Add parser for 'Pair' pattern

  And a few more tests along the way for others. Note that it is important here that we try to parse for a 'Pair' BEFORE we try to parse for a constructor pattern. Because the latter would swallow any Pair pattern.

crates/aiken-lang/src/parser/pattern/mod.rs

@@ -4,30 +4,32 @@ mod constructor;
 mod discard;
 mod int;
 mod list;
+mod pair;
 mod tuple;
 mod var;
 
+use crate::{
+    ast::UntypedPattern,
+    parser::{error::ParseError, token::Token},
+};
 pub use constructor::parser as constructor;
 pub use discard::parser as discard;
 pub use int::parser as int;
 pub use list::parser as list;
+pub use pair::parser as pair;
 pub use tuple::parser as tuple;
 pub use var::parser as var;
 
-use crate::{
-    ast::UntypedPattern,
-    parser::{error::ParseError, token::Token},
-};
-
 pub fn parser() -> impl Parser<Token, UntypedPattern, Error = ParseError> {
-    recursive(|expression| {
+    recursive(|pattern| {
         choice((
-            var(expression.clone()),
-            constructor(expression.clone()),
+            var(pattern.clone()),
+            pair(pattern.clone()),
+            constructor(pattern.clone()),
             discard(),
             int(),
-            tuple(expression.clone()),
-            list(expression),
+            tuple(pattern.clone()),
+            list(pattern),
         ))
         .then(
             just(Token::As)
@@ -47,3 +49,63 @@ pub fn parser() -> impl Parser<Token, UntypedPattern, Error = ParseError> {
         })
     })
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::assert_pattern;
+
+    #[test]
+    fn pattern_var() {
+        assert_pattern!("foo");
+    }
+
+    #[test]
+    fn pattern_discard_unnamed() {
+        assert_pattern!("_");
+    }
+
+    #[test]
+    fn pattern_discard_named() {
+        assert_pattern!("_foo");
+    }
+
+    #[test]
+    fn pattern_pair_discards() {
+        assert_pattern!("Pair(_, _)");
+    }
+
+    #[test]
+    fn pattern_pair_explicit_depth_1() {
+        assert_pattern!("Pair(14, True)");
+    }
+
+    #[test]
+    fn pattern_pair_explicit_depth_2() {
+        assert_pattern!("Pair([1,2,3], Pair((14, 42), _))");
+    }
+
+    #[test]
+    fn pattern_constructor_no_labels() {
+        assert_pattern!("Foo(a, b)");
+    }
+
+    #[test]
+    fn pattern_constructor_labels() {
+        assert_pattern!("Foo { a, b }");
+    }
+
+    #[test]
+    fn pattern_constructor_spread() {
+        assert_pattern!("Foo { a, .. }");
+    }
+
+    #[test]
+    fn pattern_constructor_pair_interleaved() {
+        assert_pattern!("Foo(a, Pair(1, 2))");
+    }
+
+    #[test]
+    fn pattern_list_spread() {
+        assert_pattern!("[head, ..]");
+    }
+}

crates/aiken-lang/src/parser/pattern/pair.rs

@@ -0,0 +1,25 @@
+use crate::{
+    ast::UntypedPattern,
+    builtins::PAIR,
+    parser::{error::ParseError, token::Token},
+};
+use chumsky::prelude::*;
+
+pub fn parser(
+    pattern: Recursive<'_, Token, UntypedPattern, ParseError>,
+) -> impl Parser<Token, UntypedPattern, Error = ParseError> + '_ {
+    select! {Token::UpName { name } if name == PAIR => name}
+        .ignore_then(choice((
+            just(Token::LeftParen),
+            just(Token::NewLineLeftParen),
+        )))
+        .then(pattern.clone())
+        .then_ignore(just(Token::Comma))
+        .then(pattern.clone())
+        .then_ignore(just(Token::RightParen))
+        .map_with_span(|((_name, fst), snd), location| UntypedPattern::Pair {
+            fst: Box::new(fst),
+            snd: Box::new(snd),
+            location,
+        })
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_constructor_labels.snap

