diff --git a/compiler/genpc/genpc.go b/compiler/genpc/genpc.go
index 49efb61..5b67627 100644
--- a/compiler/genpc/genpc.go
+++ b/compiler/genpc/genpc.go
@@ -291,17 +291,42 @@ func (g *generator) emitFor(s *ast.ForStmt) {
 	if !ok {
 		return
 	}
-	// Init
+	// Init: var := start
 	g.emitExpr(s.Start)
 	g.emit(hbrt.PcOpPopLocal)
 	g.emitU16(uint16(idx))
 
+	// Detect step direction statically (matches gengo's emitFor):
+	//   * no Step      → +1, ascending
+	//   * literal -N   → descending
+	//   * unary MINUS  → descending
+	// Anything else (variable, expression) defaults to ascending.
+	// Without this we always emitted `var <= to`, which made `FOR
+	// 5 TO 1 STEP -1` exit on the first iteration; and we always
+	// stepped by hardcoded +1, which made `FOR i := 1 TO 10 STEP
+	// 2` summed 1+2+...+10 (55) instead of 1+3+5+7+9 (25).
+	negStep := false
+	if s.Step != nil {
+		if lit, ok := s.Step.(*ast.LiteralExpr); ok {
+			if lit.Kind == token.INT && len(lit.Value) > 0 && lit.Value[0] == '-' {
+				negStep = true
+			}
+		}
+		if un, ok := s.Step.(*ast.UnaryExpr); ok && un.Op == token.MINUS {
+			negStep = true
+		}
+	}
+
 	loopStart := g.pc()
-	// Check: var <= to
+	// Comparison: ascending → var <= to; descending → var >= to.
 	g.emit(hbrt.PcOpPushLocal)
 	g.emitU16(uint16(idx))
 	g.emitExpr(s.To)
-	g.emit(hbrt.PcOpLessEq)
+	if negStep {
+		g.emit(hbrt.PcOpGreaterEq)
+	} else {
+		g.emit(hbrt.PcOpLessEq)
+	}
 	jumpOut := g.emitJumpPlaceholder(hbrt.PcOpJumpFalse)
 
 	// Body
@@ -309,30 +334,22 @@ func (g *generator) emitFor(s *ast.ForStmt) {
 		g.emitStmt(stmt)
 	}
 
-	// Step
+	// Increment: var := var + step (re-evaluating step per iter is
+	// fine; constant-folding can hoist it later). Push var, push
+	// step, add, store back.
+	g.emit(hbrt.PcOpPushLocal)
+	g.emitU16(uint16(idx))
 	if s.Step != nil {
 		g.emitExpr(s.Step)
 	} else {
 		g.emit(hbrt.PcOpPushInt)
 		g.emitI64(1)
 	}
-	g.emit(hbrt.PcOpPushLocal)
+	g.emit(hbrt.PcOpPlus)
+	g.emit(hbrt.PcOpPopLocal)
 	g.emitU16(uint16(idx))
-	g.emit(hbrt.PcOpPlus) // swap order: step + local
-	// Actually need: local + step
-	// Fix: push local first, then step, then plus
-	// Let me redo:
-	// Undo the above and redo properly
-	g.code = g.code[:len(g.code)-1] // remove PcOpPlus
-	// Remove the PushLocal
-	g.code = g.code[:len(g.code)-3]
-	// Remove the step expr or PushInt
-	// This is getting complicated. Let me use LocalAddInt for simple step.
-	g.emit(hbrt.PcOpLocalAddInt)
-	g.emitU16(uint16(idx))
-	g.emitI32(1) // default step = 1
 
-	// Jump back
+	// Jump back to comparison
 	g.emit(hbrt.PcOpJump)
 	g.emitI32(int32(loopStart - g.pc() - 4))
 
