Add a pretty-printer

Adds a -pp option to the compiler which will cause it to simply
pretty-print the given file.

9 files changed, 1013 insertions, 25 deletions

diff --git a/src/comp/driver/rustc.rs b/src/comp/driver/rustc.rs
index 90fe0e0c..7ad0cdc7 100644
--- a/src/comp/driver/rustc.rs
+++ b/src/comp/driver/rustc.rs
@@ -61,6 +61,14 @@ impure fn compile_input(session.session sess,
     trans.trans_crate(sess, crate, output, shared);
 }
 
+impure fn pretty_print_input(session.session sess,
+                             eval.env env,
+                             str input) {
+    auto p = front.parser.new_parser(sess, env, 0, input);
+    auto crate = front.parser.parse_crate_from_source_file(p);
+    pretty.pprust.print_ast(crate.node.module);
+}
+
 fn warn_wrong_compiler() {
     log "This is the rust 'self-hosted' compiler.";
     log "The one written in rust.";
@@ -75,6 +83,7 @@ fn usage(session.session sess, str argv0) {
     log "    -o <filename>      write output to <filename>";
     log "    -nowarn            suppress wrong-compiler warning";
     log "    -shared            compile a shared-library crate";
+    log "    -pp                pretty-print the input instead of compiling";
     log "    -h                 display this message";
     log "";
     log "";
@@ -101,6 +110,7 @@ impure fn main(vec[str] args) {
     let option.t[str] output_file = none[str];
     let bool do_warn = true;
     let bool shared = false;
+    let bool pretty = false;
 
     auto i = 1u;
     auto len = _vec.len[str](args);
@@ -113,6 +123,8 @@ impure fn main(vec[str] args) {
                 do_warn = false;
             } else if (_str.eq(arg, "-shared")) {
                 shared = true;
+            } else if (_str.eq(arg, "-pp")) {
+                pretty = true;
             } else if (_str.eq(arg, "-o")) {
                 if (i+1u < len) {
                     output_file = some(args.(i+1u));
@@ -153,24 +165,27 @@ impure fn main(vec[str] args) {
         case (some[str](?ifile)) {
 
             auto env = default_environment(sess, args.(0), ifile);
-
-            alt (output_file) {
-                case (none[str]) {
-                    let vec[str] parts = _str.split(ifile, '.' as u8);
-                    parts = _vec.pop[str](parts);
-                    parts += ".bc";
-                    auto ofile = _str.concat(parts);
-                    compile_input(sess, env, ifile, ofile, shared);
-                }
-                case (some[str](?ofile)) {
-                    compile_input(sess, env, ifile, ofile, shared);
+            if (pretty) {
+                pretty_print_input(sess, env, ifile);
+            }
+            else {
+                alt (output_file) {
+                    case (none[str]) {
+                        let vec[str] parts = _str.split(ifile, '.' as u8);
+                        parts = _vec.pop[str](parts);
+                        parts += ".bc";
+                        auto ofile = _str.concat(parts);
+                        compile_input(sess, env, ifile, ofile, shared);
+                    }
+                    case (some[str](?ofile)) {
+                        compile_input(sess, env, ifile, ofile, shared);
+                    }
                 }
             }
         }
     }
 }
 
-
 // Local Variables:
 // mode: rust
 // fill-column: 78;
diff --git a/src/comp/front/ast.rs b/src/comp/front/ast.rs
index ed1e2114..d45260f3 100644
--- a/src/comp/front/ast.rs
+++ b/src/comp/front/ast.rs
@@ -122,6 +122,31 @@ tag binop {
     gt;
 }
 
+fn binop_to_str(binop op) -> str {
+    alt (op) {
+        case (add) {ret "+";}
+        case (sub) {ret "-";}
+        case (mul) {ret "*";}
+        case (div) {ret "/";}
+        case (rem) {ret "%";}
+        case (and) {ret "&&";}
+        case (or) {ret "||";}
+        case (bitxor) {ret "^";}
+        case (bitand) {ret "&";}
+        case (bitor) {ret "|";}
+        case (lsl) {ret "<<";}
+        case (lsr) {ret ">>";}
+        case (asr) {ret ">>>";}
+        case (eq) {ret "==";}
+        case (lt) {ret "<";}
+        case (le) {ret "<=";}
+        case (ne) {ret "!=";}
+        case (ge) {ret ">=";}
+        case (gt) {ret ">";}
+    }
+}
+
+
 tag unop {
     box;
     deref;
@@ -131,6 +156,17 @@ tag unop {
     _mutable;
 }
 
