Add wildcard patterns

This commit adds a special pattern that doesn't bind anything and match
any value, the wildcard pattern `_`. This pattern doesn't force the
value being matched on.

core/src/eval/mod.rs

@@ -1189,9 +1189,6 @@ pub fn subst<C: Cache>(
  RichTerm::new(Term::App(t1, t2), pos)
  }
  Term::Match(data) => {
- let default =
- data.default.map(|d| subst(cache, d, initial_env, env));
-
  let branches = data.branches
  .into_iter()
  .map(|(pat, branch)| {
@@ -1202,7 +1199,7 @@ pub fn subst<C: Cache>(
  })
  .collect();
 
- RichTerm::new(Term::Match(MatchData { branches, default}), pos)
+ RichTerm::new(Term::Match(MatchData { branches }), pos)
  }
  Term::Op1(op, t) => {
  let t = subst(cache, t, initial_env, env);

core/src/parser/grammar.lalrpop

@@ -308,27 +308,13 @@ Applicative: UniTerm = {
  => UniTerm::from(mk_term::op2(op, t1, t2)),
  NOpPre<AsTerm<Atom>>,
  "match" "{" <branches: (MatchCase ",")*> <last: MatchCase?> "}" => {
- let mut default = None;
-
  let branches = branches
  .into_iter()
  .map(|(case, _comma)| case)
  .chain(last)
- .filter_map(|case| match case {
- MatchCase::Normal(pat, branch) => Some((pat, branch)),
- MatchCase::Default(default_branch) => {
- default = Some(default_branch);
- None
- }
- })
  .collect();
 
- UniTerm::from(
- Term::Match(MatchData {
- branches,
- default,
- })
- )
+ UniTerm::from(Term::Match(MatchData { branches }))
  }
 };
 
@@ -578,6 +564,7 @@ PatternDataF<F>: PatternData = {
  ConstantPattern => PatternData::Constant(<>),
  EnumPatternF<F> => PatternData::Enum(<>),
  Ident => PatternData::Any(<>),
+ "_" => PatternData::Wildcard,
 };
 
 // A general pattern.
@@ -888,17 +875,8 @@ UOp: UnaryOp = {
  "enum_get_tag" => UnaryOp::EnumGetTag(),
 }
 
-// It might seem silly that a match case can always be the catch-all case
-// `_ => <exp>`. It would be better to separate between a normal match case and
-// a rule for the catch-call. However, it's then surprisingly annoying to
-// express the rule for "match" such that it's both non-ambiguous and allow an
-// optional trailing comma ",".
-//
-// In the end, it was simpler to just allow the catch-all case to appear
-// anywhere, and then to raise an error in the action code of the "match" rule.
-MatchCase: MatchCase = {
- <pat: Pattern> "=>" <t: Term> => MatchCase::Normal(pat, t),
- "_" "=>" <Term> => MatchCase::Default(<>),
+MatchCase: (Pattern, RichTerm) = {
+ <pat: Pattern> "=>" <t: Term> => (pat, t),
 };
 
 // Infix operators by precedence levels. Lowest levels take precedence over

core/src/parser/utils.rs

@@ -79,13 +79,6 @@ pub enum StringEndDelimiter {
  Special,
 }
 
-/// Distinguish between a normal case `id => exp` and a default case `_ => exp`.
-#[derive(Clone, Debug)]
-pub enum MatchCase {
- Normal(Pattern, RichTerm),
- Default(RichTerm),
-}
-
 /// Left hand side of a record field declaration.
 #[derive(Clone, Debug)]
 pub enum FieldPathElem {

core/src/pretty.rs

@@ -585,6 +585,7 @@ where
 {
  fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
  match self {
+ PatternData::Wildcard => allocator.text("_"),
  PatternData::Any(id) => allocator.as_string(id),
  PatternData::Record(rp) => rp.pretty(allocator),
  PatternData::Enum(evp) => evp.pretty(allocator),
@@ -886,7 +887,6 @@ where
  data.branches
  .iter()
  .map(|(pat, t)| (pat.pretty(allocator), t))
- .chain(data.default.iter().map(|d| (allocator.text("_"), d)))
  .map(|(lhs, t)| docs![
  allocator,
  lhs,

core/src/term/mod.rs

@@ -610,7 +610,6 @@ pub struct MatchData {
  /// Branches of the match expression, where the first component is the pattern on the left hand
  /// side of `=>` and the second component is the body of the branch.
  pub branches: Vec<(Pattern, RichTerm)>,
- pub default: Option<RichTerm>,
 }
 
 /// A type or a contract together with its corresponding label.
@@ -2032,12 +2031,9 @@ impl Traverse<RichTerm> for RichTerm {
  .map(|(pat, t)| t.traverse(f, order).map(|t_ok| (pat, t_ok)))
  .collect();
 
