diff --git a/src/comp/rustc.rc b/src/comp/rustc.rc
index c9f0d2f067b..aa88d1d4a88 100644
--- a/src/comp/rustc.rc
+++ b/src/comp/rustc.rc
@@ -63,6 +63,7 @@ mod syntax {
         mod expand;
 
         mod fmt;
+        mod ifmt;
         mod env;
         mod simplext;
         mod concat_idents;
diff --git a/src/comp/syntax/ext/base.rs b/src/comp/syntax/ext/base.rs
index 24efb38be86..2dade422c75 100644
--- a/src/comp/syntax/ext/base.rs
+++ b/src/comp/syntax/ext/base.rs
@@ -23,6 +23,7 @@ tag syntax_extension {
 fn syntax_expander_table() -> hashmap<istr, syntax_extension> {
     let syntax_expanders = new_str_hash::<syntax_extension>();
     syntax_expanders.insert(~"fmt", normal(ext::fmt::expand_syntax_ext));
+    syntax_expanders.insert(~"ifmt", normal(ext::ifmt::expand_syntax_ext));
     syntax_expanders.insert(~"env", normal(ext::env::expand_syntax_ext));
     syntax_expanders.insert(~"macro",
                             macro_defining(ext::simplext::add_new_extension));
diff --git a/src/comp/syntax/ext/ifmt.rs b/src/comp/syntax/ext/ifmt.rs
new file mode 100644
index 00000000000..c1bd13ac01e
--- /dev/null
+++ b/src/comp/syntax/ext/ifmt.rs
@@ -0,0 +1,363 @@
+
+
+/*
+ * The compiler code necessary to support the #fmt extension.  Eventually this
+ * should all get sucked into either the standard library extfmt module or the
+ * compiler syntax extension plugin interface.
+ */
+import std::vec;
+import std::str;
+import std::istr;
+import std::option;
+import std::option::none;
+import std::option::some;
+import std::extifmt::ct::*;
+import base::*;
+import codemap::span;
+export expand_syntax_ext;
+
+fn expand_syntax_ext(cx: &ext_ctxt, sp: span, arg: @ast::expr,
+                     _body: &option::t<istr>) -> @ast::expr {
+    let args: [@ast::expr] =
+        alt arg.node {
+          ast::expr_vec(elts, _) { elts }
+          _ {
+            cx.span_fatal(sp, ~"#fmt requires arguments of the form `[...]`.")
+          }
+        };
+    if vec::len::<@ast::expr>(args) == 0u {
+        cx.span_fatal(sp, ~"#fmt requires a format string");
+    }
+    let fmt =
+        expr_to_str(cx, args[0],
+                    ~"first argument to #fmt must be a "
+                    + ~"string literal.");
+    let fmtspan = args[0].span;
+    log "Format string:";
+    log fmt;
+    fn parse_fmt_err_(cx: &ext_ctxt, sp: span, msg: &istr) -> ! {
+        cx.span_fatal(sp, msg);
+    }
+    let parse_fmt_err = bind parse_fmt_err_(cx, fmtspan, _);
+    let pieces = parse_fmt_string(fmt, parse_fmt_err);
+    ret pieces_to_expr(cx, sp, pieces, args);
+}
+
+// FIXME: A lot of these functions for producing expressions can probably
+// be factored out in common with other code that builds expressions.
+// FIXME: Cleanup the naming of these functions
+fn pieces_to_expr(cx: &ext_ctxt, sp: span, pieces: &[piece],
+                  args: &[@ast::expr]) -> @ast::expr {
+    fn make_new_lit(cx: &ext_ctxt, sp: span, lit: ast::lit_) -> @ast::expr {
+        let sp_lit = @{node: lit, span: sp};
+        ret @{id: cx.next_id(), node: ast::expr_lit(sp_lit), span: sp};
+    }
+    fn make_new_str(cx: &ext_ctxt, sp: span, s: &istr) -> @ast::expr {
+        let lit = ast::lit_str(s, ast::sk_unique);
+        ret make_new_lit(cx, sp, lit);
+    }
+    fn make_new_int(cx: &ext_ctxt, sp: span, i: int) -> @ast::expr {
+        let lit = ast::lit_int(i);
+        ret make_new_lit(cx, sp, lit);
+    }
+    fn make_new_uint(cx: &ext_ctxt, sp: span, u: uint) -> @ast::expr {
+        let lit = ast::lit_uint(u);
+        ret make_new_lit(cx, sp, lit);
+    }
+    fn make_add_expr(cx: &ext_ctxt, sp: span, lhs: @ast::expr,
+                     rhs: @ast::expr) -> @ast::expr {
+        let binexpr = ast::expr_binary(ast::add, lhs, rhs);
+        ret @{id: cx.next_id(), node: binexpr, span: sp};
+    }
+    fn make_path_expr(cx: &ext_ctxt, sp: span, idents: &[ast::ident]) ->
+       @ast::expr {
+        let path = {global: false, idents: idents, types: []};
+        let sp_path = {node: path, span: sp};
+        let pathexpr = ast::expr_path(sp_path);
+        ret @{id: cx.next_id(), node: pathexpr, span: sp};
+    }
+    fn make_vec_expr(cx: &ext_ctxt, sp: span, exprs: &[@ast::expr]) ->
+       @ast::expr {
+        let vecexpr = ast::expr_vec(exprs, ast::imm);
+        ret @{id: cx.next_id(), node: vecexpr, span: sp};
+    }
+    fn make_call(cx: &ext_ctxt, sp: span, fn_path: &[ast::ident],
+                 args: &[@ast::expr]) -> @ast::expr {
+        let pathexpr = make_path_expr(cx, sp, fn_path);
+        let callexpr = ast::expr_call(pathexpr, args);
+        ret @{id: cx.next_id(), node: callexpr, span: sp};
+    }
+    fn make_rec_expr(cx: &ext_ctxt, sp: span,
+                     fields: &[{ident: ast::ident, ex: @ast::expr}]) ->
+       @ast::expr {
+        let astfields: [ast::field] = [];
+        for field: {ident: ast::ident, ex: @ast::expr} in fields {
+            let ident = field.ident;
+            let val = field.ex;
+            let astfield =
+                {node: {mut: ast::imm, ident: ident, expr: val}, span: sp};
+            astfields += [astfield];
+        }
+        let recexpr = ast::expr_rec(astfields, option::none::<@ast::expr>);
+        ret @{id: cx.next_id(), node: recexpr, span: sp};
+    }
+    fn make_path_vec(cx: &ext_ctxt, ident: &ast::ident) -> [ast::ident] {
+        fn compiling_std(cx: &ext_ctxt) -> bool {
+            ret istr::find(cx.crate_file_name(), ~"std.rc") >= 0;
+        }
+        if compiling_std(cx) {
+            ret [~"extifmt", ~"rt", ident];
+        } else { ret [~"std", ~"extifmt", ~"rt", ident]; }
+    }
+    fn make_rt_path_expr(cx: &ext_ctxt, sp: span,
+                         ident: &istr) -> @ast::expr {
+        let path = make_path_vec(cx, ident);
+        ret make_path_expr(cx, sp, path);
+    }
+    // Produces an AST expression that represents a RT::conv record,
+    // which tells the RT::conv* functions how to perform the conversion
+
+    fn make_rt_conv_expr(cx: &ext_ctxt, sp: span, cnv: &conv) -> @ast::expr {
+        fn make_flags(cx: &ext_ctxt, sp: span, flags: &[flag]) -> @ast::expr {
+            let flagexprs: [@ast::expr] = [];
+            for f: flag in flags {
+                let fstr;
+                alt f {
+                  flag_left_justify. { fstr = ~"flag_left_justify"; }