+fn unop_to_str(unop op) -> str {
+    alt (op) {
+        case (box) {ret "@";}
+        case (deref) {ret "*";}
+        case (bitnot) {ret "~";}
+        case (not) {ret "!";}
+        case (neg) {ret "-";}
+        case (_mutable) {ret "mutable";}
+    }
+}
+
 tag mode {
     val;
     alias;
diff --git a/src/comp/front/parser.rs b/src/comp/front/parser.rs
index 6f3111c7..f60ff36b 100644
--- a/src/comp/front/parser.rs
+++ b/src/comp/front/parser.rs
@@ -983,6 +983,7 @@ impure fn parse_prefix_expr(parser p) -> @ast.expr {
 
 type op_spec = rec(token.token tok, ast.binop op, int prec);
 
+// FIXME make this a const, don't store it in parser state
 fn prec_table() -> vec[op_spec] {
     ret vec(rec(tok=token.BINOP(token.STAR), op=ast.mul, prec=11),
             rec(tok=token.BINOP(token.SLASH), op=ast.div, prec=11),
diff --git a/src/comp/front/pretty.rs b/src/comp/front/pretty.rs
index 267763e3..2fd58126 100644
--- a/src/comp/front/pretty.rs
+++ b/src/comp/front/pretty.rs
@@ -5,6 +5,8 @@ import std._vec;
 
 export print_expr;
 
+// FIXME this is superseded by ../pretty/pprust.rs. can it be dropped?
+
 fn unknown() -> str {
     ret "<unknown ast node>";
 }
diff --git a/src/comp/middle/ty.rs b/src/comp/middle/ty.rs
index 62d9a2f0..c33b5d8d 100644
--- a/src/comp/middle/ty.rs
+++ b/src/comp/middle/ty.rs
@@ -169,6 +169,8 @@ fn path_to_str(&ast.path pth) -> str {
     ret result;
 }
 
+// FIXME use the pretty-printer for this once it has a concept of an
+// abstract stream
 fn ty_to_str(&@t typ) -> str {
 
