> Vec<BasicHypothesis> {
     let mut hypotheses = Vec::new();
     for &color in Color::iter() {
         for lower in 1..4 {
@@ -45,8 +39,19 @@ pub fn play() {
                         size, upper)));
         }
     }
+    hypotheses
+}
+
+
+pub fn play() {
+    wrapln!("Welcome to Mezzanine v. {}! Privately think of a criterion. \
+             This program will attempt to efficiently infer the nature of \
+             the criterion by asking you whether specific studies do or do \
+             not have the property of satisfying the criterion.",
+             env!("CARGO_PKG_VERSION"));
 
-    let mut beliefs = complexity_prior(hypotheses);
+    let basic_hypotheses = our_basic_hypotheses();
+    let mut beliefs = complexity_prior(basic_hypotheses);
     println!("Size of hypothesis space: {}", beliefs.len());
 
     loop {