@@ -557,6 +574,28 @@ func (g *generator) emitCallStmt(e *ast.CallExpr) {
 }
 
 func (g *generator) emitAssign(a *ast.AssignExpr) {
+	// Compound operators (+=, -=, *=, /=, %=, ^=) need to fold the
+	// existing left-hand value with the right. Without this they got
+	// emitted as plain `:=`, dropping the accumulator: `n += i`
+	// behaved as `n := i`. So the FOR loop reduce idiom (e.g.
+	// `n := 0 ; FOR i := 1 TO 10 ; n += i ; NEXT`) returned only
+	// the LAST iteration's increment.
+	if a.Op != token.ASSIGN {
+		op, ok := compoundBinOp(a.Op)
+		if ok {
+			if ident, isIdent := a.Left.(*ast.IdentExpr); isIdent {
+				if idx, found := g.locals[ident.Name]; found {
+					g.emit(hbrt.PcOpPushLocal)
+					g.emitU16(uint16(idx))
+					g.emitExpr(a.Right)
+					g.emit(op)
+					g.emit(hbrt.PcOpPopLocal)
+					g.emitU16(uint16(idx))
+					return
+				}
+			}
+		}
+	}
 	if ident, ok := a.Left.(*ast.IdentExpr); ok {
 		if idx, found := g.locals[ident.Name]; found {
 			g.emitExpr(a.Right)
@@ -577,6 +616,27 @@ func (g *generator) emitAssign(a *ast.AssignExpr) {
 	g.emit(hbrt.PcOpPop)
 }
 
+// compoundBinOp maps an `<op>=` token to the binary opcode it
+// produces against the left-hand value. Returns false for ASSIGN
+// (the caller should take the plain-store path).
+func compoundBinOp(k token.Kind) (byte, bool) {
+	switch k {
+	case token.PLUSEQ:
+		return hbrt.PcOpPlus, true
+	case token.MINUSEQ:
+		return hbrt.PcOpMinus, true
+	case token.STAREQ:
+		return hbrt.PcOpMult, true
+	case token.SLASHEQ:
+		return hbrt.PcOpDivide, true
+	case token.PERCENTEQ:
+		return hbrt.PcOpMod, true
+	case token.POWEREQ:
+		return hbrt.PcOpPower, true
+	}
+	return 0, false
+}
+
 func parseInt64(s string) int64 {
 	var v int64
 	for _, c := range s {
diff --git a/hbrt/frbmem.go b/hbrt/frbmem.go
index 554efcc..ebd3bf9 100644
--- a/hbrt/frbmem.go
+++ b/hbrt/frbmem.go
@@ -24,14 +24,34 @@ import (
 )
 
 // FrbCompileSource compiles PRG source code to an FRB module in memory.
-// If Go compiler is available, uses native plugin mode.
-// If not, falls back to pcode interpreter mode (--pcode).
+// Strategy:
+//   1. If Go isn't installed, go straight to pcode mode.
+//   2. Try the native Go-plugin path first (faster, native speed).
+//   3. If the plugin build fails, OR if loading the resulting plugin
+//      fails (the most common failure: "plugin was built with a
+//      different version of package runtime", which fires whenever
+//      the host binary and the plugin weren't compiled byte-for-byte
+//      against the same Go runtime — happens routinely after `go
+//      build` rebuilds), fall back to pcode mode. Pcode is a few x
+//      slower but always works.
 func FrbCompileSource(vm *VM, prgSource string, fiveExe string) (*FrbModule, error) {
-	// Check if Go is available
 	if !isGoAvailable() {
 		return frbCompilePcode(vm, prgSource, fiveExe)
 	}
 
+	mod, err := frbCompilePlugin(vm, prgSource, fiveExe)
+	if err == nil {
+		return mod, nil
+	}
+	// Plugin path failed — try pcode. Don't surface the plugin
+	// error: pcode either works (return its module) or doesn't
+	// (return its error).
+	return frbCompilePcode(vm, prgSource, fiveExe)
+}
+
+// frbCompilePlugin is the original native-plugin path, factored out
+// of FrbCompileSource so the latter can pick a fallback on failure.
+func frbCompilePlugin(vm *VM, prgSource string, fiveExe string) (*FrbModule, error) {
 	tmpDir, err := os.MkdirTemp("", "frb-mem-*")
 	if err != nil {
 		return nil, err
diff --git a/hbrt/thread.go b/hbrt/thread.go
index 386e8d5..3015160 100644
--- a/hbrt/thread.go
+++ b/hbrt/thread.go
@@ -219,6 +219,30 @@ func (t *Thread) Pop()       { t.pop() }
 func (t *Thread) Pop2() Value { return t.pop() } // pop and return
 func (t *Thread) Dup()       { t.push(t.peek()) }
 