     fn fn_input_to_str(&rec(ast.mode mode, @t ty) input) -> str {
diff --git a/src/comp/pretty/pp.rs b/src/comp/pretty/pp.rs
new file mode 100644
index 00000000..43a9220f
--- /dev/null
+++ b/src/comp/pretty/pp.rs
@@ -0,0 +1,207 @@
+import std.io;
+import std._vec;
+import std._str;
+
+tag boxtype {box_h; box_v; box_hv; box_align;}
+tag contexttype {cx_h; cx_v;}
+
+tag token {
+  brk(uint);
+  word(str);
+  cword(str); // closing token
+  open(boxtype, uint);
+  close;
+}
+
+type context = rec(contexttype tp, uint indent);
+
+type ps = @rec(mutable vec[context] context,
+               uint width,
+               mutable vec[token] buffered,
+               mutable uint scandepth,
+               mutable uint bufferedcol,
+               mutable uint col,
+               mutable bool start_of_line);
+
+fn mkstate(uint width) -> ps {
+  let vec[context] stack = vec(rec(tp=cx_v, indent=0u));
+  let vec[token] buff = vec();
+  ret @rec(mutable context=stack,
+           width=width,
+           mutable buffered=buff,
+           mutable scandepth=0u,
+           mutable bufferedcol=0u,
+           mutable col=0u,
+           mutable start_of_line=true);
+}
+
+impure fn push_context(ps p, contexttype tp, uint indent) {
+  before_print(p, false);
+  p.context = _vec.push[context](p.context, rec(tp=tp, indent=base_indent(p)
+                                                + indent));
+}
+
+impure fn pop_context(ps p) {
+  p.context = _vec.pop[context](p.context);
+}
+
+impure fn add_token(ps p, token tok) {
+  if (p.scandepth == 0u) {do_token(p, tok);}
+  else {buffer_token(p, tok);}
+}
+
+impure fn buffer_token(ps p, token tok) {
+  p.buffered += vec(tok);
+  p.bufferedcol += token_size(tok);
+  alt (p.buffered.(0)) {
+    case (brk(_)) {
+      alt (tok) {
+        case (brk(_)) {
+          if (p.scandepth == 1u) {finish_break_scan(p);}
+        }
+        case (open(box_h,_)) {p.scandepth += 1u;}
+        case (open(_,_)) {finish_break_scan(p);}
+        case (close) {
+          p.scandepth -= 1u;
+          if (p.scandepth == 0u) {finish_break_scan(p);}
+        }
+        case (_) {}
+      }
+    }
+    case (open(_,_)) {
+      if (p.bufferedcol > p.width) {finish_block_scan(p, cx_v);}
+      else {
+        alt (tok) {
+          case (open(_,_)) {p.scandepth += 1u;}
+          case (close) {
+            p.scandepth -= 1u;
+            if (p.scandepth == 0u) {finish_block_scan(p, cx_h);}
+          }
+          case (_) {}
+        }
+      }
+    }
+  }
+}
+
+impure fn finish_block_scan(ps p, contexttype tp) {
+  auto indent;
+  alt (p.buffered.(0)){
+    case (open(box_hv,?ind)) {
+      indent = ind;
+    }
+    case (open(box_align, _)) {
+      indent = p.col - base_indent(p);
+    }
+  }
+  p.scandepth = 0u;
+  push_context(p, tp, indent);
+  for (token t in _vec.shift[token](p.buffered)) {add_token(p, t);}
+}
+
+impure fn finish_break_scan(ps p) {
+  if (p.bufferedcol > p.width) {
+    write_str("\n");
+    p.col = 0u;
+  }
+  else {
+    auto width;
+    alt (p.buffered.(0)) {case(brk(?w)) {width = w;}}
+    auto i = 0u;
+    while (i < width) {write_str(" "); i+=1u;}
+    p.col += width;
+  }
+  p.scandepth = 0u;
+  for (token t in _vec.shift[token](p.buffered)) {add_token(p, t);}
+}
+
+impure fn start_scan(ps p, token tok) {
+  p.buffered = vec(tok);
+  p.scandepth = 1u;
+  p.bufferedcol = p.col;
+}
+
+fn cur_context(ps p) -> context {
+  ret p.context.(_vec.len[context](p.context)-1u);
+}
+fn base_indent(ps p) -> uint {
+  auto i = _vec.len[context](p.context);
+  while (i > 0u) {
+    i -= 1u;
+    auto cx = p.context.(i);
+    if (cx.tp == cx_v) {ret cx.indent;}
+  }
+}
+
+impure fn do_token(ps p, token tok) {
+  alt (tok) {
+    case (brk(?sz)) {
+      alt (cur_context(p).tp) {
+        case (cx_h) {
+          before_print(p, false);
+          start_scan(p, tok);
+        }
+        case (cx_v) {
+          write_str("\n");
+          p.col = 0u;
+          p.start_of_line = true;
+        }
+      }
+    }
+    case (word(?w)) {
+      before_print(p, false);
+      write_str(w);
+      p.col += _str.byte_len(w); // TODO char_len
+    }
+    case (cword(?w)) {
+      before_print(p, true);
+      write_str(w);
+      p.col += _str.byte_len(w); // TODO char_len
+    }
+    case (open(?tp, ?indent)) {
+      alt (tp) {
+        case (box_hv) {start_scan(p, tok);}
+        case (box_align) {start_scan(p, tok);}
+        case (box_h) {push_context(p, cx_h, indent);}
+        case (box_v) {push_context(p, cx_v, indent);}
+      }
+    }
+    case (close) {pop_context(p);}
+  }
+}
+
+impure fn before_print(ps p, bool closing) {
+  if (p.start_of_line) {
+    p.start_of_line = false;
+    auto ind;
+    if (closing) {ind = base_indent(p);}
+    else {ind = cur_context(p).indent;}
+    p.col = ind;
+    while (ind > 0u) {write_str(" "); ind -= 1u;}