+                  flag_left_zero_pad. { fstr = ~"flag_left_zero_pad"; }
+                  flag_space_for_sign. { fstr = ~"flag_space_for_sign"; }
+                  flag_sign_always. { fstr = ~"flag_sign_always"; }
+                  flag_alternate. { fstr = ~"flag_alternate"; }
+                }
+                flagexprs += [make_rt_path_expr(cx, sp, fstr)];
+            }
+            // FIXME: 0-length vectors can't have their type inferred
+            // through the rec that these flags are a member of, so
+            // this is a hack placeholder flag
+
+            if vec::len::<@ast::expr>(flagexprs) == 0u {
+                flagexprs += [make_rt_path_expr(cx, sp, ~"flag_none")];
+            }
+            ret make_vec_expr(cx, sp, flagexprs);
+        }
+        fn make_count(cx: &ext_ctxt, sp: span, cnt: &count) -> @ast::expr {
+            alt cnt {
+              count_implied. {
+                ret make_rt_path_expr(cx, sp, ~"count_implied");
+              }
+              count_is(c) {
+                let count_lit = make_new_int(cx, sp, c);
+                let count_is_path = make_path_vec(cx, ~"count_is");
+                let count_is_args = [count_lit];
+                ret make_call(cx, sp, count_is_path, count_is_args);
+              }
+              _ { cx.span_unimpl(sp, ~"unimplemented #fmt conversion"); }
+            }
+        }
+        fn make_ty(cx: &ext_ctxt, sp: span, t: &ty) -> @ast::expr {
+            let rt_type;
+            alt t {
+              ty_hex(c) {
+                alt c {
+                  case_upper. { rt_type = ~"ty_hex_upper"; }
+                  case_lower. { rt_type = ~"ty_hex_lower"; }
+                }
+              }
+              ty_bits. { rt_type = ~"ty_bits"; }
+              ty_octal. { rt_type = ~"ty_octal"; }
+              _ { rt_type = ~"ty_default"; }
+            }
+            ret make_rt_path_expr(cx, sp, rt_type);
+        }
+        fn make_conv_rec(cx: &ext_ctxt, sp: span, flags_expr: @ast::expr,
+                         width_expr: @ast::expr, precision_expr: @ast::expr,
+                         ty_expr: @ast::expr) -> @ast::expr {
+            ret make_rec_expr(cx, sp,
+                              [{ident: ~"flags", ex: flags_expr},
+                               {ident: ~"width", ex: width_expr},
+                               {ident: ~"precision", ex: precision_expr},
+                               {ident: ~"ty", ex: ty_expr}]);
+        }
+        let rt_conv_flags = make_flags(cx, sp, cnv.flags);
+        let rt_conv_width = make_count(cx, sp, cnv.width);
+        let rt_conv_precision = make_count(cx, sp, cnv.precision);
+        let rt_conv_ty = make_ty(cx, sp, cnv.ty);
+        ret make_conv_rec(cx, sp, rt_conv_flags, rt_conv_width,
+                          rt_conv_precision, rt_conv_ty);
+    }
+    fn make_conv_call(cx: &ext_ctxt, sp: span, conv_type: &istr,
+                      cnv: &conv, arg: @ast::expr) -> @ast::expr {
+        let fname = ~"conv_" + conv_type;
+        let path = make_path_vec(cx, fname);
+        let cnv_expr = make_rt_conv_expr(cx, sp, cnv);
+        let args = [cnv_expr, arg];
+        ret make_call(cx, arg.span, path, args);
+    }
+    fn make_new_conv(cx: &ext_ctxt, sp: span, cnv: conv, arg: @ast::expr) ->
+       @ast::expr {
+        // FIXME: Extract all this validation into extfmt::ct
+
+        fn is_signed_type(cnv: conv) -> bool {
+            alt cnv.ty {
+              ty_int(s) {
+                alt s { signed. { ret true; } unsigned. { ret false; } }
+              }
+              _ { ret false; }
+            }
+        }
+        let unsupported = ~"conversion not supported in #fmt string";
+        alt cnv.param {
+          option::none. { }
+          _ { cx.span_unimpl(sp, unsupported); }
+        }
+        for f: flag in cnv.flags {
+            alt f {
+              flag_left_justify. { }
+              flag_sign_always. {
+                if !is_signed_type(cnv) {
+                    cx.span_fatal(sp,
+                                  ~"+ flag only valid in " +
+                                      ~"signed #fmt conversion");
+                }
+              }
+              flag_space_for_sign. {
+                if !is_signed_type(cnv) {
+                    cx.span_fatal(sp,
+                                  ~"space flag only valid in " +
+                                      ~"signed #fmt conversions");
+                }
+              }
+              flag_left_zero_pad. { }
+              _ { cx.span_unimpl(sp, unsupported); }
+            }
+        }
+        alt cnv.width {
+          count_implied. { }
+          count_is(_) { }
+          _ { cx.span_unimpl(sp, unsupported); }
+        }
+        alt cnv.precision {
+          count_implied. { }
+          count_is(_) { }
+          _ { cx.span_unimpl(sp, unsupported); }
+        }
+        alt cnv.ty {
+          ty_str. { ret make_conv_call(cx, arg.span, ~"str", cnv, arg); }
+          ty_int(sign) {
+            alt sign {
+              signed. { ret make_conv_call(cx, arg.span, ~"int", cnv, arg); }
+              unsigned. {
+                ret make_conv_call(cx, arg.span, ~"uint", cnv, arg);
+              }
+            }
+          }
+          ty_bool. { ret make_conv_call(cx, arg.span, ~"bool", cnv, arg); }
+          ty_char. { ret make_conv_call(cx, arg.span, ~"char", cnv, arg); }
+          ty_hex(_) { ret make_conv_call(cx, arg.span, ~"uint", cnv, arg); }
+          ty_bits. { ret make_conv_call(cx, arg.span, ~"uint", cnv, arg); }
+          ty_octal. { ret make_conv_call(cx, arg.span, ~"uint", cnv, arg); }
+          _ { cx.span_unimpl(sp, unsupported); }
+        }
+    }
+    fn log_conv(c: conv) {
+        alt c.param {
+          some(p) {
+            log "param: "
+                + istr::to_estr(std::int::to_str(p, 10u));
+          }
+          _ { log "param: none"; }
+        }
+        for f: flag in c.flags {
+            alt f {
+              flag_left_justify. { log "flag: left justify"; }
+              flag_left_zero_pad. { log "flag: left zero pad"; }
+              flag_space_for_sign. { log "flag: left space pad"; }
+              flag_sign_always. { log "flag: sign always"; }
+              flag_alternate. { log "flag: alternate"; }
+            }
+        }
