From 2bad76314f90cb871122b8395feddf79c1de843e Mon Sep 17 00:00:00 2001
From: Hans Svensson <hans.svensson@quviq.com>
Date: Mon, 24 Feb 2020 15:34:23 +0100
Subject: [PATCH] More efficient implementations in String.aes

---
 priv/stdlib/String.aes | 63 +++++++++++++++++++++++++-----------------
 1 file changed, 37 insertions(+), 26 deletions(-)

diff --git a/priv/stdlib/String.aes b/priv/stdlib/String.aes
index db5242f..9e9efb2 100644
--- a/priv/stdlib/String.aes
+++ b/priv/stdlib/String.aes
@@ -15,30 +15,41 @@ namespace String =
     (StringInternal.from_list(List.take(i, cs)), StringInternal.from_list(List.drop(i, cs)))
 
   function at(ix : int, s : string) =
-    switch(List.drop(ix - 1, StringInternal.to_list(s)))
+    switch(List.drop(ix, StringInternal.to_list(s)))
       []     => None
       x :: _ => Some(x)
 
-  function tokens(s : string, pat : string) =
-    let pat_len = StringInternal.length(pat)
-    tokens_(StringInternal.to_list(pat), StringInternal.to_list(s), [])
-
   function to_upper(s : string) =
-    StringInternal.from_list([ Char.to_upper(c) | c <- StringInternal.to_list(s) ])
+    StringInternal.from_list(List.map(Char.to_upper, StringInternal.to_list(s)))
 
   function to_lower(s : string) =
-    StringInternal.from_list([ Char.to_lower(c) | c <- StringInternal.to_list(s) ])
+    StringInternal.from_list(List.map(Char.to_lower, StringInternal.to_list(s)))
 
   function contains(str : string, substr : string) : option(int) =
-    let last_ix = StringInternal.length(str) - (StringInternal.length(substr) - 1)
-    contains_(1, last_ix, StringInternal.to_list(str), StringInternal.to_list(substr))
+    if(substr == "") Some(0)
+    else
+      contains_(0, StringInternal.to_list(str), StringInternal.to_list(substr))
 
-  function
-    to_int : (string, int) => option(int)
-    to_int(s, 10) = to_int_(List.reverse(StringInternal.to_list(s)), ch_to_int_10, 0, 1, 10)
-    to_int(s, 16) = to_int_(List.reverse(StringInternal.to_list(s)), ch_to_int_16, 0, 1, 16)
+  function tokens(s : string, pat : string) =
+    require(pat != "", "String.tokens: empty pattern")
+    tokens_(StringInternal.to_list(pat), StringInternal.to_list(s), [])
 
-  function
+  function to_int(s : string) : option(int) =
+    let s = StringInternal.to_list(s)
+    switch(is_prefix(['-'], s))
+      None    => to_int_pos(s)
+      Some(s) => switch(to_int_pos(s))
+                   None => None
+                   Some(x) => Some(-x)
+
+  private function to_int_pos(s : list(char)) =
+    switch(is_prefix(['0', 'x'], s))
+      None =>
+        to_int_(s, ch_to_int_10, 0, 10)
+      Some(s) =>
+        to_int_(s, ch_to_int_16, 0, 16)
+
+  private function
     tokens_(_, [], acc) = [StringInternal.from_list(List.reverse(acc))]
     tokens_(pat, str, acc) =
       switch(is_prefix(pat, str))
@@ -48,36 +59,36 @@ namespace String =
           let c :: cs = str
           tokens_(pat, cs, c :: acc)
 
-  function contains_(ix, lix, str, substr) =
-    if(ix > lix) None
-    else
+  private function
+    contains_(_, [], _) = None
+    contains_(ix, str, substr) =
       switch(is_prefix(substr, str))
         None =>
           let _ :: str = str
-          contains_(ix + 1, lix, str, substr)
+          contains_(ix + 1, str, substr)
         Some(_) =>
           Some(ix)
 
-  function
+  private function
     is_prefix([], ys) = Some(ys)
     is_prefix(_, [])  = None
     is_prefix(x :: xs, y :: ys) =
       if(x == y) is_prefix(xs, ys)
       else       None
 
-  function
-    to_int_([], _, x, _, _) = Some(x)
-    to_int_(i :: is, c, x, t, f) =
-      switch(c(i))
+  private function
+    to_int_([], _, x, _) = Some(x)
+    to_int_(i :: is, value, x, b) =
+      switch(value(i))
         None => None
-        Some(i) => to_int_(is, c, x + t * i, t * f, f)
+        Some(i) => to_int_(is, value, x * b + i, b)
 
-  function ch_to_int_10(c) =
+  private function ch_to_int_10(c) =
     let c = Char.to_int(c)
     if(c >= 48 && c =< 57) Some(c - 48)
     else None
 
-  function ch_to_int_16(c) =
+  private function ch_to_int_16(c) =
     let c = Char.to_int(c)
     if(c >= 48 && c =< 57)    Some(c - 48)
     elif(c >= 65 && c =< 70)  Some(c - 55)