@@ -0,0 +1,35 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\nFoo { a, b }"
+---
+Constructor {
+    is_record: true,
+    location: 0..12,
+    name: "Foo",
+    arguments: [
+        CallArg {
+            label: Some(
+                "a",
+            ),
+            location: 6..7,
+            value: Var {
+                location: 6..7,
+                name: "a",
+            },
+        },
+        CallArg {
+            label: Some(
+                "b",
+            ),
+            location: 9..10,
+            value: Var {
+                location: 9..10,
+                name: "b",
+            },
+        },
+    ],
+    module: None,
+    constructor: (),
+    with_spread: false,
+    tipo: (),
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_constructor_no_labels.snap

@@ -0,0 +1,31 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\nFoo(a, b)"
+---
+Constructor {
+    is_record: false,
+    location: 0..9,
+    name: "Foo",
+    arguments: [
+        CallArg {
+            label: None,
+            location: 4..5,
+            value: Var {
+                location: 4..5,
+                name: "a",
+            },
+        },
+        CallArg {
+            label: None,
+            location: 7..8,
+            value: Var {
+                location: 7..8,
+                name: "b",
+            },
+        },
+    ],
+    module: None,
+    constructor: (),
+    with_spread: false,
+    tipo: (),
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_constructor_pair_interleaved.snap

@@ -0,0 +1,44 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\nFoo(a, Pair(1, 2))"
+---
+Constructor {
+    is_record: false,
+    location: 0..18,
+    name: "Foo",
+    arguments: [
+        CallArg {
+            label: None,
+            location: 4..5,
+            value: Var {
+                location: 4..5,
+                name: "a",
+            },
+        },
+        CallArg {
+            label: None,
+            location: 7..17,
+            value: Pair {
+                location: 7..17,
+                fst: Int {
+                    location: 12..13,
+                    value: "1",
+                    base: Decimal {
+                        numeric_underscore: false,
+                    },
+                },
+                snd: Int {
+                    location: 15..16,
+                    value: "2",
+                    base: Decimal {
+                        numeric_underscore: false,
+                    },
+                },
+            },
+        },
+    ],
+    module: None,
+    constructor: (),
+    with_spread: false,
+    tipo: (),
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_constructor_spread.snap

@@ -0,0 +1,25 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\nFoo { a, .. }"
+---
+Constructor {
+    is_record: true,
+    location: 0..13,
+    name: "Foo",
+    arguments: [
+        CallArg {
+            label: Some(
+                "a",
+            ),
+            location: 6..7,
+            value: Var {
+                location: 6..7,
+                name: "a",
+            },
+        },
+    ],
+    module: None,
+    constructor: (),
+    with_spread: true,
+    tipo: (),
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_discard_named.snap

@@ -0,0 +1,8 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\n_foo"
+---
+Discard {
+    name: "_foo",
+    location: 0..4,
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_discard_unnamed.snap

@@ -0,0 +1,8 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\n_"
+---
+Discard {
+    name: "_",
+    location: 0..1,
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_list_spread.snap

@@ -0,0 +1,19 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\n[head, ..]"
+---
+List {
+    location: 0..10,
+    elements: [
+        Var {
+            location: 1..5,
+            name: "head",
+        },
+    ],
+    tail: Some(
+        Discard {
+            name: "_",
+            location: 9..10,
+        },
+    ),
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_pair_discards.snap

@@ -0,0 +1,15 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\nPair(_, _)"
+---
+Pair {
+    location: 0..10,
+    fst: Discard {
+        name: "_",
+        location: 5..6,
+    },
+    snd: Discard {
+        name: "_",
+        location: 8..9,
+    },
+}

crates/aiken-lang/src/parser/pattern/snapshots/pattern_pair_explicit_depth_1.snap

@@ -0,0 +1,24 @@
+---
+source: crates/aiken-lang/src/parser/pattern/mod.rs
+description: "Code:\n\nPair(14, True)"
+---
+Pair {
+    location: 0..14,
+    fst: Int {
+        location: 5..7,
+        value: "14",
+        base: Decimal {
+            numeric_underscore: false,
+        },
+    },
+    snd: Constructor {
+        is_record: false,
+        location: 9..13,
+        name: "True",
+        arguments: [],
+        module: None,
+        constructor: (),
+        with_spread: false,
+        tipo: (),
+    },
+}