From 15e294085c1f6a5873cde6d0ec028a959f54c82a Mon Sep 17 00:00:00 2001
From: Aidan <aidan@aidanis.online>
Date: Fri, 24 Jul 2020 19:58:09 -0700
Subject: [PATCH] some rudimentary list operations

---
 stdlib/list.go   | 76 ++++++++++++++++++++++++++++++++++++++++++++++++
 stdlib/stdlib.go | 22 ++++++++++++++
 2 files changed, 98 insertions(+)

diff --git a/stdlib/list.go b/stdlib/list.go
index 748414b..863718e 100644
--- a/stdlib/list.go
+++ b/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()
+}
diff --git a/stdlib/stdlib.go b/stdlib/stdlib.go
index 292b7da..2479249 100644
--- a/stdlib/stdlib.go
+++ b/stdlib/stdlib.go
@@ -59,6 +59,28 @@ func GenFuncTable() ast.FuncTable {
             Args:             3,
         },
 
+        "len": &ast.Function{
+            Function:      Len,
+            Name:        "len",
+            TimesCalled:     0,
+            Args:            1,
+        },
+
+        "head": &ast.Function{
+            Function:     Head,
+            Name:       "head",
+            TimesCalled:     0,
+            Args:            1,
+        },
+
+        "tail": &ast.Function{
+            Function:   Tail,
+            Name:     "tail",
+            TimesCalled:   0,
+            Args:          1,
+        },
+
+
         "export": &ast.Function{
             Function: Export,
             Name:   "export",