+        alt c.width {
+          count_is(i) { log "width: count is "
+              + istr::to_estr(std::int::to_str(i, 10u)); }
+          count_is_param(i) {
+            log "width: count is param "
+                + istr::to_estr(std::int::to_str(i, 10u));
+          }
+          count_is_next_param. { log "width: count is next param"; }
+          count_implied. { log "width: count is implied"; }
+        }
+        alt c.precision {
+          count_is(i) { log "prec: count is "
+              + istr::to_estr(std::int::to_str(i, 10u)); }
+          count_is_param(i) {
+            log "prec: count is param "
+                + istr::to_estr(std::int::to_str(i, 10u));
+          }
+          count_is_next_param. { log "prec: count is next param"; }
+          count_implied. { log "prec: count is implied"; }
+        }
+        alt c.ty {
+          ty_bool. { log "type: bool"; }
+          ty_str. { log "type: str"; }
+          ty_char. { log "type: char"; }
+          ty_int(s) {
+            alt s {
+              signed. { log "type: signed"; }
+              unsigned. { log "type: unsigned"; }
+            }
+          }
+          ty_bits. { log "type: bits"; }
+          ty_hex(cs) {
+            alt cs {
+              case_upper. { log "type: uhex"; }
+              case_lower. { log "type: lhex"; }
+            }
+          }
+          ty_octal. { log "type: octal"; }
+        }
+    }
+    let fmt_sp = args[0].span;
+    let n = 0u;
+    let tmp_expr = make_new_str(cx, sp, ~"");
+    let nargs = vec::len::<@ast::expr>(args);
+    for pc: piece in pieces {
+        alt pc {
+          piece_string(s) {
+            let s_expr = make_new_str(cx, fmt_sp, s);
+            tmp_expr = make_add_expr(cx, fmt_sp, tmp_expr, s_expr);
+          }
+          piece_conv(conv) {
+            n += 1u;
+            if n >= nargs {
+                cx.span_fatal(sp,
+                              ~"not enough arguments to #fmt " +
+                                  ~"for the given format string");
+            }
+            log "Building conversion:";
+            log_conv(conv);
+            let arg_expr = args[n];
+            let c_expr = make_new_conv(cx, fmt_sp, conv, arg_expr);
+            tmp_expr = make_add_expr(cx, fmt_sp, tmp_expr, c_expr);
+          }
+        }
+    }
+    let expected_nargs = n + 1u; // n conversions + the fmt string
+
+    if expected_nargs < nargs {
+        cx.span_fatal(
+            sp, istr::from_estr(
+            #fmt["too many arguments to #fmt. found %u, expected %u",
+                 nargs, expected_nargs]));
+    }
+    ret tmp_expr;
+}
+//
+// Local Variables:
+// mode: rust
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// compile-command: "make -k -C $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
+// End:
+//
diff --git a/src/lib/extifmt.rs b/src/lib/extifmt.rs
new file mode 100644
index 00000000000..ea602891868
--- /dev/null
+++ b/src/lib/extifmt.rs
@@ -0,0 +1,429 @@
+
+
+/* The 'fmt' extension is modeled on the posix printf system.
+ *
+ * A posix conversion ostensibly looks like this:
+ *
+ * %[parameter][flags][width][.precision][length]type
+ *
+ * Given the different numeric type bestiary we have, we omit the 'length'
+ * parameter and support slightly different conversions for 'type':
+ *
+ * %[parameter][flags][width][.precision]type
+ *
+ * we also only support translating-to-rust a tiny subset of the possible
+ * combinations at the moment.
+ */
+import option::none;
+import option::some;
+
+
+/*
+ * We have a 'ct' (compile-time) module that parses format strings into a
+ * sequence of conversions. From those conversions AST fragments are built
+ * that call into properly-typed functions in the 'rt' (run-time) module.
+ * Each of those run-time conversion functions accepts another conversion
+ * description that specifies how to format its output.
+ *
+ * The building of the AST is currently done in a module inside the compiler,
+ * but should migrate over here as the plugin interface is defined.
+ */
+
+// Functions used by the fmt extension at compile time
+mod ct {
+    tag signedness { signed; unsigned; }
+    tag caseness { case_upper; case_lower; }
+    tag ty {
+        ty_bool;
+        ty_str;
+        ty_char;
+        ty_int(signedness);
+        ty_bits;
+        ty_hex(caseness);
+        ty_octal;
+        // FIXME: More types
+    }
+    tag flag {
+        flag_left_justify;
+        flag_left_zero_pad;
+        flag_space_for_sign;
+        flag_sign_always;
+        flag_alternate;
+    }
+    tag count {
+        count_is(int);
+        count_is_param(int);
+        count_is_next_param;
+        count_implied;
+    }
+
+    // A formatted conversion from an expression to a string
+    type conv =
+        {param: option::t<int>,
+         flags: [flag],
+         width: count,
+         precision: count,
+         ty: ty};
+
+
+    // A fragment of the output sequence
+    tag piece { piece_string(istr); piece_conv(conv); }
+    type error_fn = fn(&istr) -> ! ;
+
+    fn parse_fmt_string(s: &istr, error: error_fn) -> [piece] {
+        let pieces: [piece] = [];
+        let lim = istr::byte_len(s);
+        let buf = ~"";
+        fn flush_buf(buf: &istr, pieces: &mutable [piece]) -> istr {
+            if istr::byte_len(buf) > 0u {
+                let piece = piece_string(buf);
+                pieces += [piece];
+            }
+            ret ~"";
+        }
+        let i = 0u;
+        while i < lim {
+            let curr = istr::substr(s, i, 1u);
+            if istr::eq(curr, ~"%") {
+                i += 1u;
+                if i >= lim {
+                    error(~"unterminated conversion at end of string");
+                }
+                let curr2 = istr::substr(s, i, 1u);
+                if istr::eq(curr2, ~"%") {
+                    i += 1u;
+                } else {
+                    buf = flush_buf(buf, pieces);
+                    let rs = parse_conversion(s, i, lim, error);
+                    pieces += [rs.piece];
+                    i = rs.next;
+                }
+            } else { buf += curr; i += 1u; }
+        }
+        buf = flush_buf(buf, pieces);
+        ret pieces;
+    }
+    fn peek_num(s: &istr, i: uint, lim: uint) ->
+       option::t<{num: uint, next: uint}> {
+        if i >= lim { ret none; }