+// SP returns the current data-stack depth. Paired with SetSP for
+// callers that need to clamp the stack across an inner function
+// dispatch — used by FrbDo to neutralise pcode-body stack leaks.
+func (t *Thread) SP() int { return t.sp }
+
+// SetSP forcibly resets the data-stack depth. Truncates if newSP < sp;
+// extends with NIL if newSP > sp (defensive — should never grow here
+// in practice). Bounds-checked against the underlying slice so a
+// negative or out-of-range value can't corrupt the runtime.
+func (t *Thread) SetSP(newSP int) {
+	if newSP < 0 {
+		newSP = 0
+	}
+	if newSP > len(t.stack) {
+		newSP = len(t.stack)
+	}
+	// Clear any slots being abandoned so stale values can't surface
+	// later through Dup/peek paths.
+	for i := newSP; i < t.sp; i++ {
+		t.stack[i] = cachedNil
+	}
+	t.sp = newSP
+}
+
 // --- Frame management ---
 // Harbour: hb_xvmFrame(params, locals)
 // Called at the start of every function.
diff --git a/hbrtl/frb.go b/hbrtl/frb.go
index 27d1d55..181c298 100644
--- a/hbrtl/frb.go
+++ b/hbrtl/frb.go
@@ -14,6 +14,9 @@
 package hbrtl
 
 import (
+	"five/compiler/genpc"
+	"five/compiler/parser"
+	"five/compiler/pp"
 	"five/hbrt"
 	"fmt"
 	"os"
@@ -22,6 +25,65 @@ import (
 	"strings"
 )
 
+// frbCompileInProc compiles PRG source to a pcode FrbModule entirely
+// in-process — no external `five` binary needed. Used by FrbCompile/
+// FrbExec when the host can't shell out (running from a directory
+// where `five` isn't on PATH and isn't next to the binary). Avoids
+// the plugin-runtime-mismatch failure mode of native FRB plugins
+// AND removes the "find the five exe" fragility entirely.
+func frbCompileInProc(vm *hbrt.VM, prgSource string) (*hbrt.FrbModule, error) {
+	prep := pp.New()
+	processed, errs := prep.Process("dynamic.prg", prgSource)
+	if len(errs) > 0 {
+		return nil, fmt.Errorf("preprocess: %s", strings.Join(errs, "; "))
+	}
+	file, perrs := parser.Parse("dynamic.prg", processed)
+	if len(perrs) > 0 {
+		msgs := make([]string, 0, len(perrs))
+		for _, e := range perrs {
+			msgs = append(msgs, e.Error())
+		}
+		return nil, fmt.Errorf("parse: %s", strings.Join(msgs, "; "))
+	}
+	pcMod := genpc.Generate(file)
+
+	// Build a FrbModule from the pcode functions. Mirrors what
+	// hbrt/frb.go's frbLoadPcode does, but without the disk hop.
+	frbMod := &hbrt.FrbModule{
+		Name:      "dynamic",
+		LocalSyms: make(map[string]*hbrt.Symbol),
+		OldSyms:   make(map[string]*hbrt.Symbol),
+		BindMode:  hbrt.FrbBindDefault,
+		VM:        vm,
+	}
+	for name, fn := range pcMod.Funcs {
+		pcFn := fn
+		pcModRef := pcMod
+		goFunc := func(t *hbrt.Thread) {
+			hbrt.ExecPcode(t, pcFn, pcModRef)
+		}
+		frbMod.LocalSyms[name] = &hbrt.Symbol{
+			Name:  name,
+			Scope: hbrt.FsPublic | hbrt.FsLocal,
+			Func:  goFunc,
+		}
+	}
+	// Register non-Main symbols globally (Main stays module-local).
+	for name, sym := range frbMod.LocalSyms {
+		if name == "MAIN" {
+			continue
+		}
+		old := vm.FindSymbol(name)
+		if old != nil {
+			frbMod.OldSyms[name] = old
+			continue
+		}
+		vm.RegisterSymbol(sym)
+		frbMod.Registered = append(frbMod.Registered, name)
+	}
+	return frbMod, nil
+}
+
 // findFiveExe locates the 'five' compiler binary
 func findFiveExe() string {
 	// 1. Check same directory as running executable
@@ -86,6 +148,16 @@ func FrbDoFunc(t *hbrt.Thread) {
 		return
 	}
 
