1 files changed, 55 insertions, 0 deletions
diff --git a/interp/interpreter.go b/interp/interpreter.go
new file mode 100644
index 0000000..8d372c3
--- /dev/null
+++ b/interp/interpreter.go
@@ -0,0 +1,55 @@
+// Package interp implements an interpreter.
+package interp
+
+import (
+	"reflect"
+
+	"github.com/mvertes/parscan/comp"
+	"github.com/mvertes/parscan/lang"
+	"github.com/mvertes/parscan/vm"
+)
+
+const debug = true
+
+// Interp represents the state of an interpreter.
+type Interp struct {
+	*comp.Compiler
+	*vm.Machine
+}
+
+// NewInterpreter returns a new interpreter.
+func NewInterpreter(s *lang.Spec) *Interp {
+	return &Interp{comp.NewCompiler(s), &vm.Machine{}}
+}
+
+// Eval evaluates code string and return the last produced value if any, or an error.
+func (i *Interp) Eval(src string) (res reflect.Value, err error) {
+	codeOffset := len(i.Code)
+	dataOffset := 0
+	if codeOffset > 0 {
+		// All data must be copied to the VM the first time only (re-entrance).
+		dataOffset = len(i.Data)
+	}
+	i.PopExit() // Remove last exit from previous run (re-entrance).
+
+	t, err := i.Parse(src)
+	if err != nil {
+		return res, err
+	}
+	if err = i.Generate(t); err != nil {
+		return res, err
+	}
+	i.Push(i.Data[dataOffset:]...)
+	i.PushCode(i.Code[codeOffset:]...)
+	if s, ok := i.Symbols["main"]; ok {
+		i.PushCode(vm.Instruction{Op: vm.Calli, Arg: []int{int(i.Data[s.Index].Int())}})
+	}
+	i.PushCode(vm.Instruction{Op: vm.Exit})
+	i.SetIP(max(codeOffset, i.Entry))
+	if debug {
+		i.PrintData()
+		i.PrintCode()
+	}
+	err = i.Run()
+	return i.Top().Value, err
+}