added progn form

Readme.md

@@ -43,10 +43,11 @@ Use the `func` function from the stdlib:
 In this case, `(form_to_be_evaluated)` will not be evaluated until the function is called.
 
 ### Control flow
-See `stdlib/control_flow.go`. We have if and while forms:
+See `stdlib/control_flow.go`. We have if, while, and progn forms:
 `(if (cond) (then) (else))`
 `(when (cond) (form1)....... (formN))`
-
+`(progn (form1)..... (formN))`
+If and While should be self explanatory. For those new to LISP, the rough idea of progn is to evaluate a sequence of N forms and return the result of the final one.
 We also have functioning implementations of map and reduce in the stdlib (incomplete)
 
 ## Comments

stdlib/control_flow.go

@@ -22,6 +22,17 @@ import (
     "gitlab.com/whom/shs/log"
 )
 
+/* eval N forms. return the last one
+ */
+func shs_progn(in *ast.Token, vt ast.VarTable, ft ast.FuncTable) *ast.Token {
+    var res *ast.Token
+    for iter := in; iter != nil; iter = iter.Next {
+        res = iter.Eval(ft, vt, false)
+    }
+
+    return res
+}
+
 /* return one evaluated form or another based on the boolean statement
  */
 func shs_if(in *ast.Token, vt ast.VarTable, ft ast.FuncTable) *ast.Token {

stdlib/stdlib.go

@@ -42,6 +42,13 @@ func GenFuncTable() ast.FuncTable {
             Args:            -1,
         },
 
+        "progn": &ast.Function{
+            Function:  shs_progn,
+            Name:    "shs_progn",
+            TimesCalled:       0,
+            Args:             -1,
+        },
+
         "eval": &ast.Function{
             Function:   eval,
             Name:     "eval",