From 8331e4f341d23199616710ea2a28108f53afd7d6 Mon Sep 17 00:00:00 2001
From: Alex Bethel <abethel@cs.nmt.edu>
Date: Sun, 7 Aug 2022 14:04:35 -0500
Subject: [PATCH] Parse all pattern types

---
 axc/src/parser.rs | 97 +++++++++++++++++++++++++++++++++++++++++------
 axc/src/syntax.rs | 26 ++++++-------
 2 files changed, 97 insertions(+), 26 deletions(-)

diff --git a/axc/src/parser.rs b/axc/src/parser.rs
index c007beb..37360b8 100644
--- a/axc/src/parser.rs
+++ b/axc/src/parser.rs
@@ -541,22 +541,95 @@ fn parse_record_type(
 }
 
 fn parse_pattern(m: &ParserMeta) -> impl Parser<char, Pattern, Error = Simple<char>> {
-    // TODO: add all the patterns
-    choice((parse_capture_pattern(m),))
+    recursive(|rec| {
+        choice((
+            parse_ignore_pattern(m),
+            parse_capture_pattern(m),
+            parse_literal_pattern(m),
+            parse_tuple_pattern(m, rec.clone()),
+            parse_record_pattern(m, rec.clone()),
+        ))
+        .repeated()
+        .at_least(1)
+        .map(|pats| {
+            pats.into_iter()
+                .reduce(|l, r| Pattern::Destructure(Box::new(l), Box::new(r)))
+                .unwrap()
+        })
+        .then(
+            just(':')
+                .then(whitespace())
+                .ignore_then(parse_type(m))
+                .or_not(),
+        )
+        .map(|(pat, typ)| match typ {
+            Some(typ) => Pattern::TypeAnnotated {
+                pat: Box::new(pat),
+                typ: Box::new(typ),
+            },
+            None => pat,
+        })
+    })
+}
+
+fn parse_ignore_pattern(_m: &ParserMeta) -> impl Parser<char, Pattern, Error = Simple<char>> {
+    keyword("_").then_ignore(whitespace()).to(Pattern::Ignore)
 }
 
 fn parse_capture_pattern(_m: &ParserMeta) -> impl Parser<char, Pattern, Error = Simple<char>> {
-    ident()
-        .try_map(|iden: String, span| {
-            if iden.starts_with(|c: char| c.is_lowercase()) {
-                Ok(iden)
+    ident().then_ignore(whitespace()).map(Pattern::Capture)
+}
+
+fn parse_tuple_pattern(
+    _m: &ParserMeta,
+    rec: impl Parser<char, Pattern, Error = Simple<char>>,
+) -> impl Parser<char, Pattern, Error = Simple<char>> {
+    rec.separated_by(just(',').then(whitespace()))
+        .allow_trailing()
+        .delimited_by(just('(').then(whitespace()), just(')').then(whitespace()))
+        .map(|pats| {
+            if pats.len() == 1 {
+                // `(Int)` is the same as `Int`
+                pats.into_iter().next().unwrap()
             } else {
-                Err(Simple::custom(
-                    span,
-                    "capture must start with lowercase letter",
-                ))
+                Pattern::Tuple(pats)
             }
         })
-        .then_ignore(whitespace())
-        .map(Pattern::Exact)
+}
+
+fn parse_record_pattern(
+    _m: &ParserMeta,
+    rec: impl Parser<char, Pattern, Error = Simple<char>>,
+) -> impl Parser<char, Pattern, Error = Simple<char>> {
+    let item = ident().then_ignore(whitespace()).then(
+        just(':')
+            .ignore_then(whitespace())
+            .ignore_then(rec)
+            .or_not(),
+    );
+
+    let items = item
+        .separated_by(just(',').then(whitespace()))
+        .allow_trailing();
+
+    let ellipsis = just("...")
+        .ignore_then(whitespace())
+        .or_not()
+        .map(|ellipsis| ellipsis.is_some());
+
+    items
+        .then(ellipsis)
+        .delimited_by(just('{').then(whitespace()), just('}').then(whitespace()))
+        .map(|(members, inexhaustive)| Pattern::Record {
+            members,
+            inexhaustive,
+        })
+}
+
+fn parse_literal_pattern(m: &ParserMeta) -> impl Parser<char, Pattern, Error = Simple<char>> {
+    // TODO: factor out literal parsing so we don't have to do this ugly `unreachable` stuff.
+    parse_literal(m).map(|e| match e {
+        Expr::Literal(lit) => Pattern::Literal(lit),
+        _ => unreachable!(),
+    })
 }
diff --git a/axc/src/syntax.rs b/axc/src/syntax.rs
index 2ab0cf5..90e71da 100644
--- a/axc/src/syntax.rs
+++ b/axc/src/syntax.rs
@@ -215,6 +215,15 @@ pub enum Pattern {
     /// `(a, b)`
     Tuple(Vec<Pattern>),
 
+    /// `{a: x, b: y}`
+    Record {
+        /// The named members of the record, in order of occurrence.
+        members: Vec<(String, Option<Pattern>)>,
+
+        /// Whether the record ends with "...", for ignoring unlisted elements.
+        inexhaustive: bool,
+    },
+
     /// `a: String`
     TypeAnnotated {
         /// The pattern being annotated.
@@ -224,11 +233,10 @@ pub enum Pattern {
         typ: Box<Type>,
     },
 
-    /// `Foo`
-    Exact(String),
-
     /// `Foo { a: x, b: y, ... }`
-    Destructure(String, Record),
+    // Note that the left side here *must* be just one word, semantically; but we let it be a
+    // Pattern to make parsing easier.
+    Destructure(Box<Pattern>, Box<Pattern>),
 
     /// `_`
     Ignore,
@@ -237,16 +245,6 @@ pub enum Pattern {
     Literal(Literal),
 }
 
-/// Record syntax blocks, e.g., "{a: b, c: d, ...}".
-#[derive(Clone, Debug)]
-pub struct Record {
-    /// The named members of the record, in order of occurrence.
-    pub members: Vec<(String, Expr)>,
-
-    /// Whether the record ends with "..."; this allows ignoring blocks.
-    pub inexhaustive: bool,
-}
-
 /// Literal values included in source code.
 #[derive(Clone, Debug)]
 pub enum Literal {