cl-parser: Dedicated parsing logic for patterns!

compiler/cl-ast/src/ast.rs

@@ -586,6 +586,7 @@ pub struct MatchArm(pub Pattern, pub Expr);
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub enum Pattern {
     Name(Sym),
+    Path(Path),
     Literal(Literal),
     Rest(Option<Box<Pattern>>),
     Ref(Mutability, Box<Pattern>),

compiler/cl-ast/src/ast_impl/display.rs

@@ -468,6 +468,7 @@ impl Display for Pattern {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
             Pattern::Name(sym) => sym.fmt(f),
+            Pattern::Path(path) => path.fmt(f),
             Pattern::Literal(literal) => literal.fmt(f),
             Pattern::Rest(Some(name)) => write!(f, "..{name}"),
             Pattern::Rest(None) => "..".fmt(f),

compiler/cl-ast/src/ast_impl/weight_of.rs

@@ -338,6 +338,7 @@ impl WeightOf for Pattern {
     fn weight_of(&self) -> usize {
         match self {
             Pattern::Name(s) => size_of_val(s),
+            Pattern::Path(p) => p.weight_of(),
             Pattern::Literal(literal) => literal.weight_of(),
             Pattern::Rest(Some(pattern)) => pattern.weight_of(),
             Pattern::Rest(None) => 0,

compiler/cl-ast/src/ast_visitor/fold.rs

@@ -253,6 +253,7 @@ pub trait Fold {
     fn fold_pattern(&mut self, p: Pattern) -> Pattern {
         match p {
             Pattern::Name(sym) => Pattern::Name(self.fold_sym(sym)),
+            Pattern::Path(path) => Pattern::Path(self.fold_path(path)),
             Pattern::Literal(literal) => Pattern::Literal(self.fold_literal(literal)),
             Pattern::Rest(Some(name)) => Pattern::Rest(Some(self.fold_pattern(*name).into())),
             Pattern::Rest(None) => Pattern::Rest(None),

compiler/cl-ast/src/ast_visitor/walk.rs

@@ -793,6 +793,7 @@ impl Walk for Pattern {
     fn children<'a, V: Visit<'a>>(&'a self, v: &mut V) {
         match self {
             Pattern::Name(sym) => sym.visit_in(v),
+            Pattern::Path(path) => path.visit_in(v),
             Pattern::Literal(literal) => literal.visit_in(v),
             Pattern::Rest(pattern) => pattern.visit_in(v),
             Pattern::Ref(mutability, pattern) => {

compiler/cl-interpret/src/pattern.rs

@@ -14,8 +14,9 @@ use std::collections::{HashMap, VecDeque};
 pub fn variables(pat: &Pattern) -> Vec<&Sym> {
     fn patvars<'p>(set: &mut Vec<&'p Sym>, pat: &'p Pattern) {
         match pat {
-            Pattern::Name(name) if &**name == "_" => {}
+            Pattern::Name(name) if name.to_ref() == "_" => {}
             Pattern::Name(name) => set.push(name),
+            Pattern::Path(_) => {}
             Pattern::Literal(_) => {}
             Pattern::Rest(Some(pattern)) => patvars(set, pattern),
             Pattern::Rest(None) => {}

