Split up parser

The structure mostly follows the ast structure, with some slight
changes. Each parser submodule documents which ast submodule it
corresponds to.

This parser is not yet complete, and I have yet to go through its
modules one-by-one to fix and complete them.

src/parser/var.rs

@@ -0,0 +1,86 @@
+//! Corresponds to `ast::var`.
+
+use chumsky::prelude::*;
+
+use crate::ast::{Expr, Var};
+
+use super::basic::{ident, space, Error};
+
+fn var_access(
+    expr: impl Parser<char, Expr, Error = Error> + Clone,
+) -> impl Parser<char, Var, Error = Error> {
+    just("[")
+        .ignore_then(space())
+        .then(expr)
+        .then(space())
+        .then_ignore(just("]"))
+        .map_with_span(|((s0, index), s1), span| Var::Access {
+            s0,
+            index: Box::new(index),
+            s1,
+            span,
+        })
+}
+
+fn var_assign(
+    expr: impl Parser<char, Expr, Error = Error> + Clone,
+) -> impl Parser<char, Var, Error = Error> {
+    let local = text::keyword("local").ignore_then(space()).or_not();
+
+    local
+        .then_ignore(just("["))
+        .then(space())
+        .then(expr.clone())
+        .then(space())
+        .then_ignore(just("]"))
+        .then(space())
+        .then_ignore(just("="))
+        .then(space())
+        .then(expr)
+        .map_with_span(
+            |((((((local, s0), index), s1), s2), s3), value), span| Var::Assign {
+                local,
+                s0,
+                index: Box::new(index),
+                s1,
+                s2,
+                s3,
+                value: Box::new(value),
+                span,
+            },
+        )
+}
+
+fn var_assign_ident(
+    expr: impl Parser<char, Expr, Error = Error> + Clone,
+) -> impl Parser<char, Var, Error = Error> {
+    let local = text::keyword("local").ignore_then(space()).or_not();
+
+    local
+        .then(ident())
+        .then(space())
+        .then_ignore(just("="))
+        .then(space())
+        .then(expr)
+        .map_with_span(
+            |((((local, name), s0), s1), value), span| Var::AssignIdent {
+                local,
+                name,
+                s0,
+                s1,
+                value: Box::new(value),
+                span,
+            },
+        )
+}
+
+pub fn var(
+    expr: impl Parser<char, Expr, Error = Error> + Clone,
+) -> impl Parser<char, Var, Error = Error> {
+    let access = var_access(expr.clone());
+    let assign = var_assign(expr.clone());
+    let access_ident = ident().map(Var::AccessIdent);
+    let assign_ident = var_assign_ident(expr);
+
+    assign.or(access).or(assign_ident).or(access_ident)
+}