672 lines
24 KiB
Rust
672 lines
24 KiB
Rust
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! This pretty-printer is a direct reimplementation of Philip Karlton's
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//! Mesa pretty-printer, as described in appendix A of
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//!
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//! STAN-CS-79-770: "Pretty Printing", by Derek C. Oppen.
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//! Stanford Department of Computer Science, 1979.
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//!
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//! The algorithm's aim is to break a stream into as few lines as possible
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//! while respecting the indentation-consistency requirements of the enclosing
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//! block, and avoiding breaking at silly places on block boundaries, for
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//! example, between "x" and ")" in "x)".
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//!
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//! I am implementing this algorithm because it comes with 20 pages of
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//! documentation explaining its theory, and because it addresses the set of
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//! concerns I've seen other pretty-printers fall down on. Weirdly. Even though
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//! it's 32 years old. What can I say?
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//!
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//! Despite some redundancies and quirks in the way it's implemented in that
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//! paper, I've opted to keep the implementation here as similar as I can,
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//! changing only what was blatantly wrong, a typo, or sufficiently
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//! non-idiomatic rust that it really stuck out.
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//!
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//! In particular you'll see a certain amount of churn related to INTEGER vs.
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//! CARDINAL in the Mesa implementation. Mesa apparently interconverts the two
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//! somewhat readily? In any case, I've used uint for indices-in-buffers and
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//! ints for character-sizes-and-indentation-offsets. This respects the need
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//! for ints to "go negative" while carrying a pending-calculation balance, and
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//! helps differentiate all the numbers flying around internally (slightly).
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//!
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//! I also inverted the indentation arithmetic used in the print stack, since
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//! the Mesa implementation (somewhat randomly) stores the offset on the print
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//! stack in terms of margin-col rather than col itself. I store col.
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//!
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//! I also implemented a small change in the String token, in that I store an
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//! explicit length for the string. For most tokens this is just the length of
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//! the accompanying string. But it's necessary to permit it to differ, for
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//! encoding things that are supposed to "go on their own line" -- certain
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//! classes of comment and blank-line -- where relying on adjacent
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//! hardbreak-like Break tokens with long blankness indication doesn't actually
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//! work. To see why, consider when there is a "thing that should be on its own
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//! line" between two long blocks, say functions. If you put a hardbreak after
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//! each function (or before each) and the breaking algorithm decides to break
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//! there anyways (because the functions themselves are long) you wind up with
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//! extra blank lines. If you don't put hardbreaks you can wind up with the
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//! "thing which should be on its own line" not getting its own line in the
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//! rare case of "really small functions" or such. This re-occurs with comments
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//! and explicit blank lines. So in those cases we use a string with a payload
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//! we want isolated to a line and an explicit length that's huge, surrounded
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//! by two zero-length breaks. The algorithm will try its best to fit it on a
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//! line (which it can't) and so naturally place the content on its own line to
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//! avoid combining it with other lines and making matters even worse.
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use std::io;
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use std::string::String;
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#[deriving(Clone, PartialEq)]
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pub enum Breaks {
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Consistent,
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Inconsistent,
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}
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#[deriving(Clone)]
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pub struct BreakToken {
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offset: int,
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blank_space: int
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}
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#[deriving(Clone)]
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pub struct BeginToken {
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offset: int,
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breaks: Breaks
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}
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#[deriving(Clone)]
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pub enum Token {
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String(String, int),
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Break(BreakToken),
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Begin(BeginToken),
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End,
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Eof,
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}
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impl Token {
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pub fn is_eof(&self) -> bool {
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match *self { Eof => true, _ => false }
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}
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pub fn is_hardbreak_tok(&self) -> bool {
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match *self {
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Break(BreakToken {
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offset: 0,
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blank_space: bs
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}) if bs == SIZE_INFINITY =>
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true,
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_ =>
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false
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}
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}
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}
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pub fn tok_str(t: Token) -> String {
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match t {
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String(s, len) => return format!("STR({},{})", s, len),
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Break(_) => return "BREAK".to_string(),
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Begin(_) => return "BEGIN".to_string(),
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End => return "END".to_string(),
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Eof => return "EOF".to_string()
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}
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}
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pub fn buf_str(toks: Vec<Token>,
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szs: Vec<int>,
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left: uint,
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right: uint,
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lim: uint)
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-> String {
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let n = toks.len();
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assert_eq!(n, szs.len());
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let mut i = left;
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let mut l = lim;
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let mut s = String::from_str("[");
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while i != right && l != 0u {
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l -= 1u;
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if i != left {
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s.push_str(", ");
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}
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s.push_str(format!("{}={}",
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szs.get(i),
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tok_str(toks.get(i).clone())).as_slice());
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i += 1u;
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i %= n;
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}
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s.push_char(']');
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return s.into_string();
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}
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pub enum PrintStackBreak {
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Fits,
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Broken(Breaks),
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}
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pub struct PrintStackElem {
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offset: int,
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pbreak: PrintStackBreak
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}
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static SIZE_INFINITY: int = 0xffff;
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pub fn mk_printer(out: Box<io::Writer+'static>, linewidth: uint) -> Printer {
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// Yes 3, it makes the ring buffers big enough to never
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// fall behind.