+  }
+}
+
+fn write_str(str s) {
+  io.writefd(1, _str.bytes(s));
+}
+
+fn token_size(token tok) -> uint {
+  alt (tok) {
+    case (brk(?sz)) {ret sz;}
+    case (word(?w)) {ret _str.byte_len(w);}
+    case (cword(?w)) {ret _str.byte_len(w);}
+    case (open(_, _)) {ret 0u;} // TODO exception for V blocks?
+    case (close) {ret 0u;}
+  }
+}
+
+impure fn box(ps p, uint indent) {add_token(p, open(box_hv, indent));}
+impure fn abox(ps p) {add_token(p, open(box_align, 0u));}
+impure fn vbox(ps p, uint indent) {add_token(p, open(box_v, indent));}
+impure fn hbox(ps p, uint indent) {add_token(p, open(box_h, indent));}
+impure fn end(ps p) {add_token(p, close);}
+impure fn wrd(ps p, str wrd) {add_token(p, word(wrd));}
+impure fn cwrd(ps p, str wrd) {add_token(p, cword(wrd));}
+impure fn space(ps p) {add_token(p, brk(1u));}
+impure fn spaces(ps p, uint n) {add_token(p, brk(n));}
+impure fn line(ps p) {add_token(p, brk(0u));}
diff --git a/src/comp/pretty/pprust.rs b/src/comp/pretty/pprust.rs
new file mode 100644
index 00000000..d10f5e7c
--- /dev/null
+++ b/src/comp/pretty/pprust.rs
@@ -0,0 +1,716 @@
+import std._vec;
+import std._str;
+import std.option;
+import front.ast;
+import pp.box; import pp.abox; import pp.vbox;
+import pp.end; import pp.wrd; import pp.space; import pp.line;
+import pp.ps;
+
+import foo = std.io;
+
+const uint indent_unit = 2u;
+const int as_prec = 5;
+
+impure fn print_ast(ast._mod _mod) {
+  auto s = pp.mkstate(80u);
+  for (@ast.view_item vitem in _mod.view_items) {print_view_item(s, vitem);}
+  line(s);
+  for (@ast.item item in _mod.items) {print_item(s, item);}
+}
+
+impure fn hbox(ps s) {
+  pp.hbox(s, indent_unit);
+}
+impure fn wrd1(ps s, str word) {
+  wrd(s, word);
+  space(s);
+}
+impure fn popen(ps s) {
+  wrd(s, "(");
+  abox(s);
+}
+impure fn pclose(ps s) {
+  end(s);
+  wrd(s, ")");
+}
+impure fn bopen(ps s) {
+  wrd1(s, "{");
+  vbox(s, indent_unit);
+  line(s);
+}
+impure fn bclose(ps s) {
+  end(s);
+  pp.cwrd(s, "}");
+}
+impure fn commasep[IN](ps s, vec[IN] elts, impure fn (ps, IN) op) {
+  auto first = true;
+  for (IN elt in elts) {
+    if (first) {first = false;}
+    else {wrd1(s, ",");}
+    op(s, elt);
+  }
+}
+
+impure fn print_type(ps s, @ast.ty ty) {
+  hbox(s);
+  alt (ty.node) {
+    case (ast.ty_nil) {wrd(s, "()");}
+    case (ast.ty_bool) {wrd(s, "bool");}
+    case (ast.ty_int) {wrd(s, "int");}
+    case (ast.ty_uint) {wrd(s, "uint");}
+    case (ast.ty_machine(?tm)) {wrd(s, util.common.ty_mach_to_str(tm));}
+    case (ast.ty_char) {wrd(s, "char");}
+    case (ast.ty_str) {wrd(s, "str");}
+    case (ast.ty_box(?t)) {wrd(s, "@"); print_type(s, t);}
+    case (ast.ty_vec(?t)) {wrd(s, "vec["); print_type(s, t); wrd(s, "]");}
+    case (ast.ty_type) {wrd(s, "type");}
+    case (ast.ty_tup(?elts)) {
+      wrd(s, "tup");
+      popen(s);
+      auto f = print_type;
+      commasep[@ast.ty](s, elts, f);
+      pclose(s);
+    }
+    case (ast.ty_rec(?fields)) {
+      wrd(s, "rec");
+      popen(s);
+      impure fn print_field(ps s, ast.ty_field f) {
+        hbox(s);
+        print_type(s, f.ty);
+        space(s);
+        wrd(s, f.ident);
+        end(s);
+      }
+      auto f = print_field;
+      commasep[ast.ty_field](s, fields, f);
+      pclose(s);
+    }
+    case (ast.ty_fn(?proto,?inputs,?output)) {
+      if (proto == ast.proto_fn) {wrd(s, "fn");}
+      else {wrd(s, "iter");}
+      popen(s);
+      impure fn print_arg(ps s, ast.ty_arg input) {
+        if (middle.ty.mode_is_alias(input.mode)) {wrd(s, "&");}
+        print_type(s, input.ty);
+      }
+      auto f = print_arg;
+      commasep[ast.ty_arg](s, inputs, f);
+      pclose(s);
+      if (output.node != ast.ty_nil) {
+        space(s);
+        hbox(s);
+        wrd1(s, "->");
+        print_type(s, output);
+        end(s);
+      }
+    }
+    case (ast.ty_path(?path,_)) {
+      print_path(s, path);
+    }
+    case (ast.ty_mutable(?t)) {
+      wrd1(s, "mutable");
+      print_type(s, t);
+    }
+  }
+  end(s);
+}
+
+impure fn print_item(ps s, @ast.item item) {
+  hbox(s);
+  alt (item.node) {
+    case (ast.item_const(?id, ?ty, ?expr, _, _)) {
+      wrd1(s, "const");
+      print_type(s, ty);
+      space(s);
+      wrd1(s, id);
+      wrd1(s, "=");
+      print_expr(s, expr);
+      wrd(s, ";");
+    }
+    case (ast.item_fn(?name,?_fn,?typarams,_,_)) {
+      print_fn(s, _fn.decl, name, typarams);
+      space(s);
+      print_block(s, _fn.body);
+    }
+    case (ast.item_mod(?id,?_mod,_)) {
+      wrd1(s, "mod");
+      wrd1(s, id);
+      bopen(s);
+      for (@ast.item itm in _mod.items) {print_item(s, itm);}
+      bclose(s);
+    }
+    case (ast.item_native_mod(?id,?nmod,_)) {
+      wrd1(s, "native");
+      alt (nmod.abi) {
+        case (ast.native_abi_rust) {wrd1(s, "\"rust\"");}
+        case (ast.native_abi_cdecl) {wrd1(s, "\"cdecl\"");}