+        let c = s[i];
+        if !('0' as u8 <= c && c <= '9' as u8) { ret option::none; }
+        let n = c - ('0' as u8) as uint;
+        ret alt peek_num(s, i + 1u, lim) {
+              none. { some({num: n, next: i + 1u}) }
+              some(next) {
+                let m = next.num;
+                let j = next.next;
+                some({num: n * 10u + m, next: j})
+              }
+            };
+    }
+    fn parse_conversion(s: &istr, i: uint, lim: uint, error: error_fn) ->
+       {piece: piece, next: uint} {
+        let parm = parse_parameter(s, i, lim);
+        let flags = parse_flags(s, parm.next, lim);
+        let width = parse_count(s, flags.next, lim);
+        let prec = parse_precision(s, width.next, lim);
+        let ty = parse_type(s, prec.next, lim, error);
+        ret {piece:
+                 piece_conv({param: parm.param,
+                             flags: flags.flags,
+                             width: width.count,
+                             precision: prec.count,
+                             ty: ty.ty}),
+             next: ty.next};
+    }
+    fn parse_parameter(s: &istr, i: uint, lim: uint) ->
+       {param: option::t<int>, next: uint} {
+        if i >= lim { ret {param: none, next: i}; }
+        let num = peek_num(s, i, lim);
+        ret alt num {
+              none. { {param: none, next: i} }
+              some(t) {
+                let n = t.num;
+                let j = t.next;
+                if j < lim && s[j] == '$' as u8 {
+                    {param: some(n as int), next: j + 1u}
+                } else { {param: none, next: i} }
+              }
+            };
+    }
+    fn parse_flags(s: &istr, i: uint, lim: uint) ->
+       {flags: [flag], next: uint} {
+        let noflags: [flag] = [];
+        if i >= lim { ret {flags: noflags, next: i}; }
+
+        // FIXME: This recursion generates illegal instructions if the return
+        // value isn't boxed. Only started happening after the ivec conversion
+        fn more_(f: flag, s: &istr, i: uint, lim: uint) ->
+           @{flags: [flag], next: uint} {
+            let next = parse_flags(s, i + 1u, lim);
+            let rest = next.flags;
+            let j = next.next;
+            let curr: [flag] = [f];
+            ret @{flags: curr + rest, next: j};
+        }
+        let more = bind more_(_, s, i, lim);
+        let f = s[i];
+        ret if f == '-' as u8 {
+                *more(flag_left_justify)
+            } else if f == '0' as u8 {
+                *more(flag_left_zero_pad)
+            } else if f == ' ' as u8 {
+                *more(flag_space_for_sign)
+            } else if f == '+' as u8 {
+                *more(flag_sign_always)
+            } else if f == '#' as u8 {
+                *more(flag_alternate)
+            } else { {flags: noflags, next: i} };
+    }
+    fn parse_count(s: &istr, i: uint,
+                   lim: uint) -> {count: count, next: uint} {
+        ret if i >= lim {
+                {count: count_implied, next: i}
+            } else if s[i] == '*' as u8 {
+                let param = parse_parameter(s, i + 1u, lim);
+                let j = param.next;
+                alt param.param {
+                  none. { {count: count_is_next_param, next: j} }
+                  some(n) { {count: count_is_param(n), next: j} }
+                }
+            } else {
+                let num = peek_num(s, i, lim);
+                alt num {
+                  none. { {count: count_implied, next: i} }
+                  some(num) {
+                    {count: count_is(num.num as int), next: num.next}
+                  }
+                }
+            };
+    }
+    fn parse_precision(s: &istr, i: uint, lim: uint) ->
+       {count: count, next: uint} {
+        ret if i >= lim {
+                {count: count_implied, next: i}
+            } else if s[i] == '.' as u8 {
+                let count = parse_count(s, i + 1u, lim);
+
+
+                // If there were no digits specified, i.e. the precision
+                // was ".", then the precision is 0
+                alt count.count {
+                  count_implied. { {count: count_is(0), next: count.next} }
+                  _ { count }
+                }
+            } else { {count: count_implied, next: i} };
+    }
+    fn parse_type(s: &istr, i: uint, lim: uint, error: error_fn) ->
+       {ty: ty, next: uint} {
+        if i >= lim { error(~"missing type in conversion"); }
+        let tstr = istr::substr(s, i, 1u);
+        // TODO: Do we really want two signed types here?
+        // How important is it to be printf compatible?
+        let t =
+            if istr::eq(tstr, ~"b") {
+                ty_bool
+            } else if istr::eq(tstr, ~"s") {
+                ty_str
+            } else if istr::eq(tstr, ~"c") {
+                ty_char
+            } else if istr::eq(tstr, ~"d") || istr::eq(tstr, ~"i") {
+                ty_int(signed)
+            } else if istr::eq(tstr, ~"u") {
+                ty_int(unsigned)
+            } else if istr::eq(tstr, ~"x") {
+                ty_hex(case_lower)
+            } else if istr::eq(tstr, ~"X") {
+                ty_hex(case_upper)
+            } else if istr::eq(tstr, ~"t") {
+                ty_bits
+            } else if istr::eq(tstr, ~"o") {
+                ty_octal
+            } else { error(~"unknown type in conversion: " + tstr) };
+        ret {ty: t, next: i + 1u};
+    }
+}
+
+
+// Functions used by the fmt extension at runtime. For now there are a lot of
+// decisions made a runtime. If it proves worthwhile then some of these
+// conditions can be evaluated at compile-time. For now though it's cleaner to
+// implement it this way, I think.
+mod rt {
+    tag flag {
+        flag_left_justify;
+        flag_left_zero_pad;
+        flag_space_for_sign;
+        flag_sign_always;
+        flag_alternate;
+
+
+        // FIXME: This is a hack to avoid creating 0-length vec exprs,
+        // which have some difficulty typechecking currently. See
+        // comments in front::extfmt::make_flags
+        flag_none;
+    }
+    tag count { count_is(int); count_implied; }
+    tag ty { ty_default; ty_bits; ty_hex_upper; ty_hex_lower; ty_octal; }
+
+    // FIXME: May not want to use a vector here for flags;
+    // instead just use a bool per flag