+	// Snapshot SP *before* pushing args. After the inner call,
+	// Frame()/PcOpRetValue should have left SP back at this baseline,
+	// but pcode-mode bodies can occasionally leak intermediate stack
+	// values (e.g. FOR-loop control vestiges). Reseating SP to the
+	// snapshot before reading retVal stops those leaks from polluting
+	// the caller's argument frame — which is what made
+	// `? "label", FrbDo(...), "tail"` show "1" or "2" in place of the
+	// label string when the inner function had a loop.
+	savedSP := t.SP()
+
 	// Push args for the function
 	for i := 3; i <= nParams; i++ {
 		t.PushValue(t.Local(i))
@@ -93,6 +165,7 @@ func FrbDoFunc(t *hbrt.Thread) {
 	t.PendingParams2(nParams - 2)
 	fn(t)
 
+	t.SetSP(savedSP)
 	t.PushValue(t.GetRetValue())
 	t.RetValue()
 }
@@ -112,14 +185,17 @@ func FrbUnloadFunc(t *hbrt.Thread) {
 }
 
 // FRBCOMPILE(cPrgSource) → pModule
-// Compile PRG source string to FRB module in memory.
+// Compile PRG source string to FRB module in memory. In-process pcode
+// compilation is the default — no external `five` binary or `go`
+// toolchain needed at runtime. The legacy native-plugin path is still
+// reachable via hbrt.FrbCompileSource for callers that want it, but
+// that path is fragile (Go plugins require byte-identical runtime).
 func FrbCompileFunc(t *hbrt.Thread) {
 	t.Frame(1, 0)
 	defer t.EndProc()
 
 	source := t.Local(1).AsString()
-	fiveExe := findFiveExe()
-	mod, err := hbrt.FrbCompileSource(t.VM(), source, fiveExe)
+	mod, err := frbCompileInProc(t.VM(), source)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "FrbCompile error: %v\n", err)
 		t.RetNil()
@@ -136,8 +212,7 @@ func FrbExecFunc(t *hbrt.Thread) {
 	defer t.EndProc()
 
 	source := t.Local(1).AsString()
-	fiveExe := findFiveExe()
-	mod, err := hbrt.FrbCompileSource(t.VM(), source, fiveExe)
+	mod, err := frbCompileInProc(t.VM(), source)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "FrbExec error: %v\n", err)
 		t.RetNil()
@@ -145,18 +220,23 @@ func FrbExecFunc(t *hbrt.Thread) {
 	}
 	defer hbrt.FrbUnload(mod)
 
-	// Find and execute MAIN
-	sym := t.VM().FindSymbol("MAIN")
-	if sym == nil || sym.Func == nil {
+	// Look up MAIN inside the freshly-compiled module first, NOT
+	// via t.VM().FindSymbol — Main is intentionally kept module-local
+	// (frbLoadPcode skips it during VM registration), so a global
+	// lookup would resolve to the *caller's* Main and recurse forever.
+	fn := mod.FindFunc("MAIN")
+	if fn == nil {
 		t.RetNil()
 		return
 	}
 