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let n: uint = 3 * linewidth;
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debug!("mk_printer {}", linewidth);
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let token: Vec<Token> = Vec::from_elem(n, Eof);
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let size: Vec<int> = Vec::from_elem(n, 0i);
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let scan_stack: Vec<uint> = Vec::from_elem(n, 0u);
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Printer {
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out: out,
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buf_len: n,
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margin: linewidth as int,
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space: linewidth as int,
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left: 0,
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right: 0,
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token: token,
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size: size,
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left_total: 0,
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right_total: 0,
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scan_stack: scan_stack,
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scan_stack_empty: true,
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top: 0,
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bottom: 0,
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print_stack: Vec::new(),
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pending_indentation: 0
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}
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}
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/// In case you do not have the paper, here is an explanation of what's going
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/// on.
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///
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/// There is a stream of input tokens flowing through this printer.
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///
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/// The printer buffers up to 3N tokens inside itself, where N is linewidth.
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/// Yes, linewidth is chars and tokens are multi-char, but in the worst
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/// case every token worth buffering is 1 char long, so it's ok.
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///
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/// Tokens are String, Break, and Begin/End to delimit blocks.
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///
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/// Begin tokens can carry an offset, saying "how far to indent when you break
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/// inside here", as well as a flag indicating "consistent" or "inconsistent"
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/// breaking. Consistent breaking means that after the first break, no attempt
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/// will be made to flow subsequent breaks together onto lines. Inconsistent
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/// is the opposite. Inconsistent breaking example would be, say:
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///
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/// foo(hello, there, good, friends)
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///
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/// breaking inconsistently to become
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///
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/// foo(hello, there
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/// good, friends);
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///
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/// whereas a consistent breaking would yield:
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///
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/// foo(hello,
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/// there
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/// good,
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/// friends);
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///
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/// That is, in the consistent-break blocks we value vertical alignment
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/// more than the ability to cram stuff onto a line. But in all cases if it
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/// can make a block a one-liner, it'll do so.
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///
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/// Carrying on with high-level logic:
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///
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/// The buffered tokens go through a ring-buffer, 'tokens'. The 'left' and
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/// 'right' indices denote the active portion of the ring buffer as well as
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/// describing hypothetical points-in-the-infinite-stream at most 3N tokens
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/// apart (i.e. "not wrapped to ring-buffer boundaries"). The paper will switch
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/// between using 'left' and 'right' terms to denote the wrapped-to-ring-buffer
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/// and point-in-infinite-stream senses freely.
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///
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/// There is a parallel ring buffer, 'size', that holds the calculated size of
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/// each token. Why calculated? Because for Begin/End pairs, the "size"
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/// includes everything between the pair. That is, the "size" of Begin is
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/// actually the sum of the sizes of everything between Begin and the paired
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/// End that follows. Since that is arbitrarily far in the future, 'size' is
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/// being rewritten regularly while the printer runs; in fact most of the
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/// machinery is here to work out 'size' entries on the fly (and give up when
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/// they're so obviously over-long that "infinity" is a good enough
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/// approximation for purposes of line breaking).
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///
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/// The "input side" of the printer is managed as an abstract process called
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/// SCAN, which uses 'scan_stack', 'scan_stack_empty', 'top' and 'bottom', to
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/// manage calculating 'size'. SCAN is, in other words, the process of
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/// calculating 'size' entries.
