feat: Add is_none

There was no way to assert that an option value is None, so I add
is_none which returns true if the value is None. Rust seems to have
decided against unwrap_none, so I will not go down that path.

rust-lang/rust#62633

assert!(is_none(x)) might produce slightly larger Simplicity expressions
than a hypothetical unwrap_none(x), but I will not try to prematurely
optimize any Simplicity code here. A future version of the Simfony
compiler might detect assert! + is_none and produce an optimized
Simplicity expression accordingly.

src/ast.rs

@@ -233,6 +233,8 @@ pub enum CallName {
     UnwrapLeft(ResolvedType),
     /// [`Either::unwrap_right`].
     UnwrapRight(ResolvedType),
+    /// [`Option::is_none`].
+    IsNone(ResolvedType),
     /// [`Option::unwrap`].
     Unwrap,
     /// [`assert`].
@@ -900,6 +902,22 @@ impl AbstractSyntaxTree for Call {
                     scope,
                 )?])
             }
+            CallName::IsNone(some_ty) => {
+                if from.args.len() != 1 {
+                    return Err(Error::InvalidNumberOfArguments(1, from.args.len()))
+                        .with_span(from);
+                }
+                let out_ty = ResolvedType::boolean();
+                if ty != &out_ty {
+                    return Err(Error::ExpressionTypeMismatch(ty.clone(), out_ty)).with_span(from);
+                }
+                let arg_ty = ResolvedType::option(some_ty);
+                Arc::from([Expression::analyze(
+                    from.args.first().unwrap(),
+                    &arg_ty,
+                    scope,
+                )?])
+            }
             CallName::Unwrap => {
                 let args_ty = ResolvedType::option(ty.clone());
                 if from.args.len() != 1 {
@@ -998,6 +1016,9 @@ impl AbstractSyntaxTree for CallName {
                 .resolve(left_ty)
                 .map(Self::UnwrapRight)
                 .with_span(from),
+            parse::CallName::IsNone(some_ty) => {
+                scope.resolve(some_ty).map(Self::IsNone).with_span(from)
+            }
             parse::CallName::Unwrap => Ok(Self::Unwrap),
             parse::CallName::Assert => Ok(Self::Assert),
             parse::CallName::TypeCast(target) => {

src/compile.rs

@@ -302,6 +302,11 @@ impl Call {
                 let get_inner = ProgNode::assertr_take(fail_cmr, &ProgNode::iden());
                 ProgNode::comp(&right_and_unit, &get_inner).with_span(self)
             }
+            CallName::IsNone(..) => {
+                let sum_and_unit = ProgNode::pair_unit(&args);
+                let is_right = ProgNode::case_true_false();
+                ProgNode::comp(&sum_and_unit, &is_right).with_span(self)
+            }
             CallName::Assert => {
                 let jet = ProgNode::jet(Elements::Verify);
                 ProgNode::comp(&args, &jet).with_span(self)

src/minimal.pest

@@ -56,10 +56,11 @@ false_expr        = @{ "false" }
 true_expr         = @{ "true" }
 unwrap_left       =  { "unwrap_left::<" ~ ty ~ ">" }
 unwrap_right      =  { "unwrap_right::<" ~ ty ~ ">" }
+is_none           =  { "is_none::<" ~ ty ~ ">" }
 unwrap            = @{ "unwrap" }
 assert            = @{ "assert!" }
 type_cast         =  { "<" ~ ty ~ ">::into" }
-call_name         =  { jet | unwrap_left | unwrap_right | unwrap | assert | type_cast | function_name }
+call_name         =  { jet | unwrap_left | unwrap_right | is_none | unwrap | assert | type_cast | function_name }
 call_args         =  { "(" ~ (expression ~ ("," ~ expression)*)? ~ ")" }
 call_expr         =  { call_name ~ call_args }
 unsigned_decimal  = @{ (ASCII_DIGIT | "_")+ }

src/named.rs

@@ -287,6 +287,16 @@ pub trait CoreExt: CoreConstructible + Sized {
     fn assertr_drop(cmr: Cmr, right: &Self) -> Self {
         Self::assertr(cmr, &Self::drop_(right)).unwrap()
     }
+
+    /// `case false true` always type-checks.
+    fn case_false_true() -> Self {
+        Self::case(&Self::bit_false(), &Self::bit_true()).unwrap()
+    }
+
+    /// `case true false` always type-checks.
+    fn case_true_false() -> Self {
+        Self::case(&Self::bit_true(), &Self::bit_false()).unwrap()
+    }
 }
 
 impl<N: CoreConstructible> CoreExt for N {}

src/parse.rs

@@ -278,6 +278,8 @@ pub enum CallName {
     UnwrapRight(AliasedType),
     /// [`Option::unwrap`].
     Unwrap,
+    /// [`Option::is_none`].
+    IsNone(AliasedType),
     /// [`assert`].
     Assert,
     /// Cast from the given source type.
@@ -816,6 +818,10 @@ impl PestParse for CallName {
                 let inner = pair.into_inner().next().unwrap();
                 AliasedType::parse(inner).map(Self::UnwrapRight)
             }
+            Rule::is_none => {
+                let inner = pair.into_inner().next().unwrap();
+                AliasedType::parse(inner).map(Self::IsNone)
+            }
             Rule::unwrap => Ok(Self::Unwrap),
             Rule::assert => Ok(Self::Assert),
             Rule::type_cast => {