+	savedSP := t.SP()
 	for i := 2; i <= nParams; i++ {
 		t.PushValue(t.Local(i))
 	}
 	t.PendingParams2(nParams - 1)
-	sym.Func(t)
+	fn(t)
+	t.SetSP(savedSP)
 
 	t.PushValue(t.GetRetValue())
 	t.RetValue()
@@ -177,19 +257,22 @@ func FrbRunFunc(t *hbrt.Thread) {
 	}
 	defer hbrt.FrbUnload(mod)
 
-	// Find MAIN symbol
-	sym := t.VM().FindSymbol("MAIN")
-	if sym == nil || sym.Func == nil {
+	// Same module-local Main lookup as FrbExec — see comment there
+	// for why a t.VM().FindSymbol("MAIN") would recurse into the
+	// outer (caller's) Main.
+	fn := mod.FindFunc("MAIN")
+	if fn == nil {
 		t.RetNil()
 		return
 	}
 
-	// Push args
+	savedSP := t.SP()
 	for i := 2; i <= nParams; i++ {
 		t.PushValue(t.Local(i))
 	}
 	t.PendingParams2(nParams - 1)
-	sym.Func(t)
+	fn(t)
+	t.SetSP(savedSP)
 
 	t.PushValue(t.GetRetValue())
 	t.RetValue()
diff --git a/tests/frb/frb_simple.prg b/tests/frb/frb_simple.prg
new file mode 100644
index 0000000..8367dcf
--- /dev/null
+++ b/tests/frb/frb_simple.prg
@@ -0,0 +1,12 @@
+FUNCTION GiveFive()
+   RETURN 5
+
+FUNCTION AddOne(n)
+   RETURN n + 1
+
+FUNCTION CountTo3()
+   LOCAL i, sum := 0
+   FOR i := 1 TO 3
+      sum := sum + i
+   NEXT
+   RETURN sum
diff --git a/tests/frb/run.sh b/tests/frb/run.sh
new file mode 100755
index 0000000..2507789
--- /dev/null
+++ b/tests/frb/run.sh
@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+#
+# FRB regression runner. Each test exercises a different aspect of
+# Five's runtime compilation / loading pipeline:
+#
+#   frb_simple        — fixture PRG built into a pcode FRB module.
+#   test_frb_simple   — load `frb_simple.frb`, call its functions.
+#   test_frb_pcode_load — load mathlib (multi-function pcode FRB).
+#   test_frb_compile  — FrbCompile / FrbExec — in-memory compile.
+#   test_frb_loop     — FOR loop accumulators (`+=` and `:=`).
+#   test_frb_step     — FOR ... STEP -1 / STEP 2 in pcode mode.
+#
+# Builds frb_simple.frb (and mathlib_pc.frb if needed) into the
+# scratch dir before running the loaders.
+set -e
+
+ROOT="$(cd "$(dirname "$0")/../.." && pwd)"
+FIVE="$ROOT/five"
+[ -x "$FIVE" ] || { echo "five not built — run 'go build -o five ./cmd/five'" >&2; exit 2; }
+
+work="$(mktemp -d)"
+trap 'rm -rf "$work"' EXIT
+
+# Pre-build pcode FRB fixtures the loader tests refer to.
+"$FIVE" frb "$ROOT/tests/frb/frb_simple.prg" -o /tmp/frb_simple.frb --pcode >/dev/null
+"$FIVE" frb "$ROOT/examples/frb_mathlib.prg" -o /tmp/mathlib_pc.frb --pcode >/dev/null
+
+# Test files in the order they should run. test_frb_compile
+# exercises the in-process compiler, which has no external
+# dependencies — runs from any directory.
+TESTS=(
+   test_frb_simple
+   test_frb_pcode_load
+   test_frb_compile
+   test_frb_loop
+   test_frb_step
+)
+
+pass=0
+fail=0
+for name in "${TESTS[@]}"; do
+   src="$ROOT/tests/frb/${name}.prg"
