refactored ast tables, added eval method

ast/eval.go

@@ -0,0 +1,70 @@
+/*   SHS: Syntactically Homogeneous Shell
+ *   Copyright (C) 2019  Aidan Hahn
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package ast
+
+type Tree *Token
+
+func (Tree t) Eval(FuncTable funcs, VarTable vars) Tree {
+    if t == nil {
+        return
+    }
+
+    var iter *Token
+    eligibleForSystemCall := true
+
+    reduce := func(Tree t_) Tree {
+        if t_.Next != nil {
+            t_.Next = reduce(t_.Next)
+        }
+
+        switch (t_.Tag) {
+        case SYMBOL:
+            maybeToken := GetVar(t_.Inner, vars)
+            if maybeToken != nil {
+                tok := maybeToken.Eval(funcs, vars)
+                if tok == LIST {
+                    eligibleForSystemCall = false
+                }
+            }
+
+        case LIST:
+            eligibleForSystemCall = false
+            t.Inner = Eval(t_.Inner)
+        }
+
+        return t_
+    }
+
+    ret := reduce(t)
+    if ret.Tag == SYMBOL {
+        f := funcs.GetFunction(ret.Inner)
+        if f == nil {
+            if !eligibleForSystemCall {
+                // TODO: log error
+                return nil
+            }
+
+            // hook into stdlib exec
+            return
+        }
+
+        return (*f).CallFunction(ret.Next)
+    }
+
+    return ret
+}