- let default = data.default.map(|t| t.traverse(f, order)).transpose()?;
-
  RichTerm::new(
  Term::Match(MatchData {
  branches: branches?,
- default,
  }),
  pos,
  )
@@ -2210,8 +2206,7 @@ impl Traverse<RichTerm> for RichTerm {
  Term::Match(data) => data
  .branches
  .iter()
- .find_map(|(_pat, t)| t.traverse_ref(f, state))
- .or_else(|| data.default.as_ref().and_then(|t| t.traverse_ref(f, state))),
+ .find_map(|(_pat, t)| t.traverse_ref(f, state)),
  Term::Array(ts, _) => ts.iter().find_map(|t| t.traverse_ref(f, state)),
  Term::OpN(_, ts) => ts.iter().find_map(|t| t.traverse_ref(f, state)),
  Term::Annotated(annot, t) => t

core/src/term/pattern/compile.rs

@@ -252,6 +252,7 @@ impl CompilePart for Pattern {
 impl CompilePart for PatternData {
  fn compile_part(&self, value_id: LocIdent, bindings_id: LocIdent) -> RichTerm {
  match self {
+ PatternData::Wildcard => Term::Var(bindings_id).into(),
  PatternData::Any(id) => {
  // %record_insert% "<id>" value_id bindings_id
  insert_binding(*id, value_id, bindings_id)
@@ -670,31 +671,48 @@ impl Compile for MatchData {
  if self.branches.iter().all(|(pat, _)| {
  matches!(
  pat.data,
- PatternData::Enum(EnumPattern { pattern: None, .. })
+ PatternData::Enum(EnumPattern { pattern: None, .. }) | PatternData::Wildcard
  )
  }) {
- let tags_only = self.branches.into_iter().map(|(pat, body)| {
- let PatternData::Enum(EnumPattern {tag, ..}) = pat.data else {
- panic!("match compilation: just tested that all cases are enum tags, but found a non enum tag pattern");
- };
-
- (tag, body)
- }).collect();
+ // We take the first wildcard pattern as the default case. In theory, we could discard
+ // all the tags coming after the default branch; in practice we expect any sane match
+ // expression to have the default branch at the end, so this isn't a very useful
+ // optimization to care about.
+ let default = self.branches.iter().find_map(|(pat, body)| {
+ if let PatternData::Wildcard = pat.data {
+ Some(body.clone())
+ } else {
+ None
+ }
+ });
+
+ let tags_only = self
+ .branches
+ .into_iter()
+ .filter_map(|(pat, body)| {
+ if let PatternData::Enum(EnumPattern { tag, .. }) = pat.data {
+ Some((tag, body))
+ } else {
+ None
+ }
+ })
+ .collect();
 
  return TagsOnlyMatch {
  branches: tags_only,
- default: self.default,
+ default,
  }
  .compile(value, pos);
  }
 
- let default_branch = self.default.unwrap_or_else(|| {
+ let error_case = RichTerm::new(
  Term::RuntimeError(EvalError::NonExhaustiveMatch {
  value: value.clone(),
  pos,
- })
- .into()
- });
+ }),
+ pos,
+ );
+
  let value_id = LocIdent::fresh();
 
  // The fold block:
@@ -711,45 +729,45 @@ impl Compile for MatchData {
  // else
  // # this primop evaluates body with an environment extended with bindings_id
  // %pattern_branch% body bindings_id
- let fold_block =
- self.branches
-  .into_iter()
-  .rev()
-  .fold(default_branch, |cont, (pat, body)| {
-  let init_bindings_id = LocIdent::fresh();
-  let bindings_id = LocIdent::fresh();
-
-  // inner if block:
-  //
-  // if bindings_id == null then
-  // cont
-  // else
-  // # this primop evaluates body with an environment extended with bindings_id
-  // %pattern_branch% bindings_id body
-  let inner = make::if_then_else(
-  make::op2(BinaryOp::Eq(), Term::Var(bindings_id), Term::Null),
-  cont,
-  mk_app!(
-  make::op1(UnaryOp::PatternBranch(), Term::Var(bindings_id),),
-  body
-  ),
-  );
+ let fold_block = self
+ .branches
+ .into_iter()
+ .rev()
+ .fold(error_case, |cont, (pat, body)| {
+ let init_bindings_id = LocIdent::fresh();
+ let bindings_id = LocIdent::fresh();
+
+ // inner if block:
+ //
+ // if bindings_id == null then
+ // cont
+ // else
+ // # this primop evaluates body with an environment extended with bindings_id
+ // %pattern_branch% bindings_id body
+ let inner = make::if_then_else(
+ make::op2(BinaryOp::Eq(), Term::Var(bindings_id), Term::Null),
+ cont,
+ mk_app!(
+ make::op1(UnaryOp::PatternBranch(), Term::Var(bindings_id),),
+ body
+ ),
+ );
 