+      }
+      wrd1(s, "mod");
+      wrd1(s, id);
+      bopen(s);
+      for (@ast.native_item item in nmod.items) {
+        hbox(s);
+        alt (item.node) {
+          case (ast.native_item_ty(?id,_)) {
+            wrd1(s, "type");
+            wrd(s, id);
+          }
+          case (ast.native_item_fn(?id,?decl,?typarams,_,_)) {
+            print_fn(s, decl, id, typarams);
+          }
+        }
+        wrd(s, ";");
+        end(s);
+      }
+      bclose(s);
+    }
+    case (ast.item_ty(?id,?ty,?params,_,_)) {
+      wrd1(s, "type");
+      wrd(s, id);
+      print_type_params(s, params);
+      space(s);
+      wrd1(s, "=");
+      print_type(s, ty);
+      wrd(s, ";");
+    }
+    case (ast.item_tag(?id,?variants,?params,_)) {
+      wrd1(s, "tag");
+      wrd(s, id);
+      print_type_params(s, params);
+      space(s);
+      bopen(s);
+      for (ast.variant v in variants) {
+        wrd(s, v.name);
+        if (_vec.len[ast.variant_arg](v.args) > 0u) {
+          popen(s);
+          impure fn print_variant_arg(ps s, ast.variant_arg arg) {
+            print_type(s, arg.ty);
+          }
+          auto f = print_variant_arg;
+          commasep[ast.variant_arg](s, v.args, f);
+          pclose(s);
+        }
+        wrd(s, ";");
+        line(s);
+      }
+      bclose(s);
+    }
+    case (ast.item_obj(?id,?_obj,?params,_,_)) {
+      wrd1(s, "obj");
+      wrd(s, id);
+      print_type_params(s, params);
+      popen(s);
+      impure fn print_field(ps s, ast.obj_field field) {
+        hbox(s);
+        print_type(s, field.ty);
+        space(s);
+        wrd(s, field.ident);
+        end(s);
+      }
+      auto f = print_field;
+      commasep[ast.obj_field](s, _obj.fields, f);
+      pclose(s);
+      space(s);
+      bopen(s);
+      for (@ast.method meth in _obj.methods) {
+        hbox(s);
+        let vec[ast.ty_param] typarams = vec();
+        print_fn(s, meth.node.meth.decl, meth.node.ident, typarams);
+        space(s);
+        print_block(s, meth.node.meth.body);
+        end(s);
+        line(s);
+      }
+      alt (_obj.dtor) {
+        case (option.some[ast.block](?dtor)) {
+          hbox(s);
+          wrd1(s, "close");
+          print_block(s, dtor);
+          end(s);
+          line(s);
+        }
+        case (_) {}
+      }
+      bclose(s);
+    }
+  }
+  end(s);
+  line(s);
+  line(s);
+}
+
+impure fn print_block(ps s, ast.block blk) {
+  bopen(s);
+  for (@ast.stmt st in blk.node.stmts) {
+    alt (st.node) {
+      case (ast.stmt_decl(?decl)) {print_decl(s, decl);}
+      case (ast.stmt_expr(?expr)) {print_expr(s, expr);}
+    }
+    if (front.parser.stmt_ends_with_semi(st)) {wrd(s, ";");}
+    line(s);
+  }
+  alt (blk.node.expr) {
+    case (option.some[@ast.expr](?expr)) {
+      print_expr(s, expr);
+      line(s);
+    }
+    case (_) {}
+  }
+  bclose(s);
+}
+
+impure fn print_literal(ps s, @ast.lit lit) {
+  alt (lit.node) {
+    case (ast.lit_str(?st)) {print_string(s, st);}
+    case (ast.lit_char(?ch)) {
+      wrd(s, "'" + escape_str(_str.from_bytes(vec(ch as u8)), '\'') + "'");
+    }
+    case (ast.lit_int(?val)) {
+      wrd(s, util.common.istr(val));
+    }
+    case (ast.lit_uint(?val)) { // TODO clipping? uistr?
+      wrd(s, util.common.istr(val as int) + "u");
+    }
+    case (ast.lit_mach_int(?mach,?val)) {
+      wrd(s, util.common.istr(val as int));
+      wrd(s, util.common.ty_mach_to_str(mach));
+    }
+    case (ast.lit_nil) {wrd(s, "()");}
+    case (ast.lit_bool(?val)) {
+      if (val) {wrd(s, "true");} else {wrd(s, "false");}
+    }
+  }
+}
+
+impure fn print_expr(ps s, @ast.expr expr) {
+  auto pe = print_expr;
+  hbox(s);
+  alt (expr.node) {
+    case (ast.expr_vec(?exprs,_)) {
+      wrd(s, "vec");
+      popen(s);
+      commasep[@ast.expr](s, exprs, pe);
+      pclose(s);
+    }
+    case (ast.expr_tup(?exprs,_)) {
+      impure fn printElt(ps s, ast.elt elt) {
+        hbox(s);
+        if (elt.mut == ast.mut) {wrd1(s, "mutable");}
+        print_expr(s, elt.expr);
+        end(s);
+      }
+      wrd(s, "tup");
+      popen(s);
+      auto f = printElt;
+      commasep[ast.elt](s, exprs, f);
+      pclose(s);
+    }
+    case (ast.expr_rec(?fields,_,_)) {
+      impure fn print_field(ps s, ast.field field) {
+        hbox(s);
+        if (field.mut == ast.mut) {wrd1(s, "mutable");}
+        wrd(s, field.ident);
+        wrd(s, "=");
+        print_expr(s, field.expr);
+        end(s);
+      }
+      wrd(s, "rec");
+      popen(s);
+      auto f = print_field;
+      commasep[ast.field](s, fields, f);
+      pclose(s);
+    }
+    case (ast.expr_call(?func,?args,_)) {
+      print_expr(s, func);
+      popen(s);
+      commasep[@ast.expr](s, args, pe);
+      pclose(s);
+    }
+    case (ast.expr_bind(?func,?args,_)) {
