Phase 8: Tree-walking interpreter for in-memory REPL eval (~0.02ms vs 1133ms compiled). 66 eval tests.

src/repl.nim

@@ -1,6 +1,6 @@
 # AI-First REPL for Clojure/Nim
-import os, osproc, strutils, json, times, net
-import reader, emitter, types, macros
+import os, osproc, strutils, sequtils, json, times, net
+import reader, emitter, types, macros, eval
 
 type
   ReplMode* = enum
@@ -13,6 +13,7 @@ type
     tempDir*: string
     sessionId*: string
     libPath*: string
+    evalEnv*: Env
 
 proc getLibPath(): string =
   let appDir = getAppDir()
@@ -33,6 +34,7 @@ proc initReplState*(mode: ReplMode): ReplState =
   createDir(result.tempDir)
   result.sessionId = $getCurrentProcessId() & "_" & $epochTime().int
   result.libPath = getLibPath()
+  result.evalEnv = newTopLevelEnv()
 
 proc cleanup*(state: ReplState) =
   try:
@@ -40,6 +42,32 @@ proc cleanup*(state: ReplState) =
   except:
     discard
 
+proc cljReprLocal(v: CljVal): string =
+  if v.isNil: return "nil"
+  case v.kind
+  of ckNil: result = "nil"
+  of ckBool:
+    if v.boolVal: result = "true"
+    else: result = "false"
+  of ckInt: result = $v.intVal
+  of ckFloat: result = $v.floatVal
+  of ckString: result = v.strVal
+  of ckKeyword: result = ":" & v.kwName
+  of ckSymbol: result = v.symName
+  of ckList:
+    var parts: seq[string] = @[]
+    for item in v.items: parts.add(cljReprLocal(item))
+    result = "(" & parts.join(" ") & ")"
+  of ckVector:
+    var parts: seq[string] = @[]
+    for item in v.items: parts.add(cljReprLocal(item))
+    result = "[" & parts.join(" ") & "]"
+  of ckMap:
+    var parts: seq[string] = @[]
+    for i in 0..<v.mapKeys.len:
+      parts.add(cljReprLocal(v.mapKeys[i]) & " " & cljReprLocal(v.mapVals[i]))
+    result = "{" & parts.join(", ") & "}"
+
 proc buildProgram(state: ReplState, form: CljVal, isDef: bool): string =
   var allForms = state.defs
   if isDef:
@@ -114,6 +142,51 @@ proc evalForm*(state: var ReplState, formStr: string): JsonNode =
               parsed.items[0].kind == ckSymbol and
               parsed.items[0].symName in ["def", "defn"]
 
+  # Try in-memory evaluation first (fast path)
+  let evalResult = evalAst(parsed, state.evalEnv)
+  if evalResult.ok:
+    let elapsed = (epochTime() - startTime) * 1000
+
+    if evalResult.isDef:
+      state.defs.add(parsed)
+      return %*{
+        "status": "ok",
+        "result": {
+          "type": "var",
+          "name": evalResult.defName,
+          "ns": state.ns,
+          "printed": "#\"" & state.ns & "/" & evalResult.defName & "\""
+        },
+        "meta": {
+          "ns": state.ns,
+          "ms": elapsed,
+          "form": formStr
+        }
+      }
+
+    var printed: string
+    if evalResult.value.kind == ckNil:
+      printed = "nil"
+    elif evalResult.value.kind == ckString:
+      printed = evalResult.value.strVal
+    else:
+      printed = cljReprLocal(evalResult.value)
+
+    return %*{
+      "status": "ok",
+      "result": {
+        "type": "interpreted",
+        "value": printed,
+        "printed": printed
+      },
+      "meta": {
+        "ns": state.ns,
+        "ms": elapsed,
+        "form": formStr
+      }
+    }
+
+  # Fall back to compilation (slow path)
   let nimCode = buildProgram(state, parsed, isDef)
   let (ok, output, error) = compileAndRun(state, nimCode)
 
@@ -154,7 +227,7 @@ proc evalForm*(state: var ReplState, formStr: string): JsonNode =
   return %*{
     "status": "ok",
     "result": {
-      "type": "unknown",
+      "type": "compiled",
       "value": output,
       "printed": output
     },