+   bin="$work/${name}"
+   if ! "$FIVE" build "$src" -o "$bin" >/dev/null 2>"$work/${name}.err"; then
+      echo "FAIL build  $name"
+      sed 's/^/   /' "$work/${name}.err"
+      fail=$((fail+1))
+      continue
+   fi
+   if ! out="$("$bin" 2>&1)"; then
+      echo "FAIL run    $name"
+      echo "$out" | sed 's/^/   /'
+      fail=$((fail+1))
+      continue
+   fi
+   if echo "$out" | grep -qE 'FAIL|expect.*got|panic'; then
+      echo "FAIL assert $name"
+      echo "$out" | sed 's/^/   /'
+      fail=$((fail+1))
+      continue
+   fi
+   echo "PASS         $name"
+   pass=$((pass+1))
+done
+
+echo
+echo "================================================================"
+echo "  Results: $pass / $((pass+fail)) passed"
+echo "================================================================"
+[ $fail -eq 0 ]
diff --git a/tests/frb/test_frb_compile.prg b/tests/frb/test_frb_compile.prg
new file mode 100644
index 0000000..6ea880c
--- /dev/null
+++ b/tests/frb/test_frb_compile.prg
@@ -0,0 +1,38 @@
+/* In-memory PRG compilation via FrbCompile / FrbExec. */
+
+FUNCTION Main()
+   LOCAL pStr, cSource
+
+   /* 1. FrbCompile a small lib, call its functions */
+   cSource := ;
+      'FUNCTION Reverse(cStr)' + Chr(10) + ;
+      '   LOCAL i, cResult := ""' + Chr(10) + ;
+      '   FOR i := Len(cStr) TO 1 STEP -1' + Chr(10) + ;
+      '      cResult += SubStr(cStr, i, 1)' + Chr(10) + ;
+      '   NEXT' + Chr(10) + ;
+      '   RETURN cResult' + Chr(10) + ;
+      'FUNCTION Triple(n)' + Chr(10) + ;
+      '   RETURN n * 3' + Chr(10)
+
+   pStr := FrbCompile(cSource)
+   IF pStr == NIL
+      ? "FAIL: FrbCompile returned NIL"
+      RETURN NIL
+   ENDIF
+
+   ? "1. Reverse('Hello') =", FrbDo(pStr, "REVERSE", "Hello"), "(expect olleH)"
+   ? "2. Triple(7)        =", FrbDo(pStr, "TRIPLE", 7),        "(expect 21)"
+   FrbUnload(pStr)
+
+   /* 2. One-shot FrbExec */
+   ? "3. Sum 1..100 via FrbExec:"
+   ? "   ", FrbExec( ;
+      'FUNCTION Main()' + Chr(10) + ;
+      '   LOCAL i, n := 0' + Chr(10) + ;
+      '   FOR i := 1 TO 100' + Chr(10) + ;
+      '      n += i' + Chr(10) + ;
+      '   NEXT' + Chr(10) + ;
+      '   RETURN n' + Chr(10) ), "(expect 5050)"
+
+   ? "DONE"
+   RETURN NIL
diff --git a/tests/frb/test_frb_loop.prg b/tests/frb/test_frb_loop.prg
new file mode 100644
index 0000000..7e9be5b
--- /dev/null
+++ b/tests/frb/test_frb_loop.prg
@@ -0,0 +1,33 @@
+FUNCTION Main()
+   LOCAL r
+
+   /* in-memory compile a simple loop */
+   r := FrbExec( ;
+      'FUNCTION Main()' + Chr(10) + ;
+      '   LOCAL i, n := 0' + Chr(10) + ;
+      '   FOR i := 1 TO 10' + Chr(10) + ;
+      '      n := n + i' + Chr(10) + ;
+      '   NEXT' + Chr(10) + ;
+      '   RETURN n' + Chr(10) )
+   ? "sum 1..10 (using :=) =", r, "(expect 55)"
+
+   r := FrbExec( ;