+      impure fn print_opt(ps s, option.t[@ast.expr] expr) {
+        alt (expr) {
+          case (option.some[@ast.expr](?expr)) {
+            print_expr(s, expr);
+          }
+          case (_) {wrd(s, "_");}
+        }
+      }
+      wrd1(s, "bind");
+      print_expr(s, func);
+      popen(s);
+      auto f = print_opt;
+      commasep[option.t[@ast.expr]](s, args, f);
+      pclose(s);
+    }
+    case (ast.expr_binary(?op,?lhs,?rhs,_)) {
+      auto prec = operator_prec(op);
+      print_maybe_parens(s, lhs, prec);
+      space(s);
+      wrd1(s, ast.binop_to_str(op));
+      print_maybe_parens(s, rhs, prec + 1);
+    }
+    case (ast.expr_unary(?op,?expr,_)) {
+      wrd(s, ast.unop_to_str(op));
+      if (op == ast._mutable) {space(s);}
+      print_expr(s, expr);
+    }
+    case (ast.expr_lit(?lit,_)) {
+      print_literal(s, lit);
+    }
+    case (ast.expr_cast(?expr,?ty,_)) {
+      print_maybe_parens(s, expr, as_prec);
+      space(s);
+      wrd1(s, "as");
+      print_type(s, ty);
+    }
+    case (ast.expr_if(?test,?block,?clauses,?_else,_)) {
+      impure fn print_clause(ps s, @ast.expr test, ast.block blk) {
+        wrd1(s, "if");
+        popen(s);
+        print_expr(s, test);
+        pclose(s);
+        space(s);
+        print_block(s, blk);
+      }
+      print_clause(s, test, block);
+      for (tup(@ast.expr, ast.block) clause in clauses) {
+        space(s);
+        wrd1(s, "else");
+        print_clause(s, clause._0, clause._1);
+      }
+      alt (_else) {
+        case (option.some[ast.block](?blk)) {
+          space(s);
+          wrd1(s, "else");
+          print_block(s, blk);
+        }
+      }
+    }
+    case (ast.expr_while(?test,?block,_)) {
+      wrd1(s, "while");
+      popen(s);
+      print_expr(s, test);
+      pclose(s);
+      space(s);
+      print_block(s, block);
+    }
+    case (ast.expr_for(?decl,?expr,?block,_)) {
+      wrd1(s, "for");
+      popen(s);
+      print_decl(s, decl);
+      space(s);
+      wrd1(s, "in");
+      print_expr(s, expr);
+      pclose(s);
+      space(s);
+      print_block(s, block);
+    }
+    case (ast.expr_for_each(?decl,?expr,?block,_)) {
+      wrd1(s, "for each");
+      popen(s);
+      print_decl(s, decl);
+      space(s);
+      wrd1(s, "in");
+      print_expr(s, expr);
+      space(s);
+      print_block(s, block);
+    }
+    case (ast.expr_do_while(?block,?expr,_)) {
+      wrd1(s, "do");
+      space(s);
+      print_block(s, block);
+      space(s);
+      wrd1(s, "while");
+      popen(s);
+      print_expr(s, expr);
+      pclose(s);
+    }
+    case (ast.expr_alt(?expr,?arms,_)) {
+      wrd1(s, "alt");
+      popen(s);
+      print_expr(s, expr);
+      pclose(s);
+      space(s);
+      bopen(s);
+      for (ast.arm arm in arms) {
+        hbox(s);
+        wrd1(s, "case");
+        popen(s);
+        print_pat(s, arm.pat);
+        pclose(s);
+        space(s);
+        print_block(s, arm.block);
+        end(s);
+        line(s);
+      }
+      bclose(s);
+    }
+    case (ast.expr_block(?block,_)) {
+      print_block(s, block);
+    }
+    case (ast.expr_assign(?lhs,?rhs,_)) {
+      print_expr(s, lhs);
+      space(s);
+      wrd1(s, "=");
+      print_expr(s, rhs);
+    }
+    case (ast.expr_assign_op(?op,?lhs,?rhs,_)) {
+      print_expr(s, lhs);
+      space(s);
+      wrd(s, ast.binop_to_str(op));
+      wrd1(s, "=");
+      print_expr(s, rhs);
+    }
+    case (ast.expr_field(?expr,?id,_)) {
+      print_expr(s, expr);
+      wrd(s, ".");
+      wrd(s, id);
+    }
+    case (ast.expr_index(?expr,?index,_)) {
+      print_expr(s, expr);
+      wrd(s, ".");
+      popen(s);
+      print_expr(s, index);
+      pclose(s);
+    }
+    case (ast.expr_path(?path,_,_)) {
+      print_path(s, path);
+    }
+    case (ast.expr_fail) {
+      wrd(s, "fail");
+    }
+    case (ast.expr_ret(?result)) {
+      wrd(s, "ret");
+      alt (result) {
+        case (option.some[@ast.expr](?expr)) {
+          space(s);
+          print_expr(s, expr);
+        }
+        case (_) {}
+      }
+    }
+    case (ast.expr_put(?result)) {
+      wrd(s, "put");
+      alt (result) {
+        case (option.some[@ast.expr](?expr)) {
+          space(s);
+          print_expr(s, expr);
+        }
+        case (_) {}
+      }
+    }
+    case (ast.expr_be(?result)) {
+      wrd1(s, "be");
+      print_expr(s, result);
+    }
+    case (ast.expr_log(?expr)) {
+      wrd1(s, "log");
+      print_expr(s, expr);
+    }
+    case (ast.expr_check_expr(?expr)) {
+      wrd1(s, "check");
+      print_expr(s, expr);
+    }
+    case (_) {wrd(s, "X");}
+    // TODO expr_ext(path, vec[@expr], option.t[@expr], @expr, ann);
+  }
+  end(s);
+}
+
+impure fn print_decl(ps s, @ast.decl decl) {
+  hbox(s);
+  alt (decl.node) {
+    case (ast.decl_local(?loc)) {
+      alt (loc.ty) {
