Document some of the IR; not much to say, actually.

src/ir/ast.rs

@@ -1,3 +1,4 @@
+use crate::syntax::Location;
 use internment::ArcIntern;
 use pretty::{DocAllocator, Pretty};
 use proptest::{
@@ -5,13 +6,18 @@ use proptest::{
     strategy::{BoxedStrategy, Strategy},
 };
 
-use crate::syntax::Location;
-
+/// We're going to represent variables as interned strings.
+/// 
+/// These should be fast enough for comparison that it's OK, since it's going to end up
+/// being pretty much the pointer to the string.
 type Variable = ArcIntern<String>;
 
+/// The representation of a program within our IR. For now, this is exactly one file.
 #[derive(Debug)]
 pub struct Program {
-    pub statements: Vec<Statement>,
+    // For now, a program is just a vector of statements. In the future, we'll probably
+    // extend this to include a bunch of other information, but for now: just a list.
+    pub(crate) statements: Vec<Statement>,
 }
 
 impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Program
@@ -23,6 +29,8 @@ where
         let mut result = allocator.nil();
 
         for stmt in self.statements.iter() {
+            // there's probably a better way to do this, rather than constantly
+            // adding to the end, but this works.
             result = result
                 .append(stmt.pretty(allocator))
                 .append(allocator.text(";"))
@@ -44,6 +52,10 @@ impl Arbitrary for Program {
     }
 }
 
+/// The representation of a statement in the language.
+/// 
+/// For now, this is either a binding site (`x = 4`) or a print statement
+/// (`print x`). Someday, though, more!
 #[derive(Debug)]
 pub enum Statement {
     Binding(Location, Variable, Expression),
@@ -71,6 +83,7 @@ where
     }
 }
 
+/// The representation of an expression.
 #[derive(Debug)]
 pub enum Expression {
     Value(Location, Value),

src/ir/eval.rs

@@ -4,6 +4,10 @@ use crate::ir::{Expression, Program, Statement};
 use super::{Primitive, ValueOrRef};
 
 impl Program {
+    /// Evaluate the program, returning either an error or a string containing everything
+    /// the program printed out.
+    /// 
+    /// The print outs will be newline separated, with one print out per line.
     pub fn eval(&self) -> Result<String, EvalError> {
         let mut env = EvalEnvironment::empty();
         let mut stdout = String::new();
@@ -39,6 +43,9 @@ impl Expression {
             Expression::Primitive(_, op, args) => {
                 let mut arg_values = Vec::with_capacity(args.len());
 
+                // we implement primitive operations by first evaluating each of the
+                // arguments to the function, and then gathering up all the values
+                // produced.
                 for arg in args.iter() {
                     match arg {
                         ValueOrRef::Ref(_, n) => arg_values.push(env.lookup(n.clone())?),
@@ -48,6 +55,8 @@ impl Expression {
                     }
                 }
 
+                // and then finally we call `calculate` to run them. trust me, it's nice
+                // to not have to deal with all the nonsense hidden under `calculate`.
                 match op {
                     Primitive::Plus => Ok(Value::calculate("+", arg_values)?),
                     Primitive::Minus => Ok(Value::calculate("-", arg_values)?),

src/ir/strings.rs

@@ -3,6 +3,10 @@ use internment::ArcIntern;
 use std::collections::HashSet;
 
 impl Program {
+    /// Get the complete list of strings used within the program.
+    /// 
+    /// For the purposes of this function, strings are the variables used in
+    /// `print` statements.
     pub fn strings(&self) -> HashSet<ArcIntern<String>> {
         let mut result = HashSet::new();