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+(defpackage #:sarcasm.ast
+  (:use #:cl)
+  (:import-from #:sarcasm.util #:def/class)
+  (:local-nicknames
+   (#:a #:alexandria-2)
+   (#:util #:sarcasm.util)))
+
+(in-package #:sarcasm.ast)
+
+;;; TYPES
+
+
+
+(deftype i32 ()
+  '(integer 0 #.(expt 2 32)))
+
+(deftype i64 ()
+  '(integer 0 #. (expt 2 64)))
+
+(deftype f32 ()
+  'single-float)
+
+(deftype f64 ()
+  'double-float)
+
+(deftype numtype ()
+  '(or i32 i64 f32 f64))
+
+(deftype typeidx ()
+  'i32)
+
+(deftype vectype ()
+  '(bit-vector 128))
+
+(deftype funcref ()
+  't)
+
+(deftype externref ()
+  't)
+
+(deftype reftype ()
+  '(or funcref externref))
+
+(deftype valtype ()
+  '(or numtype vectype reftype))
+
+(defun stack-effect-type-p (thing)
+  "A stack effect type is a two element list of lists of keywords.
+
+It describes the types of values consumed off the stack and returned
+to the stack by instructions."
+  (and (listp thing)
+       (= 2 (length thing))
+       (listp (first thing))
+       (listp (second thing))
+       (every #'keywordp (first thing))
+       (every #'keywordp (second thing))))
+
+(deftype stack-effect-type ()
+  "This is not part of the standard grammar, but appears implicitly in
+the WASM table of instructions found
+
+ https://webassembly.github.io/spec/core/appendix/index-instructions.html
+
+In the `Type` column."
+  '(satisfies stack-effect-type-p))
+
+;;; MODULE-STRUCTURES
+
+(def/class instr ()
+  ((name :prefix :type keyword)
+   (code :prefix :type (vector byte))
+   (type :prefix :type stack-effect-type)))
+
+(def/class numeric-instr (instr))
+
+(def/class func ()
+  (type :prefix :type typeidx)
+  (locals :type (vector valtype))
+  (body :prefix :type expr))
+
+;;; MODULES
+
+(def/class module ()
+  (types funcs tables mems globals elems datas imports exports
+         :type vector :initform (vector))
+  (start :type (or null t)            ; TODO: what is this value type?
+         :initform nil))
+
+