move builtins from crate root to private module in compile

This module was introduced in #145 as a public module. But actually it is
only ever used by the compiler, and it doesn't really make sense outside
the compile because of its use of `ProgNode`.

We may want to later make the builtins module be an extension trait of
Constructible or something, but as long as it depends on ProgNode it
should not be public (and it cannot be public, after the next commit).

Author: apoelstra

src/builtins.rs renamed to src/compile/builtins.rs

@@ -1,18 +1,20 @@
 //! Compile the parsed ast into a simplicity program
 
+mod builtins;
+
 use std::sync::Arc;
 
 use either::Either;
 use simplicity::jet::Elements;
 use simplicity::node::{CoreConstructible as _, JetConstructible as _};
 use simplicity::{Cmr, FailEntropy};
 
+use self::builtins::array_fold;
 use crate::array::{BTreeSlice, Partition};
 use crate::ast::{
     Call, CallName, Expression, ExpressionInner, Match, Program, SingleExpression,
     SingleExpressionInner, Statement,
 };
-use crate::builtins::array_fold;
 use crate::debug::CallTracker;
 use crate::error::{Error, RichError, Span, WithSpan};
 use crate::named::{self, CoreExt, PairBuilder};

src/compile/mod.rs

@@ -4,7 +4,6 @@ pub type ProgNode = Arc<named::ConstructNode<Elements>>;
 
 pub mod array;
 pub mod ast;
-pub mod builtins;
 pub mod compile;
 pub mod debug;
 pub mod dummy_env;