+        case (option.some[@ast.ty](?ty)) {
+          wrd1(s, "let");
+          print_type(s, ty);
+          space(s);
+        }
+        case (_) {
+          wrd1(s, "auto");
+        }
+      }
+      wrd(s, loc.ident);
+      alt (loc.init) {
+        case (option.some[@ast.expr](?init)) {
+          space(s);
+          wrd1(s, "=");
+          print_expr(s, init);
+        }
+        case (_) {}
+      }
+    }
+    case (ast.decl_item(?item)) {
+      print_item(s, item);
+    }
+  }
+  end(s);
+}
+
+impure fn print_path(ps s, ast.path path) {
+  auto first = true;
+  for (str id in path.node.idents) {
+    if (first) {first = false;}
+    else {wrd(s, ".");}
+    wrd(s, id);
+  }
+  if (_vec.len[@ast.ty](path.node.types) > 0u) {
+    wrd(s, "[");
+    auto f = print_type;
+    commasep[@ast.ty](s, path.node.types, f);
+    wrd(s, "]");
+  }
+}
+
+impure fn print_pat(ps s, @ast.pat pat) {
+  alt (pat.node) {
+    case (ast.pat_wild(_)) {wrd(s, "_");}
+    case (ast.pat_bind(?id,_,_)) {wrd(s, "?" + id);}
+    case (ast.pat_lit(?lit,_)) {print_literal(s, lit);}
+    case (ast.pat_tag(?path,?args,_,_)) {
+      print_path(s, path);
+      if (_vec.len[@ast.pat](args) > 0u) {
+        popen(s);
+        auto f = print_pat;
+        commasep[@ast.pat](s, args, f);
+        pclose(s);
+      }
+    }
+  }
+}
+
+impure fn print_fn(ps s, ast.fn_decl decl, str name,
+                   vec[ast.ty_param] typarams) {
+  alt (decl.effect) {
+    case (ast.eff_impure) {wrd1(s, "impure");}
+    case (ast.eff_unsafe) {wrd1(s, "unsafe");}
+    case (_) {}
+  }
+  wrd1(s, "fn");
+  wrd(s, name);
+  print_type_params(s, typarams);
+  popen(s);
+  impure fn print_arg(ps s, ast.arg x) {
+    hbox(s);
+    print_type(s, x.ty);
+    space(s);
+    wrd(s, x.ident);
+    end(s);
+  }
+  auto f = print_arg;
+  commasep[ast.arg](s, decl.inputs, f);
+  pclose(s);
+  if (decl.output.node != ast.ty_nil) {
+    space(s);
+    hbox(s);
+    wrd1(s, "->");
+    print_type(s, decl.output);
+    end(s);
+  }
+}
+
+impure fn print_type_params(ps s, vec[ast.ty_param] params) {
+  if (_vec.len[ast.ty_param](params) > 0u) {
+    wrd(s, "[");
+    impure fn printParam(ps s, ast.ty_param param) {wrd(s, param.ident);}
+    auto f = printParam;
+    commasep[ast.ty_param](s, params, f);
+    wrd(s, "]");
+  }
+}
+
+impure fn print_view_item(ps s, @ast.view_item item) {
+  hbox(s);
+  alt (item.node) {
+    case (ast.view_item_use(?id,?mta,_)) {
+      wrd1(s, "use");
+      wrd(s, id);
+      if (_vec.len[@ast.meta_item](mta) > 0u) {
+        popen(s);
+        impure fn print_meta(ps s, @ast.meta_item item) {
+          hbox(s);
+          wrd1(s, item.node.name);
+          wrd1(s, "=");
+          print_string(s, item.node.value);
+          end(s);
+        }
+        auto f = print_meta;
+        commasep[@ast.meta_item](s, mta, f);
+        pclose(s);
+      }
+    }
+    case (ast.view_item_import(?id,?ids,_,_)) {
+      wrd1(s, "import");
+      if (!_str.eq(id, ids.(_vec.len[str](ids)-1u))) {
+        wrd1(s, id);
+        wrd1(s, "=");
+      }
+      auto first = true;
+      for (str elt in ids) {
+        if (first) {first = false;}
+        else {wrd(s, ".");}
+        wrd(s, elt);
+      }
+    }
+    case (ast.view_item_export(?id)) {
+      wrd1(s, "export");
+      wrd(s, id);
+    }
+  }
+  end(s);
+  wrd(s, ";");
+  line(s);
+}
+
+// FIXME: The fact that this builds up the table anew for every call is
+// not good. Eventually, table should be a const.
+fn operator_prec(ast.binop op) -> int {
+  for (front.parser.op_spec spec in front.parser.prec_table()) {
+    if (spec.op == op) {ret spec.prec;}
+  }
+  fail;
+}
+
+impure fn print_maybe_parens(ps s, @ast.expr expr, int outer_prec) {
+  auto add_them;
+  alt (expr.node) {
+    case (ast.expr_binary(?op,_,_,_)) {
+      add_them = operator_prec(op) < outer_prec;
+    }
+    case (ast.expr_cast(_,_,_)) {
+      add_them = as_prec < outer_prec;
+    }
+    case (_) {
+      add_them = false;
+    }
+  }
+  if (add_them) {popen(s);}
+  print_expr(s, expr);
+  if (add_them) {pclose(s);}
+}
+
+// TODO non-ascii
+fn escape_str(str st, char to_escape) -> str {
+  let str out = "";
+  auto len = _str.byte_len(st);
+  auto i = 0u;
+  while (i < len) {
+    alt (st.(i) as char) {
+      case ('\n') {out += "\\n";}
+      case ('\t') {out += "\\t";}
+      case ('\r') {out += "\\r";}
+      case ('\\') {out += "\\\\";}
+      case (?cur) {
+        if (cur == to_escape) {out += "\\";}
+        out += cur as u8;
+      }
+    }
+    i += 1u;
+  }
+  ret out;
+}
+
+impure fn print_string(ps s, str st) {
+  wrd(s, "\""); wrd(s, escape_str(st, '"')); wrd(s, "\"");
+}
diff --git a/src/comp/rustc.rc b/src/comp/rustc.rc
index 43a04117..e4833409 100644
--- a/src/comp/rustc.rc
+++ b/src/comp/rustc.rc
@@ -31,6 +31,11 @@ mod driver {
     mod session;
 }
 