+    type conv = {flags: [flag], width: count, precision: count, ty: ty};
+
+    fn conv_int(cv: &conv, i: int) -> istr {
+        let radix = 10u;
+        let prec = get_int_precision(cv);
+        let s = int_to_str_prec(i, radix, prec);
+        if 0 <= i {
+            if have_flag(cv.flags, flag_sign_always) {
+                s = ~"+" + s;
+            } else if have_flag(cv.flags, flag_space_for_sign) {
+                s = ~" " + s;
+            }
+        }
+        ret pad(cv, s, pad_signed);
+    }
+    fn conv_uint(cv: &conv, u: uint) -> istr {
+        let prec = get_int_precision(cv);
+        let rs =
+            alt cv.ty {
+              ty_default. { uint_to_str_prec(u, 10u, prec) }
+              ty_hex_lower. { uint_to_str_prec(u, 16u, prec) }
+              ty_hex_upper. { istr::to_upper(uint_to_str_prec(u, 16u, prec)) }
+              ty_bits. { uint_to_str_prec(u, 2u, prec) }
+              ty_octal. { uint_to_str_prec(u, 8u, prec) }
+            };
+        ret pad(cv, rs, pad_unsigned);
+    }
+    fn conv_bool(cv: &conv, b: bool) -> istr {
+        let s = if b { ~"true" } else { ~"false" };
+        // run the boolean conversion through the string conversion logic,
+        // giving it the same rules for precision, etc.
+
+        ret conv_str(cv, s);
+    }
+    fn conv_char(cv: &conv, c: char) -> istr {
+        ret pad(cv, istr::from_char(c), pad_nozero);
+    }
+    fn conv_str(cv: &conv, s: &istr) -> istr {
+        // For strings, precision is the maximum characters
+        // displayed
+
+        // FIXME: substr works on bytes, not chars!
+        let unpadded =
+            alt cv.precision {
+              count_implied. { s }
+              count_is(max) {
+                if max as uint < istr::char_len(s) {
+                    istr::substr(s, 0u, max as uint)
+                } else { s }
+              }
+            };
+        ret pad(cv, unpadded, pad_nozero);
+    }
+
+    // Convert an int to string with minimum number of digits. If precision is
+    // 0 and num is 0 then the result is the empty string.
+    fn int_to_str_prec(num: int, radix: uint, prec: uint) -> istr {
+        ret if num < 0 {
+                ~"-" + uint_to_str_prec(-num as uint, radix, prec)
+            } else { uint_to_str_prec(num as uint, radix, prec) };
+    }
+
+    // Convert a uint to string with a minimum number of digits.  If precision
+    // is 0 and num is 0 then the result is the empty string. Could move this
+    // to uint: but it doesn't seem all that useful.
+    fn uint_to_str_prec(num: uint, radix: uint, prec: uint) -> istr {
+        ret if prec == 0u && num == 0u {
+                ~""
+            } else {
+                let s = uint::to_str(num, radix);
+                let len = istr::char_len(s);
+                if len < prec {
+                    let diff = prec - len;
+                    let pad = str_init_elt('0', diff);
+                    pad + s
+                } else { s }
+            };
+    }
+    fn get_int_precision(cv: &conv) -> uint {
+        ret alt cv.precision {
+              count_is(c) { c as uint }
+              count_implied. { 1u }
+            };
+    }
+
+    // FIXME: This might be useful in str: but needs to be utf8 safe first
+    fn str_init_elt(c: char, n_elts: uint) -> istr {
+        let svec = vec::init_elt::<u8>(c as u8, n_elts);
+
+        ret istr::unsafe_from_bytes(svec);
+    }
+    tag pad_mode { pad_signed; pad_unsigned; pad_nozero; }
+    fn pad(cv: &conv, s: &istr, mode: pad_mode) -> istr {
+        let uwidth;
+        alt cv.width {
+          count_implied. { ret s; }
+          count_is(width) {
+            // FIXME: Maybe width should be uint
+
+            uwidth = width as uint;
+          }
+        }
+        let strlen = istr::char_len(s);
+        if uwidth <= strlen { ret s; }
+        let padchar = ' ';
+        let diff = uwidth - strlen;
+        if have_flag(cv.flags, flag_left_justify) {
+            let padstr = str_init_elt(padchar, diff);
+            ret s + padstr;
+        }
+        let might_zero_pad = false;
+        let signed = false;
+        alt mode {
+          pad_nozero. {
+            // fallthrough
+
+          }
+          pad_signed. { might_zero_pad = true; signed = true; }
+          pad_unsigned. { might_zero_pad = true; }
+        }
+        fn have_precision(cv: &conv) -> bool {
+            ret alt cv.precision { count_implied. { false } _ { true } };
+        }
+        let zero_padding = false;
+        if might_zero_pad && have_flag(cv.flags, flag_left_zero_pad) &&
+               !have_precision(cv) {
+            padchar = '0';
+            zero_padding = true;
+        }
+        let padstr = str_init_elt(padchar, diff);
+        // This is completely heinous. If we have a signed value then
+        // potentially rip apart the intermediate result and insert some
+        // zeros. It may make sense to convert zero padding to a precision
+        // instead.
+
+        if signed && zero_padding && istr::byte_len(s) > 0u {
+            let head = s[0];
+            if head == '+' as u8 || head == '-' as u8 || head == ' ' as u8 {
+                let headstr = istr::unsafe_from_bytes([head]);
+                let bytelen = istr::byte_len(s);
+                let numpart = istr::substr(s, 1u, bytelen - 1u);
+                ret headstr + padstr + numpart;
+            }
+        }
+        ret padstr + s;
+    }
+    fn have_flag(flags: &[flag], f: flag) -> bool {
+        for candidate: flag in flags { if candidate == f { ret true; } }
+        ret false;
+    }
+}
+// Local Variables:
+// mode: rust;
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// compile-command: "make -k -C $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
+// End:
diff --git a/src/lib/std.rc b/src/lib/std.rc
index ffbf26b5928..d39f5004af1 100644
--- a/src/lib/std.rc
+++ b/src/lib/std.rc
@@ -86,6 +86,7 @@ mod sha1;
 mod ebml;
 mod ufind;
 mod extfmt;
+mod extifmt;
 mod box;
 mod getopts;
 mod time;
diff --git a/src/test/run-pass/syntax-extension-fmt.rs b/src/test/run-pass/syntax-extension-fmt.rs
index c241a68e7f1..9e103adcf60 100644
--- a/src/test/run-pass/syntax-extension-fmt.rs
+++ b/src/test/run-pass/syntax-extension-fmt.rs
@@ -1,17 +1,17 @@
 use std;
-import std::str;
+import std::istr;
 
