much improved type inferencing

src/LambdaBlock.tsx

@@ -1,13 +1,14 @@
 import { useContext, useEffect, useRef } from "react";
 
-import { growEnv } from "dope2";
+import { eqType, getSymbol, reduceUnification, trie } from "dope2";
 
 import { ExprBlock, type ExprBlockState, type State2Props } from "./ExprBlock";
 import { EnvContext } from "./EnvContext";
-import { getUnusedTypeVar } from "./eval";
+import { evalEditorBlock, makeInnerEnv, makeTypeVar } from "./eval";
 import { autoInputWidth } from "./util/dom_trickery";
 
 import "./LambdaBlock.css";
+import { Type } from "./Type";
 
 export interface LambdaBlockState {
   kind: "lambda";
@@ -47,11 +48,20 @@ export function LambdaBlock({state, setState, suggestionPriority}: LambdaBlockPr
 
   useEffect(() => autoInputWidth(nameRef, state.paramName, 60), [nameRef, state.paramName]);
 
-  const innerEnv = growEnv(env)(state.paramName)({
-    kind: "unknown",
-    i: undefined,
-    t: getUnusedTypeVar(env),
-  });
+  const [paramType, staticInnerEnv] = makeTypeVar(env, state.paramName);
+
+  const exprResolved = evalEditorBlock(state.expr, staticInnerEnv);
+
+  const inferredParamType = reduceUnification(exprResolved.unification).get(getSymbol(paramType)) || paramType;
+
+  const betterInnerEnv = eqType(paramType)(inferredParamType)
+    ? staticInnerEnv
+    : makeInnerEnv(env, state.paramName, {
+      kind: "unknown",
+      t: inferredParamType,
+      unification: new Map(), // <- is this correct?
+    })
+
   
   return <span className="lambdaBlock">
     <span className="keyword">&#955;</span>
@@ -66,11 +76,14 @@ export function LambdaBlock({state, setState, suggestionPriority}: LambdaBlockPr
           onChange={e => setParamName(e.target.value)}
           />
     </span>
+    <div className="typeSignature">
+        &nbsp;::&nbsp;<Type type={inferredParamType} />
+        </div>
     &nbsp;
     <span className="keyword">:</span>
     &nbsp;
     <div className="lambdaInner">
-      <EnvContext value={innerEnv}>
+      <EnvContext value={betterInnerEnv}>
         <ExprBlock
           state={state.expr}
           setState={setExpr}