add let-pattern

kernel/let-pattern.ay

@@ -0,0 +1,24 @@
+use(require("core"))
+use(require("define"))
+use(require("patterns"))
+
+require("atomy/bootstrap")
+
+let-pattern = class:
+  def(initialize(@body, @patterns)) {}
+
+  def(bytecode(gen, mod)):
+    new = Atomy Module new: use(mod)
+
+    @patterns each [`(~pat = ~exp)]:
+      definer = Atomy Bootstrap pattern-definer(
+        Atomy Grammar AST QuasiQuote new(pat)
+        exp
+      )
+
+      new evaluate(definer, new compile-context)
+
+    new compile(gen, @body)
+
+macro(let-pattern(~*ms): ~*body):
+  let-pattern new(`(do: ~*body), ms)

spec/kernel/let_pattern_spec.rb

@@ -0,0 +1,27 @@
+require "spec_helper"
+
+require "atomy/codeloader"
+
+describe "let-pattern kernel" do
+  subject { Atomy::Module.new { use(require("let-pattern")) } }
+
+  it "defines the given pattern for the duration of the body" do
+    expect(subject.evaluate(seq(<<EOF))).to eq(5)
+let-pattern(Foo = pattern('5)):
+  Foo = 5
+EOF
+
+    expect { subject.evaluate(seq(<<EOF)) }.to raise_error(Atomy::PatternMismatch)
+let-pattern(Foo = pattern('5)):
+  Foo = 6
+EOF
+  end
+
+  it "has the pattern in-scope of each other" do
+    expect(subject.evaluate(seq(<<EOF))).to eq(5)
+let-pattern(Foo = pattern('5), Bar = pattern(`(baz & Foo))):
+  Bar = 5
+  baz
+EOF
+  end
+end