add rudimentary control flow

stdlib/stdlib.go

@@ -26,7 +26,28 @@ import (
 func GenFuncTable() ast.FuncTable {
     var stdlib ast.FuncTable
     stdlib = &map[string]*ast.Function{
-        "...": &ast.Function{
+      "if": &ast.Function{
+            Function: shs_if,
+            Name:       "if",
+            TimesCalled:   0,
+            Args:          3,
+        },
+
+      "while": &ast.Function{
+            Function: shs_while,
+            Name:       "while",
+            TimesCalled:      0,
+            Args:            -1,
+        },
+
+      "eval": &ast.Function{
+            Function:   eval,
+            Name:     "eval",
+            TimesCalled:   0,
+            Args:         -1,
+        },
+
+       "...": &ast.Function{
             Function: expand,
             Name:      "...",
             TimesCalled:   0,
@@ -242,3 +263,7 @@ func sh_info(in *ast.Token, vt ast.VarTable, ft ast.FuncTable) *ast.Token {
 
     return nil
 }
+
+func eval(in *ast.Token, vt ast.VarTable, ft ast.VarTable) *ast.Token {
+    return in.Eval(ft, vt, false)
+}