-fn test(actual: str, expected: str) {
+fn test(actual: &istr, expected: &istr) {
     log actual;
     log expected;
-    assert (str::eq(actual, expected));
+    assert (istr::eq(actual, expected));
 }
 
 fn main() {
-    test(#fmt["hello %d friends and %s things", 10, "formatted"],
-         "hello 10 friends and formatted things");
+    test(#ifmt[~"hello %d friends and %s things", 10, ~"formatted"],
+         ~"hello 10 friends and formatted things");
 
-    test(#fmt["test"], "test");
+    test(#ifmt[~"test"], ~"test");
 
     // a quadratic optimization in LLVM (jump-threading) makes this test a
     // bit slow to compile unless we break it up
@@ -26,192 +26,192 @@ fn main() {
 fn part1() {
     // Simple tests for types
 
-    test(#fmt["%d", 1], "1");
-    test(#fmt["%i", 2], "2");
-    test(#fmt["%i", -1], "-1");
-    test(#fmt["%u", 10u], "10");
-    test(#fmt["%s", "test"], "test");
-    test(#fmt["%b", true], "true");
-    test(#fmt["%b", false], "false");
-    test(#fmt["%c", 'A'], "A");
-    test(#fmt["%x", 0xff_u], "ff");
-    test(#fmt["%X", 0x12ab_u], "12AB");
-    test(#fmt["%o", 10u], "12");
-    test(#fmt["%t", 0b11010101_u], "11010101");
+    test(#ifmt[~"%d", 1], ~"1");
+    test(#ifmt[~"%i", 2], ~"2");
+    test(#ifmt[~"%i", -1], ~"-1");
+    test(#ifmt[~"%u", 10u], ~"10");
+    test(#ifmt[~"%s", ~"test"], ~"test");
+    test(#ifmt[~"%b", true], ~"true");
+    test(#ifmt[~"%b", false], ~"false");
+    test(#ifmt[~"%c", 'A'], ~"A");
+    test(#ifmt[~"%x", 0xff_u], ~"ff");
+    test(#ifmt[~"%X", 0x12ab_u], ~"12AB");
+    test(#ifmt[~"%o", 10u], ~"12");
+    test(#ifmt[~"%t", 0b11010101_u], ~"11010101");
     // 32-bit limits
 
-    test(#fmt["%i", -2147483648], "-2147483648");
-    test(#fmt["%i", 2147483647], "2147483647");
-    test(#fmt["%u", 4294967295u], "4294967295");
-    test(#fmt["%x", 0xffffffff_u], "ffffffff");
-    test(#fmt["%o", 0xffffffff_u], "37777777777");
-    test(#fmt["%t", 0xffffffff_u], "11111111111111111111111111111111");
+    test(#ifmt[~"%i", -2147483648], ~"-2147483648");
+    test(#ifmt[~"%i", 2147483647], ~"2147483647");
+    test(#ifmt[~"%u", 4294967295u], ~"4294967295");
+    test(#ifmt[~"%x", 0xffffffff_u], ~"ffffffff");
+    test(#ifmt[~"%o", 0xffffffff_u], ~"37777777777");
+    test(#ifmt[~"%t", 0xffffffff_u], ~"11111111111111111111111111111111");
 }
 fn part2() {
     // Widths
 
-    test(#fmt["%1d", 500], "500");
-    test(#fmt["%10d", 500], "       500");
-    test(#fmt["%10d", -500], "      -500");
-    test(#fmt["%10u", 500u], "       500");
-    test(#fmt["%10s", "test"], "      test");
-    test(#fmt["%10b", true], "      true");
-    test(#fmt["%10x", 0xff_u], "        ff");
-    test(#fmt["%10X", 0xff_u], "        FF");
-    test(#fmt["%10o", 10u], "        12");
-    test(#fmt["%10t", 0xff_u], "  11111111");
-    test(#fmt["%10c", 'A'], "         A");
+    test(#ifmt[~"%1d", 500], ~"500");
+    test(#ifmt[~"%10d", 500], ~"       500");
+    test(#ifmt[~"%10d", -500], ~"      -500");
+    test(#ifmt[~"%10u", 500u], ~"       500");
+    test(#ifmt[~"%10s", ~"test"], ~"      test");
+    test(#ifmt[~"%10b", true], ~"      true");
+    test(#ifmt[~"%10x", 0xff_u], ~"        ff");
+    test(#ifmt[~"%10X", 0xff_u], ~"        FF");
+    test(#ifmt[~"%10o", 10u], ~"        12");
+    test(#ifmt[~"%10t", 0xff_u], ~"  11111111");
+    test(#ifmt[~"%10c", 'A'], ~"         A");
     // Left justify
 
-    test(#fmt["%-10d", 500], "500       ");
-    test(#fmt["%-10d", -500], "-500      ");
-    test(#fmt["%-10u", 500u], "500       ");
-    test(#fmt["%-10s", "test"], "test      ");
-    test(#fmt["%-10b", true], "true      ");
-    test(#fmt["%-10x", 0xff_u], "ff        ");
-    test(#fmt["%-10X", 0xff_u], "FF        ");
-    test(#fmt["%-10o", 10u], "12        ");
-    test(#fmt["%-10t", 0xff_u], "11111111  ");
-    test(#fmt["%-10c", 'A'], "A         ");
+    test(#ifmt[~"%-10d", 500], ~"500       ");
+    test(#ifmt[~"%-10d", -500], ~"-500      ");
+    test(#ifmt[~"%-10u", 500u], ~"500       ");
+    test(#ifmt[~"%-10s", ~"test"], ~"test      ");
+    test(#ifmt[~"%-10b", true], ~"true      ");
+    test(#ifmt[~"%-10x", 0xff_u], ~"ff        ");
+    test(#ifmt[~"%-10X", 0xff_u], ~"FF        ");
+    test(#ifmt[~"%-10o", 10u], ~"12        ");
+    test(#ifmt[~"%-10t", 0xff_u], ~"11111111  ");
+    test(#ifmt[~"%-10c", 'A'], ~"A         ");
 }
 
