feat: finish moving definitions and start exprs

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

@@ -0,0 +1,3 @@
+mod sequence;
+
+pub use sequence::parser as sequence;

crates/aiken-lang/src/parser/expr/sequence.rs

@@ -0,0 +1,36 @@
+use chumsky::prelude::*;
+
+use crate::{
+    ast::TraceKind,
+    expr::UntypedExpr,
+    parser::{error::ParseError, token::Token},
+};
+
+pub fn parser() -> impl Parser<Token, UntypedExpr, Error = ParseError> {
+    recursive(|r| {
+        choice((
+            just(Token::Trace)
+                .ignore_then(expr_parser(r.clone()))
+                .then(r.clone())
+                .map_with_span(|(text, then_), span| UntypedExpr::Trace {
+                    kind: TraceKind::Trace,
+                    location: span,
+                    then: Box::new(then_),
+                    text: Box::new(flexible_string_literal(text)),
+                }),
+            just(Token::ErrorTerm)
+                .ignore_then(expr_parser(r.clone()).or_not())
+                .map_with_span(|reason, span| {
+                    UntypedExpr::error(span, reason.map(flexible_string_literal))
+                }),
+            just(Token::Todo)
+                .ignore_then(expr_parser(r.clone()).or_not())
+                .map_with_span(|reason, span| {
+                    UntypedExpr::todo(span, reason.map(flexible_string_literal))
+                }),
+            expr_parser(r.clone())
+                .then(r.repeated())
+                .foldl(|current, next| current.append_in_sequence(next)),
+        ))
+    })
+}