+mod pretty {
+    mod pp;
+    mod pprust;
+}
+
 mod util {
     mod common;
 }
diff --git a/src/lib/io.rs b/src/lib/io.rs
index 9f428cee..0c4eb39e 100644
--- a/src/lib/io.rs
+++ b/src/lib/io.rs
@@ -91,24 +91,28 @@ tag fileflag {
     truncate;
 }
 
+fn writefd(int fd, vec[u8] v) {
+    auto len = _vec.len[u8](v);
+    auto count = 0u;
+    auto vbuf;
+    while (count < len) {
+        vbuf = _vec.buf_off[u8](v, count);
+        auto nout = os.libc.write(fd, vbuf, len);
+        if (nout < 0) {
+            log "error dumping buffer";
+            log sys.rustrt.last_os_error();
+            fail;
+        }
+        count += nout as uint;
+    }
+}
+
 fn new_buf_writer(str path, vec[fileflag] flags) -> buf_writer {
 
     state obj fd_buf_writer(int fd) {
 
         fn write(vec[u8] v) {
-            auto len = _vec.len[u8](v);
-            auto count = 0u;
-            auto vbuf;
-            while (count < len) {
-                vbuf = _vec.buf_off[u8](v, count);
-                auto nout = os.libc.write(fd, vbuf, len);
-                if (nout < 0) {
-                    log "error dumping buffer";
-                    log sys.rustrt.last_os_error();
-                    fail;
-                }
-                count += nout as uint;
-            }
+            writefd(fd, v);
         }
 
         drop {