From 109041fb2ea18893bea32a4743e995f0bc06d5aa Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Fri, 16 Mar 2018 20:39:47 -0700
Subject: quasilit: expose access to field formatting.

This is the second round of changes in perparation for
compiling the string quasiliterals special form.

Having split format_fields into a lower level do_format_field
and format_field, we now provide two functions which allow
Lisp code to call do_format_field.

The sys:fmt-simple function has fixed arguments for
the field width/alignment, indexing/slicing, separator
and plist.  Any of them can be defaulted with nil. This
function will be useful when the quasiliteral specifies
modifiers that are simple literals or constant expressions.
The sys:fmt-flex function takes a variable number of
arguments, after the object and the plist. This function
has to scan through the arguments and classify them
by type: a string is a separator, an integer is a width
and left/right alignment and so on. The compiler will use
sys:flex when format field modifiers are present whose
arguments contain expressions that get evaluated.

* eval.c (fmt_simple, fmt_flex): New static functions.
(eval_init): sys:fmt-simple and sys:fmt-flex registered.
---
 eval.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/eval.c b/eval.c
index 4cd431e2..bfcdae4d 100644
--- a/eval.c
+++ b/eval.c
@@ -2636,6 +2636,38 @@ val format_field(val obj, val modifier, val filter, val eval_fun)
   return do_format_field(obj, n, sep, range_ix, plist, filter);
 }
 
+static val fmt_simple(val obj, val n_in, val sep_in,
+                          val range_ix, val plist)
+{
+  val n = if3(null(n_in), zero, n_in);
+  val sep = if3(null(sep_in), lit(" "), sep_in);
+  return do_format_field(obj, n, sep, range_ix, plist, nil);
+}
+
+static val fmt_flex(val obj, val plist, struct args *args)
+{
+  cnum ix = 0;
+  val n = zero, sep = lit(" ");
+  val range_ix = nil;
+
+  while (args_more(args, ix)) {
+    val arg = args_get(args, &ix);
+
+    if (integerp(arg)) {
+      n = arg;
+    } else if (stringp(arg)) {
+      sep = arg;
+    } else if (rangep(arg)) {
+      if (to(arg))
+        range_ix = arg;
+      else
+        range_ix = from(arg);
+    }
+  }
+
+  return do_format_field(obj, n, sep, range_ix, plist, nil);
+}
+
 val subst_vars(val forms, val env, val filter)
 {
   list_collect_decl(out, iter);
@@ -6257,6 +6289,9 @@ void eval_init(void)
   reg_fun(intern(lit("tprint"), user_package), func_n2o(tprint, 1));
   reg_fun(intern(lit("display-width"), user_package), func_n1(display_width));
 
+  reg_fun(intern(lit("fmt-simple"), system_package), func_n5(fmt_simple));
+  reg_fun(intern(lit("fmt-flex"), system_package), func_n2v(fmt_flex));
+
   reg_varl(user_package_s = intern(lit("user-package"), user_package_var),
            user_package_var);
   reg_varl(system_package_s = intern(lit("system-package"), user_package_var),
-- 
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