some rudimentary list operations

stdlib/list.go

@@ -18,6 +18,7 @@
 package stdlib
 
 import (
+    "fmt"
     "gitlab.com/whom/shs/ast"
     "gitlab.com/whom/shs/log"
 )
@@ -28,6 +29,7 @@ import (
  * in event a not-list is passed in, returns the arg.
  */
 func Expand(input *ast.Token, vars ast.VarTable, funcs ast.FuncTable) *ast.Token {
+    input = input.Eval(funcs, vars, false)
     if input.Tag != ast.LIST {
         log.Log(log.INFO, "expand called on not a list", "expand")
         return input
@@ -42,6 +44,7 @@ func Expand(input *ast.Token, vars ast.VarTable, funcs ast.FuncTable) *ast.Token
  * if no args are a list, a list is made from all args
  */
 func L_append(input *ast.Token, vars ast.VarTable, funcs ast.FuncTable) *ast.Token {
+    input = input.Eval(funcs, vars, false)
     src := input
 
     if input.Tag != ast.LIST {
@@ -68,3 +71,76 @@ func L_append(input *ast.Token, vars ast.VarTable, funcs ast.FuncTable) *ast.Tok
 
     return src
 }
+
+/* Len
+ * Returns length of list as a number
+ * Returns nil if not a list
+ *
+ * Example: () -> 0
+ * Example: (1 2 3) -> 3
+ */
+func Len(input *ast.Token, vars ast.VarTable, funcs ast.FuncTable) *ast.Token {
+    input = input.Eval(funcs, vars, false)
+    if input.Tag != ast.LIST {
+        log.Log(log.ERR,
+            "non-list as parameter to head",
+            "head")
+        return nil
+    }
+
+    length := 0
+    for iter := input.Expand(); iter != nil; iter = iter.Next {
+        length += 1
+    }
+
+    ret := &ast.Token{Tag: ast.NUMBER}
+    ret.Set(fmt.Sprintf("%d", length))
+    return ret
+}
+
+/* Head
+ * Returns first element in the list
+ * Returns nil if input is not a list or if list is empty
+ *
+ * Example: (head (2 3 4)) -> 2
+ */
+func Head(input *ast.Token, vars ast.VarTable, funcs ast.FuncTable) *ast.Token {
+    input = input.Eval(funcs, vars, false)
+    if input.Tag != ast.LIST {
+        log.Log(log.ERR,
+            "non-list as parameter to head",
+            "head")
+        return nil
+    }
+
+    li := input.Expand().Copy()
+    if li != nil {
+        li.Next = nil
+    }
+
+    return li
+}
+
+/* Tail
+ * Returns last element in a list
+ * Returns nil if not a list
+ *
+ * Example: (tail (2 3 4)) -> 4
+ */
+func Tail(input *ast.Token, vars ast.VarTable, funcs ast.FuncTable) *ast.Token {
+    input = input.Eval(funcs, vars, false)
+    if input.Tag != ast.LIST {
+        log.Log(log.ERR,
+            "non-list as parameter to head",
+            "head")
+        return nil
+    }
+
+
+    iter := input.Expand()
+    for iter != nil && iter.Next != nil {
+        iter = iter.Next
+    }
+
+    return iter.Copy()
+}