compiler/cl-parser/src/parser.rs

@@ -1093,10 +1093,94 @@ impl Parse<'_> for Return {
     }
 }
 
+fn pathpattern(p: &mut Parser<'_>) -> PResult<Pattern> {
+    const P: Parsing = Parsing::Pattern;
+    let name = Path::parse(p)?;
+
+    let struct_members = |p: &mut Parser| {
+        let name = p.parse()?;
+        let pat = if p.match_type(TokenKind::Colon, P).is_ok() {
+            Some(p.parse()?)
+        } else {
+            None
+        };
+        Ok((name, pat))
+    };
+
+    Ok(match p.peek_kind(Parsing::Pattern)? {
+        TokenKind::LCurly => Pattern::Struct(
+            name,
+            delim(
+                sep(struct_members, TokenKind::Comma, TokenKind::RCurly, P),
+                CURLIES,
+                P,
+            )(p)?,
+        ),
+        TokenKind::LParen => Pattern::TupleStruct(
+            name,
+            delim(
+                sep(Parse::parse, TokenKind::Comma, TokenKind::RParen, P),
+                PARENS,
+                P,
+            )(p)?,
+        ),
+        _ => name
+            .as_sym()
+            .map(Pattern::Name)
+            .unwrap_or(Pattern::Path(name)),
+    })
+}
+
 impl Parse<'_> for Pattern {
     fn parse(p: &mut Parser<'_>) -> PResult<Self> {
-        let value = prec::expr(p, prec::Precedence::Pattern.level())?;
-        Pattern::try_from(value).map_err(|e| p.error(InvalidPattern(e.into()), Parsing::Pattern))
+        const P: Parsing = Parsing::Pattern;
+        Ok(match p.peek_kind(P)? {
+            // Name, Path, Struct, TupleStruct
+            TokenKind::Identifier => pathpattern(p)?,
+            // Literal
+            TokenKind::Literal => Pattern::Literal(p.parse()?),
+            // Rest
+            TokenKind::DotDot => {
+                p.consume_peeked();
+                if matches!(
+                    p.peek_kind(P),
+                    Ok(TokenKind::Identifier | TokenKind::Literal)
+                ) {
+                    Pattern::Rest(Some(p.parse()?))
+                } else {
+                    Pattern::Rest(None)
+                }
+            }
+            // Ref
+            TokenKind::Amp => {
+                p.consume_peeked();
+                Pattern::Ref(p.parse()?, p.parse()?)
+            }
+            // Ref(Ref)
+            TokenKind::AmpAmp => {
+                p.consume_peeked();
+                Pattern::Ref(
+                    Mutability::Not,
+                    Box::new(Pattern::Ref(p.parse()?, p.parse()?)),
+                )
+            }
+            // Tuple
+            TokenKind::LParen => Pattern::Tuple(delim(
+                sep(Parse::parse, TokenKind::Comma, TokenKind::RParen, P),
+                PARENS,
+                P,
+            )(p)?),
+            // Array
+            TokenKind::LBrack => Pattern::Array(delim(
+                sep(Parse::parse, TokenKind::Comma, TokenKind::RBrack, P),
+                BRACKETS,
+                P,
+            )(p)?),
+            _ => {
+                let bad_expr = p.parse()?;
+                Err(p.error(ErrorKind::InvalidPattern(bad_expr), P))?
+            }
+        })
     }
 }
 

compiler/cl-parser/src/parser/prec.rs

@@ -286,7 +286,6 @@ fn structor_body(p: &mut Parser, to: Path) -> PResult<Structor> {
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub enum Precedence {
     Assign,
-    Pattern,   // A pattern can contain a structor
     Structor,  // A structor is never a valid conditional
     Condition, // Anything that syntactically needs a block following it
     Logic,

compiler/cl-repl/examples/to_c.rs

@@ -508,6 +508,7 @@ pub mod clangify {
             // TODO: Pattern match desugaring!!!
             match self {
                 Pattern::Name(name) => y.p(name),
+                Pattern::Path(path) => y.p(path),
                 Pattern::Literal(literal) => y.p(literal),
                 Pattern::Rest(name) => y.p("..").p(name),
                 Pattern::Ref(mutability, pattern) => y.p("&").p(mutability).p(pattern),

compiler/cl-repl/examples/yaml.rs

@@ -428,6 +428,7 @@ pub mod yamlify {
         fn yaml(&self, y: &mut Yamler) {
             match self {
                 Pattern::Name(name) => y.value(name),
+                Pattern::Path(path) => y.value(path),
                 Pattern::Literal(literal) => y.value(literal),
                 Pattern::Rest(name) => y.pair("Rest", name),
                 Pattern::Ref(mutability, pattern) => y.yaml(mutability).pair("Pat", pattern),

compiler/cl-typeck/src/stage/infer/inference.rs

@@ -519,6 +519,11 @@ impl<'a> Inference<'a> for Pattern {
                 e.at = node;
                 Ok(node)
             }
+            Pattern::Path(path) => {
+                // Evaluating a path pattern puts type constraints on the scrutinee
+                path.evaluate(e.table, e.at)
+                    .map_err(|_| InferenceError::NotFound(path.clone()))
+            }
             Pattern::Literal(literal) => literal.infer(e),
             Pattern::Rest(Some(pat)) => pat.infer(e), // <-- glaring soundness holes
             Pattern::Rest(_) => todo!("Fix glaring soundness holes in pattern"),