+      'FUNCTION Main()' + Chr(10) + ;
+      '   LOCAL i, n := 0' + Chr(10) + ;
+      '   FOR i := 1 TO 10' + Chr(10) + ;
+      '      n += i' + Chr(10) + ;
+      '   NEXT' + Chr(10) + ;
+      '   RETURN n' + Chr(10) )
+   ? "sum 1..10 (using +=) =", r, "(expect 55)"
+
+   /* string accumulator */
+   r := FrbExec( ;
+      'FUNCTION Main()' + Chr(10) + ;
+      '   LOCAL i, s := ""' + Chr(10) + ;
+      '   FOR i := 1 TO 5' + Chr(10) + ;
+      '      s := s + Str(i, 1)' + Chr(10) + ;
+      '   NEXT' + Chr(10) + ;
+      '   RETURN s' + Chr(10) )
+   ? "concat 1..5         =", r, '(expect "12345")'
+
+   RETURN NIL
diff --git a/tests/frb/test_frb_pcode_load.prg b/tests/frb/test_frb_pcode_load.prg
new file mode 100644
index 0000000..c186cb0
--- /dev/null
+++ b/tests/frb/test_frb_pcode_load.prg
@@ -0,0 +1,20 @@
+/* Test loading + calling a pcode FRB module. */
+
+FUNCTION Main()
+   LOCAL pMod
+
+   pMod := FrbLoad("/tmp/mathlib_pc.frb")
+   IF pMod == NIL
+      ? "FAIL: FrbLoad returned NIL"
+      RETURN NIL
+   ENDIF
+
+   ? "CircleArea(5.0)  =", FrbDo(pMod, "CIRCLEAREA", 5.0), "(expect 78.539...)"
+   ? "Fibonacci(10)    =", FrbDo(pMod, "FIBONACCI", 10),   "(expect 55)"
+   ? "Fibonacci(20)    =", FrbDo(pMod, "FIBONACCI", 20),   "(expect 6765)"
+   ? "IsPrime(97)      =", FrbDo(pMod, "ISPRIME", 97),     "(expect .T.)"
+   ? "IsPrime(100)     =", FrbDo(pMod, "ISPRIME", 100),    "(expect .F.)"
+
+   FrbUnload(pMod)
+   ? "DONE"
+   RETURN NIL
diff --git a/tests/frb/test_frb_simple.prg b/tests/frb/test_frb_simple.prg
new file mode 100644
index 0000000..c740097
--- /dev/null
+++ b/tests/frb/test_frb_simple.prg
@@ -0,0 +1,9 @@
+FUNCTION Main()
+   LOCAL pMod := FrbLoad("/tmp/frb_simple.frb")
+
+   ? "A:", FrbDo(pMod, "GIVEFIVE"),       "(expect 5)"
+   ? "B:", FrbDo(pMod, "ADDONE", 100),    "(expect 101)"
+   ? "C:", FrbDo(pMod, "COUNTTO3"),       "(expect 6)"
+
+   FrbUnload(pMod)
+   RETURN NIL
diff --git a/tests/frb/test_frb_step.prg b/tests/frb/test_frb_step.prg
new file mode 100644
index 0000000..00bbf71
--- /dev/null
+++ b/tests/frb/test_frb_step.prg
@@ -0,0 +1,24 @@
+FUNCTION Main()
+   LOCAL r
+
+   /* STEP -1 (downward) */
+   r := FrbExec( ;
+      'FUNCTION Main()' + Chr(10) + ;
+      '   LOCAL i, n := 0' + Chr(10) + ;
+      '   FOR i := 5 TO 1 STEP -1' + Chr(10) + ;
+      '      n := n + i' + Chr(10) + ;
+      '   NEXT' + Chr(10) + ;
+      '   RETURN n' + Chr(10) )
+   ? "FOR 5 TO 1 STEP -1 sum =", r, "(expect 15)"
+
+   /* STEP 2 (upward by 2) */
+   r := FrbExec( ;
+      'FUNCTION Main()' + Chr(10) + ;
+      '   LOCAL i, n := 0' + Chr(10) + ;
+      '   FOR i := 1 TO 10 STEP 2' + Chr(10) + ;
+      '      n := n + i' + Chr(10) + ;
+      '   NEXT' + Chr(10) + ;
+      '   RETURN n' + Chr(10) )
+   ? "FOR 1 TO 10 STEP 2 sum =", r, "(expect 25)"
+
+   RETURN NIL