fix: Separate typed instance for each PocomathInstance (#15)

Also starts each PocomathInstance with no types at all, and uses the new
  situation to eliminate the need for a Complex "base case".

  Resolves #14.
  Resolves #13.

Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: #15

src/core/PocomathInstance.mjs

@@ -0,0 +1,178 @@
+/* Core of pocomath: create an instance */
+import typed from 'typed-function'
+
+export default class PocomathInstance {
+   constructor(name) {
+      this.name = name
+      this._imps = {}
+      this._affects = {}
+      this._typed = typed.create()
+      this._typed.clear()
+      // Convenient hack for now, would remove when a real string type is added:
+      this._typed.addTypes([{name: 'string', test: s => typeof s === 'string'}])
+   }
+    
+   /**
+    * (Partially) define one or more operations of the instance:
+    *
+    * @param {Object<string, Object<Signature, [string[], function]>>} ops
+    *    The only parameter ops gives the semantics of the operations to install.
+    *    The keys are operation names. The value for a key is an object
+    *    mapping (typed-function) signature strings to pairs of dependency
+    *    lists and implementation functions.
+    *
+    *    A dependency list is a list of strings. Each string can either be the
+    *    name of a function that the corresponding implementation has to call,
+    *    or a specification of a particular signature of a function that it has
+    *    to call, in the form 'FN(SIGNATURE)'. Note the function name can be
+    *    the special value 'self' to indicate a recursive call to the given
+    *    operation (either with or without a particular signature.
+    *
+    *    There are two cases for the implementation function. If the dependency
+    *    list is empty, it should be a function taking the arguments specified
+    *    by the signature and returning the value. Otherwise, it should be
+    *    a function taking an object with the dependency lists as keys and the
+    *    requested functions as values, to a function taking the arguments
+    *    specified by the signature and returning the value.
+    *
+    *    Note that the "operation" named `Types` is special: it gives
+    *    types that must be installed in the instance. In this case, the keys
+    *    are type names, and the values are objects with a property 'test'
+    *    giving the predicate for the type, and properties for each type that can
+    *    be converted **to** this type, giving the corresponding conversion
+    *    function.
+    */
+   install(ops) {
+      for (const key in ops) this._installOp(key, ops[key])
+   }
+
+   /* Used internally by install, see the documentation there */
+   _installOp(name, implementations) {
+      // new implementations, so set the op up to lazily recreate itself
+      this._invalidate(name)
+      const opImps = this._imps[name]
+      for (const signature in implementations) {
+         if (signature in opImps) {
+            if (implementations[signature] === opImps[signature]) continue
+            throw new SyntaxError(
+               `Conflicting definitions of ${signature} for ${name}`)
+         } else {
+            opImps[signature] = implementations[signature]
+            for (const dep of implementations[signature][0] || []) {
+               const depname = dep.split('(', 1)[0]
+               if (depname === 'self') continue
+               if (!(depname in this._affects)) {
+                  this._affects[depname] = new Set()
+               }
+               this._affects[depname].add(name)
+            }
+         }
+      }
+   }
+
+   /**
+    * Reset an operation to require creation of typed-function,
+    * and if it has no implementations so far, set them up.
+    */
+   _invalidate(name) {
+      const self = this
+      this[name] = function () {
+         return self._bundle(name).apply(self, arguments)
+      }
+      if (!(name in this._imps)) {
+         this._imps[name] = {}
+      }
+      if (name in this._affects) {
+         for (const ancestor of this._affects[name]) {
+            this._invalidate(ancestor)
+         }
+      }
+   }
+
+   /**
+    * Create a typed-function from the signatures for the given name and
+    * assign it to the property with that name, returning it as well
+    */
+   _bundle(name) {
+      const imps = this._imps[name]
+      if (!imps || Object.keys(imps).length === 0) {
+         throw new SyntaxError(`No implementations for ${name}`)
+      }
+      this._ensureTypes()
+      const tf_imps = {}
+      for (const signature in imps) {
+         const [deps, imp] = imps[signature]
+         if (deps.length === 0) {
+            tf_imps[signature] = imp
+         } else {
+            const refs = {}
+            let self_referential = false
+            for (const dep of deps) {
+               // TODO: handle signature-specific dependencies
+               if (dep.includes('(')) {
+                  throw new Error('signature specific reference unimplemented')
+               }
+               if (dep === 'self') {
+                  self_referential = true
+               } else {
+                  refs[dep] = this._ensureBundle(dep) // assume acyclic for now
+               }
+            }
+            if (self_referential) {
+               tf_imps[signature] = this._typed.referToSelf(self => {
+                  refs.self = self
+                  return imp(refs)
+               })
+            } else {
+               tf_imps[signature] = imp(refs)
+            }
+         }
+      }
+      const tf = this._typed(name, tf_imps)
+      this[name] = tf
+      return tf
+   }
+
+   /**
+    * Ensure that the generated typed function is assigned to the given
+    * name and return it
+    */
+   _ensureBundle(name) {
+      const maybe = this[name]
+      if (this._typed.isTypedFunction(maybe)) return maybe
+      return this._bundle(name)
+   }
+
+   /**
+    * Ensure that all of the requested types and conversions are actually
+    * in the typed-function universe:
+    */
+   _ensureTypes() {
+      const newTypes = []
+      const newTypeSet = new Set()
+      const knownTypeSet = new Set()
+      const conversions = []
+      const typeSpec = this._imps.Types
+      for (const name in this._imps.Types) {
+         knownTypeSet.add(name)
+         for (const from in typeSpec[name]) {
+            if (from === 'test') continue;
+            conversions.push(
+               {from, to: name, convert: typeSpec[name][from]})
+         }
+         try { // Hack: work around typed-function #154
+            this._typed._findType(name)
+         } catch {
+            newTypeSet.add(name)
+            newTypes.push({name, test: typeSpec[name].test})
+         }
+      }
+      this._typed.addTypes(newTypes)
+      const newConversions = conversions.filter(
+         item => (newTypeSet.has(item.from) || newTypeSet.has(item.to)) &&
+            knownTypeSet.has(item.from) && knownTypeSet.has(item.to)
+      )
+      this._typed.addConversions(newConversions)
+   }
+
+}