Basic string and binary processing

- strings are now made of graphemes
- char is no longer a literal type
- preliminary binary support
- added implicit extraction methods for primitives
- added explicit extraction method for atoms

Nothing has been tested yet

src/foreign_macros/atomic_impl.rs

@@ -63,7 +63,6 @@ use crate::Primitive;
 /// atomic_redirect!(InternalToString, expr_inst);
 /// atomic_impl!(InternalToString, |Self { expr_inst }: &Self, _|{
 ///   with_lit(expr_inst, |l| Ok(match l {
-///     Literal::Char(c) => c.to_string(),
 ///     Literal::Uint(i) => i.to_string(),
 ///     Literal::Num(n) => n.to_string(),
 ///     Literal::Str(s) => s.clone(),

src/foreign_macros/define_fn.rs

@@ -65,7 +65,6 @@ use crate::write_fn_step;
 ///   /// Convert a literal to a string using Rust's conversions for floats,
 ///   /// chars and uints respectively
 ///   ToString = |x| with_lit(x, |l| Ok(match l {
-///     Literal::Char(c) => c.to_string(),
 ///     Literal::Uint(i) => i.to_string(),
 ///     Literal::Num(n) => n.to_string(),
 ///     Literal::Str(s) => s.clone(),
@@ -147,12 +146,12 @@ macro_rules! define_fn {
     $crate::write_fn_step!(
       $name
       {
-        $( $arg_prev:ident : $typ_prev:ty ),*
+        $( $arg_prev : $typ_prev ),*
       }
-      [< $name $arg0:upper >]
+      [< $name $arg0:camel >]
       where $arg0:$typ0 $( = $xname => $parse0 )? ;
     );
-    $crate::define_fn!(@MIDDLE $xname [< $name $arg0:upper >] ($body)
+    $crate::define_fn!(@MIDDLE $xname [< $name $arg0:camel >] ($body)
       (
         $( ($arg_prev: $typ_prev) )*
         ($arg0: $typ0)

src/foreign_macros/write_fn_step.rs

@@ -18,7 +18,10 @@ use crate::interpreted::ExprInst;
 /// discussed below. The newly bound names (here `s` and `i` before `=`) can
 /// also receive type annotations.
 ///
-/// ```
+/// ```no_run
+/// // FIXME this is a very old example that wouldn't compile now
+/// use unicode_segmentation::UnicodeSegmentation;
+/// 
 /// use orchidlang::{write_fn_step, Literal, Primitive};
 /// use orchidlang::interpreted::Clause;
 /// use orchidlang::stl::litconv::{with_str, with_uint};
@@ -36,8 +39,8 @@ use crate::interpreted::ExprInst;
 ///   CharAt0 { s: String }
 ///   i = x => with_uint(x, Ok);
 ///   {
-///     if let Some(c) = s.chars().nth(*i as usize) {
-///       Ok(Clause::P(Primitive::Literal(Literal::Char(c))))
+///     if let Some(c) = s.graphemes(true).nth(*i as usize) {
+///       Ok(Literal::Char(c.to_string()).into())
 ///     } else {
 ///       RuntimeError::fail(
 ///         "Character index out of bounds".to_string(),