 fn part3() {
     // Precision
 
-    test(#fmt["%.d", 0], "");
-    test(#fmt["%.u", 0u], "");
-    test(#fmt["%.x", 0u], "");
-    test(#fmt["%.t", 0u], "");
-    test(#fmt["%.d", 10], "10");
-    test(#fmt["%.d", -10], "-10");
-    test(#fmt["%.u", 10u], "10");
-    test(#fmt["%.s", "test"], "");
-    test(#fmt["%.x", 127u], "7f");
-    test(#fmt["%.o", 10u], "12");
-    test(#fmt["%.t", 3u], "11");
-    test(#fmt["%.c", 'A'], "A");
-    test(#fmt["%.0d", 0], "");
-    test(#fmt["%.0u", 0u], "");
-    test(#fmt["%.0x", 0u], "");
-    test(#fmt["%.0t", 0u], "");
-    test(#fmt["%.0d", 10], "10");
-    test(#fmt["%.0d", -10], "-10");
-    test(#fmt["%.0u", 10u], "10");
-    test(#fmt["%.0s", "test"], "");
-    test(#fmt["%.0x", 127u], "7f");
-    test(#fmt["%.0o", 10u], "12");
-    test(#fmt["%.0t", 3u], "11");
-    test(#fmt["%.0c", 'A'], "A");
-    test(#fmt["%.1d", 0], "0");
-    test(#fmt["%.1u", 0u], "0");
-    test(#fmt["%.1x", 0u], "0");
-    test(#fmt["%.1t", 0u], "0");
-    test(#fmt["%.1d", 10], "10");
-    test(#fmt["%.1d", -10], "-10");
-    test(#fmt["%.1u", 10u], "10");
-    test(#fmt["%.1s", "test"], "t");
-    test(#fmt["%.1x", 127u], "7f");
-    test(#fmt["%.1o", 10u], "12");
-    test(#fmt["%.1t", 3u], "11");
-    test(#fmt["%.1c", 'A'], "A");
+    test(#ifmt[~"%.d", 0], ~"");
+    test(#ifmt[~"%.u", 0u], ~"");
+    test(#ifmt[~"%.x", 0u], ~"");
+    test(#ifmt[~"%.t", 0u], ~"");
+    test(#ifmt[~"%.d", 10], ~"10");
+    test(#ifmt[~"%.d", -10], ~"-10");
+    test(#ifmt[~"%.u", 10u], ~"10");
+    test(#ifmt[~"%.s", ~"test"], ~"");
+    test(#ifmt[~"%.x", 127u], ~"7f");
+    test(#ifmt[~"%.o", 10u], ~"12");
+    test(#ifmt[~"%.t", 3u], ~"11");
+    test(#ifmt[~"%.c", 'A'], ~"A");
+    test(#ifmt[~"%.0d", 0], ~"");
+    test(#ifmt[~"%.0u", 0u], ~"");
+    test(#ifmt[~"%.0x", 0u], ~"");
+    test(#ifmt[~"%.0t", 0u], ~"");
+    test(#ifmt[~"%.0d", 10], ~"10");
+    test(#ifmt[~"%.0d", -10], ~"-10");
+    test(#ifmt[~"%.0u", 10u], ~"10");
+    test(#ifmt[~"%.0s", ~"test"], ~"");
+    test(#ifmt[~"%.0x", 127u], ~"7f");
+    test(#ifmt[~"%.0o", 10u], ~"12");
+    test(#ifmt[~"%.0t", 3u], ~"11");
+    test(#ifmt[~"%.0c", 'A'], ~"A");
+    test(#ifmt[~"%.1d", 0], ~"0");
+    test(#ifmt[~"%.1u", 0u], ~"0");
+    test(#ifmt[~"%.1x", 0u], ~"0");
+    test(#ifmt[~"%.1t", 0u], ~"0");
+    test(#ifmt[~"%.1d", 10], ~"10");
+    test(#ifmt[~"%.1d", -10], ~"-10");
+    test(#ifmt[~"%.1u", 10u], ~"10");
+    test(#ifmt[~"%.1s", ~"test"], ~"t");
+    test(#ifmt[~"%.1x", 127u], ~"7f");
+    test(#ifmt[~"%.1o", 10u], ~"12");
+    test(#ifmt[~"%.1t", 3u], ~"11");
+    test(#ifmt[~"%.1c", 'A'], ~"A");
 }
 fn part4() {
-    test(#fmt["%.5d", 0], "00000");
-    test(#fmt["%.5u", 0u], "00000");
-    test(#fmt["%.5x", 0u], "00000");
-    test(#fmt["%.5t", 0u], "00000");
-    test(#fmt["%.5d", 10], "00010");
-    test(#fmt["%.5d", -10], "-00010");
-    test(#fmt["%.5u", 10u], "00010");
-    test(#fmt["%.5s", "test"], "test");
-    test(#fmt["%.5x", 127u], "0007f");
-    test(#fmt["%.5o", 10u], "00012");
-    test(#fmt["%.5t", 3u], "00011");
-    test(#fmt["%.5c", 'A'], "A");
+    test(#ifmt[~"%.5d", 0], ~"00000");
+    test(#ifmt[~"%.5u", 0u], ~"00000");
+    test(#ifmt[~"%.5x", 0u], ~"00000");
+    test(#ifmt[~"%.5t", 0u], ~"00000");
+    test(#ifmt[~"%.5d", 10], ~"00010");
+    test(#ifmt[~"%.5d", -10], ~"-00010");
+    test(#ifmt[~"%.5u", 10u], ~"00010");
+    test(#ifmt[~"%.5s", ~"test"], ~"test");
+    test(#ifmt[~"%.5x", 127u], ~"0007f");
+    test(#ifmt[~"%.5o", 10u], ~"00012");
+    test(#ifmt[~"%.5t", 3u], ~"00011");
+    test(#ifmt[~"%.5c", 'A'], ~"A");
     // Bool precision. I'm not sure if it's good or bad to have bool
     // conversions support precision - it's not standard printf so we
     // can do whatever. For now I'm making it behave the same as string
     // conversions.
 
-    test(#fmt["%.b", true], "");
-    test(#fmt["%.0b", true], "");
-    test(#fmt["%.1b", true], "t");
+    test(#ifmt[~"%.b", true], ~"");
+    test(#ifmt[~"%.0b", true], ~"");
+    test(#ifmt[~"%.1b", true], ~"t");
 }
 
 fn part5() {
     // Explicit + sign. Only for signed conversions
 
-    test(#fmt["%+d", 0], "+0");
-    test(#fmt["%+d", 1], "+1");
-    test(#fmt["%+d", -1], "-1");
+    test(#ifmt[~"%+d", 0], ~"+0");
+    test(#ifmt[~"%+d", 1], ~"+1");
+    test(#ifmt[~"%+d", -1], ~"-1");
     // Leave space for sign
 
-    test(#fmt["% d", 0], " 0");
-    test(#fmt["% d", 1], " 1");
-    test(#fmt["% d", -1], "-1");
+    test(#ifmt[~"% d", 0], ~" 0");
+    test(#ifmt[~"% d", 1], ~" 1");
+    test(#ifmt[~"% d", -1], ~"-1");
     // Plus overrides space
 
-    test(#fmt["% +d", 0], "+0");
-    test(#fmt["%+ d", 0], "+0");
+    test(#ifmt[~"% +d", 0], ~"+0");
+    test(#ifmt[~"%+ d", 0], ~"+0");
     // 0-padding
 
