From 479d988e420f99d94c9e28e5a178d18f9a8677ba Mon Sep 17 00:00:00 2001
From: Jan Nieuwenhuizen <janneke@gnu.org>
Date: Mon, 25 Jul 2016 00:06:18 +0200
Subject: [PATCH] mes.c: add set-cdr, substring, string-ref.

---
 mes.c    | 36 ++++++++++++++++++++++++++++++++++++
 scm.mes  |  1 +
 test.mes |  3 +++
 3 files changed, 40 insertions(+)

diff --git a/mes.c b/mes.c
index 133fb93c..93204ec5 100644
--- a/mes.c
+++ b/mes.c
@@ -187,6 +187,14 @@ pair_p (scm *x)
   return x->type == PAIR ? &scm_t : &scm_f;
 }
 
+scm *
+set_car_x (scm *x, scm *e)
+{
+  assert (x->type == PAIR);
+  x->car = e;
+  return &scm_unspecified;
+}
+
 scm *
 set_cdr_x (scm *x, scm *e)
 {
@@ -633,6 +641,34 @@ string_length (scm *x)
   return make_number (strlen (x->name));
 }
 
+scm *
+string_ref (scm *x, scm *k)
+{
+  assert (x->type == STRING);
+  assert (k->type == NUMBER);
+  return make_char (x->name[k->value]);
+}
+
+scm *
+substring (scm *x/*...*/)
+{
+  assert (x->type == PAIR);
+  assert (x->car->type == STRING);
+  char *s = x->car->name;
+  assert (x->cdr->car->type == NUMBER);
+  int start = x->cdr->car->value;
+  int end = strlen (s);
+  if (x->cdr->cdr->type == PAIR) {
+    assert (x->cdr->cdr->car->type == NUMBER);
+    assert (x->cdr->cdr->car->value <= end);
+    end = x->cdr->cdr->car->value;
+  }
+  char buf[256];
+  strncpy (buf, s+start, end - start);
+  buf[end-start] = 0;
+  return make_string (buf);
+}
+
 scm *
 length (scm *x)
 {
diff --git a/scm.mes b/scm.mes
index 0bbd4a39..0ecf363f 100755
--- a/scm.mes
+++ b/scm.mes
@@ -138,6 +138,7 @@
         #f)))
 
 (define assv assq)
+(define assv-ref assq-ref)
 
 (define (assoc key alist)
   (cond ((null? alist) #f)
diff --git a/test.mes b/test.mes
index ae525b93..02ff08f8 100644
--- a/test.mes
+++ b/test.mes
@@ -119,6 +119,9 @@
                      24))
 (pass-if "begin" (seq? (begin 'a 'b (+ 1 2)) 3))
 (pass-if "string-append" (sequal? (string-append "a" "b" "c") "abc"))
+(pass-if "substring" (sequal? (substring "hello world" 6) "world"))
+(pass-if "substring 2" (sequal? (substring "hello world" 4 7) "o w"))
+(pass-if "string-ref" (seq? (string-ref "hello world" 4) #\o))
 (pass-if "eq?" (not (eq? (string-append "a" "b" "c") "abc")))
 (pass-if "string-length" (seq? (string-length (string-append "a" "b" "c")) 3))
 (pass-if "char" (seq? (char->integer #\A) 65))