- // The two initial chained let-bindings:
- //
- // let init_bindings_id = {} in
- // let bindings_id = <pattern.compile_part(value_id, init_bindings)> in
- // <inner>
+ // The two initial chained let-bindings:
+ //
+ // let init_bindings_id = {} in
+ // let bindings_id = <pattern.compile_part(value_id, init_bindings)> in
+ // <inner>
+ make::let_in(
+ init_bindings_id,
+ Term::Record(RecordData::empty()),
  make::let_in(
- init_bindings_id,
- Term::Record(RecordData::empty()),
- make::let_in(
- bindings_id,
- pat.compile_part(value_id, init_bindings_id),
- inner,
- ),
- )
- });
+ bindings_id,
+ pat.compile_part(value_id, init_bindings_id),
+ inner,
+ ),
+ )
+ });
 
  // let value_id = value in <fold_block>
  make::let_in(value_id, value, fold_block)

core/src/term/pattern/mod.rs

@@ -22,6 +22,9 @@ pub mod compile;
 
 #[derive(Debug, PartialEq, Clone)]
 pub enum PatternData {
+ /// A wildcard pattern, matching any value. As opposed to any, this pattern doesn't bind any
+ /// variable.
+ Wildcard,
  /// A simple pattern consisting of an identifier. Match anything and bind the result to the
  /// corresponding identfier.
  Any(LocIdent),
@@ -215,7 +218,7 @@ pub trait ElaborateContract {
 impl ElaborateContract for PatternData {
  fn elaborate_contract(&self) -> Option<LabeledType> {
  match self {
- PatternData::Any(_) => None,
+ PatternData::Wildcard | PatternData::Any(_) => None,
  PatternData::Record(pat) => pat.elaborate_contract(),
  PatternData::Enum(pat) => pat.elaborate_contract(),
  PatternData::Constant(pat) => pat.elaborate_contract(),

core/src/transform/desugar_destructuring.rs

@@ -136,6 +136,7 @@ impl Desugar for Pattern {
 impl Desugar for PatternData {
  fn desugar(self, destr: RichTerm, body: RichTerm) -> Term {
  match self {
+ PatternData::Wildcard => body.into(),
  // If the pattern is an unconstrained identifier, we just bind it to the value.
  PatternData::Any(id) => Term::Let(id, destr, body, LetAttrs::default()),
  PatternData::Record(pat) => pat.desugar(destr, body),

core/src/transform/free_vars.rs

@@ -95,10 +95,6 @@ impl CollectFreeVars for RichTerm {
 
  free_vars.extend(fresh);
  }
-
- if let Some(default) = &mut data.default {
- default.collect_free_vars(free_vars);
- }
  }
  Term::Op1(_, t) | Term::Sealed(_, t, _) | Term::EnumVariant { arg: t, .. } => {
  t.collect_free_vars(free_vars)
@@ -255,8 +251,8 @@ impl RemoveBindings for PatternData {
  PatternData::Enum(enum_variant_pat) => {
  enum_variant_pat.remove_bindings(working_set);
  }
- // A constant pattern doesn't bind any variable.
- PatternData::Constant(_) => (),
+ // A wildcard pattern or a constant pattern doesn't bind any variable.
+ PatternData::Wildcard | PatternData::Constant(_) => (),
  }
  }
 }

core/src/typ.rs

@@ -1030,26 +1030,35 @@ impl Subcontract for EnumRows {
  }
  }
 
- let default = if let Some(var) = tail_var {
- mk_app!(
- mk_term::op2(
- BinaryOp::ApplyContract(),
- get_var_contract(&vars, var.ident(), var.pos)?,
- mk_term::var(label_arg)
+ let (default, default_pos) = if let Some(var) = tail_var {
+ (
+ mk_app!(
+ mk_term::op2(
+ BinaryOp::ApplyContract(),
+ get_var_contract(&vars, var.ident(), var.pos)?,
+ mk_term::var(label_arg)
+ ),
+ mk_term::var(value_arg)
  ),
- mk_term::var(value_arg)
+ var.pos,
  )
  } else {
- mk_app!(internals::enum_fail(), mk_term::var(label_arg))
+ (
+ mk_app!(internals::enum_fail(), mk_term::var(label_arg)),
+ TermPos::None,
+ )
  };
 
- let match_expr = mk_app!(
- Term::Match(MatchData {
- branches,
- default: Some(default)
- }),
- mk_term::var(value_arg)
- );
+ branches.push((
+ Pattern {
+ data: PatternData::Wildcard,
+ alias: None,
+ pos: default.pos,
+ },
+ default,
+ ));
+
+ let match_expr = mk_app!(Term::Match(MatchData { branches }), mk_term::var(value_arg));
 
  let case = mk_fun!(label_arg, value_arg, match_expr);
  Ok(mk_app!(internals::enumeration(), case))