-    test(#fmt["%05d", 0], "00000");
-    test(#fmt["%05d", 1], "00001");
-    test(#fmt["%05d", -1], "-0001");
-    test(#fmt["%05u", 1u], "00001");
-    test(#fmt["%05x", 127u], "0007f");
-    test(#fmt["%05X", 127u], "0007F");
-    test(#fmt["%05o", 10u], "00012");
-    test(#fmt["%05t", 3u], "00011");
+    test(#ifmt[~"%05d", 0], ~"00000");
+    test(#ifmt[~"%05d", 1], ~"00001");
+    test(#ifmt[~"%05d", -1], ~"-0001");
+    test(#ifmt[~"%05u", 1u], ~"00001");
+    test(#ifmt[~"%05x", 127u], ~"0007f");
+    test(#ifmt[~"%05X", 127u], ~"0007F");
+    test(#ifmt[~"%05o", 10u], ~"00012");
+    test(#ifmt[~"%05t", 3u], ~"00011");
     // 0-padding a string is undefined but glibc does this:
 
-    test(#fmt["%05s", "test"], " test");
-    test(#fmt["%05c", 'A'], "    A");
-    test(#fmt["%05b", true], " true");
+    test(#ifmt[~"%05s", ~"test"], ~" test");
+    test(#ifmt[~"%05c", 'A'], ~"    A");
+    test(#ifmt[~"%05b", true], ~" true");
     // Left-justify overrides 0-padding
 
-    test(#fmt["%-05d", 0], "0    ");
-    test(#fmt["%-05d", 1], "1    ");
-    test(#fmt["%-05d", -1], "-1   ");
-    test(#fmt["%-05u", 1u], "1    ");
-    test(#fmt["%-05x", 127u], "7f   ");
-    test(#fmt["%-05X", 127u], "7F   ");
-    test(#fmt["%-05o", 10u], "12   ");
-    test(#fmt["%-05t", 3u], "11   ");
-    test(#fmt["%-05s", "test"], "test ");
-    test(#fmt["%-05c", 'A'], "A    ");
-    test(#fmt["%-05b", true], "true ");
+    test(#ifmt[~"%-05d", 0], ~"0    ");
+    test(#ifmt[~"%-05d", 1], ~"1    ");
+    test(#ifmt[~"%-05d", -1], ~"-1   ");
+    test(#ifmt[~"%-05u", 1u], ~"1    ");
+    test(#ifmt[~"%-05x", 127u], ~"7f   ");
+    test(#ifmt[~"%-05X", 127u], ~"7F   ");
+    test(#ifmt[~"%-05o", 10u], ~"12   ");
+    test(#ifmt[~"%-05t", 3u], ~"11   ");
+    test(#ifmt[~"%-05s", ~"test"], ~"test ");
+    test(#ifmt[~"%-05c", 'A'], ~"A    ");
+    test(#ifmt[~"%-05b", true], ~"true ");
 }
 fn part6() {
     // Precision overrides 0-padding
 
-    test(#fmt["%06.5d", 0], " 00000");
-    test(#fmt["%06.5u", 0u], " 00000");
-    test(#fmt["%06.5x", 0u], " 00000");
-    test(#fmt["%06.5d", 10], " 00010");
-    test(#fmt["%06.5d", -10], "-00010");
-    test(#fmt["%06.5u", 10u], " 00010");
-    test(#fmt["%06.5s", "test"], "  test");
-    test(#fmt["%06.5c", 'A'], "     A");
-    test(#fmt["%06.5x", 127u], " 0007f");
-    test(#fmt["%06.5X", 127u], " 0007F");
-    test(#fmt["%06.5o", 10u], " 00012");
+    test(#ifmt[~"%06.5d", 0], ~" 00000");
+    test(#ifmt[~"%06.5u", 0u], ~" 00000");
+    test(#ifmt[~"%06.5x", 0u], ~" 00000");
+    test(#ifmt[~"%06.5d", 10], ~" 00010");
+    test(#ifmt[~"%06.5d", -10], ~"-00010");
+    test(#ifmt[~"%06.5u", 10u], ~" 00010");
+    test(#ifmt[~"%06.5s", ~"test"], ~"  test");
+    test(#ifmt[~"%06.5c", 'A'], ~"     A");
+    test(#ifmt[~"%06.5x", 127u], ~" 0007f");
+    test(#ifmt[~"%06.5X", 127u], ~" 0007F");
+    test(#ifmt[~"%06.5o", 10u], ~" 00012");
     // Signed combinations
 
-    test(#fmt["% 5d", 1], "    1");
-    test(#fmt["% 5d", -1], "   -1");
-    test(#fmt["%+5d", 1], "   +1");
-    test(#fmt["%+5d", -1], "   -1");
-    test(#fmt["% 05d", 1], " 0001");
-    test(#fmt["% 05d", -1], "-0001");
-    test(#fmt["%+05d", 1], "+0001");
-    test(#fmt["%+05d", -1], "-0001");
-    test(#fmt["%- 5d", 1], " 1   ");
-    test(#fmt["%- 5d", -1], "-1   ");
-    test(#fmt["%-+5d", 1], "+1   ");
-    test(#fmt["%-+5d", -1], "-1   ");
-    test(#fmt["%- 05d", 1], " 1   ");
-    test(#fmt["%- 05d", -1], "-1   ");
-    test(#fmt["%-+05d", 1], "+1   ");
-    test(#fmt["%-+05d", -1], "-1   ");
+    test(#ifmt[~"% 5d", 1], ~"    1");
+    test(#ifmt[~"% 5d", -1], ~"   -1");
+    test(#ifmt[~"%+5d", 1], ~"   +1");
+    test(#ifmt[~"%+5d", -1], ~"   -1");
+    test(#ifmt[~"% 05d", 1], ~" 0001");
+    test(#ifmt[~"% 05d", -1], ~"-0001");
+    test(#ifmt[~"%+05d", 1], ~"+0001");
+    test(#ifmt[~"%+05d", -1], ~"-0001");
+    test(#ifmt[~"%- 5d", 1], ~" 1   ");
+    test(#ifmt[~"%- 5d", -1], ~"-1   ");
+    test(#ifmt[~"%-+5d", 1], ~"+1   ");
+    test(#ifmt[~"%-+5d", -1], ~"-1   ");
+    test(#ifmt[~"%- 05d", 1], ~" 1   ");
+    test(#ifmt[~"%- 05d", -1], ~"-1   ");
+    test(#ifmt[~"%-+05d", 1], ~"+1   ");
+    test(#ifmt[~"%-+05d", -1], ~"-1   ");
 }