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///
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/// The "output side" of the printer is managed by an abstract process called
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/// PRINT, which uses 'print_stack', 'margin' and 'space' to figure out what to
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/// do with each token/size pair it consumes as it goes. It's trying to consume
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/// the entire buffered window, but can't output anything until the size is >=
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/// 0 (sizes are set to negative while they're pending calculation).
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///
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/// So SCAN takes input and buffers tokens and pending calculations, while
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/// PRINT gobbles up completed calculations and tokens from the buffer. The
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/// theory is that the two can never get more than 3N tokens apart, because
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/// once there's "obviously" too much data to fit on a line, in a size
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/// calculation, SCAN will write "infinity" to the size and let PRINT consume
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/// it.
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///
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/// In this implementation (following the paper, again) the SCAN process is
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/// the method called 'pretty_print', and the 'PRINT' process is the method
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/// called 'print'.
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pub struct Printer {
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pub out: Box<io::Writer+'static>,
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buf_len: uint,
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/// Width of lines we're constrained to
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margin: int,
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/// Number of spaces left on line
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space: int,
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/// Index of left side of input stream
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left: uint,
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/// Index of right side of input stream
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right: uint,
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/// Ring-buffer stream goes through
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token: Vec<Token> ,
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/// Ring-buffer of calculated sizes
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size: Vec<int> ,
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/// Running size of stream "...left"
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left_total: int,
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/// Running size of stream "...right"
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right_total: int,
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/// Pseudo-stack, really a ring too. Holds the
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/// primary-ring-buffers index of the Begin that started the
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/// current block, possibly with the most recent Break after that
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/// Begin (if there is any) on top of it. Stuff is flushed off the
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/// bottom as it becomes irrelevant due to the primary ring-buffer
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/// advancing.
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scan_stack: Vec<uint> ,
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/// Top==bottom disambiguator
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scan_stack_empty: bool,
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/// Index of top of scan_stack
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top: uint,
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/// Index of bottom of scan_stack
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bottom: uint,
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/// Stack of blocks-in-progress being flushed by print
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print_stack: Vec<PrintStackElem> ,
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/// Buffered indentation to avoid writing trailing whitespace
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pending_indentation: int,
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}
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impl Printer {
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pub fn last_token(&mut self) -> Token {
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(*self.token.get(self.right)).clone()
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}
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// be very careful with this!
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pub fn replace_last_token(&mut self, t: Token) {
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*self.token.get_mut(self.right) = t;
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}
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pub fn pretty_print(&mut self, t: Token) -> io::IoResult<()> {
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debug!("pp ~[{},{}]", self.left, self.right);
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match t {
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Eof => {
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if !self.scan_stack_empty {
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self.check_stack(0);
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let left = (*self.token.get(self.left)).clone();
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let left_size = *self.size.get(self.left);
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try!(self.advance_left(left, left_size));
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}
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self.indent(0);
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Ok(())
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}
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Begin(b) => {
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if self.scan_stack_empty {
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self.left_total = 1;
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self.right_total = 1;
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self.left = 0u;
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self.right = 0u;
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} else { self.advance_right(); }
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debug!("pp Begin({})/buffer ~[{},{}]",
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b.offset, self.left, self.right);
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*self.token.get_mut(self.right) = t;
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*self.size.get_mut(self.right) = -self.right_total;
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let right = self.right;
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self.scan_push(right);
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Ok(())
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}
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End => {
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if self.scan_stack_empty {
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debug!("pp End/print ~[{},{}]", self.left, self.right);
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self.print(t, 0)
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} else {
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debug!("pp End/buffer ~[{},{}]", self.left, self.right);
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self.advance_right();
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*self.token.get_mut(self.right) = t;
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*self.size.get_mut(self.right) = -1;
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let right = self.right;
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self.scan_push(right);
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Ok(())
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}
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}
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Break(b) => {
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if self.scan_stack_empty {
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self.left_total = 1;
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self.right_total = 1;
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self.left = 0u;
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self.right = 0u;
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} else { self.advance_right(); }
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debug!("pp Break({})/buffer ~[{},{}]",
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b.offset, self.left, self.right);
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self.check_stack(0);
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let right = self.right;
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self.scan_push(right);
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*self.token.get_mut(self.right) = t;
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*self.size.get_mut(self.right) = -self.right_total;
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self.right_total += b.blank_space;
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Ok(())
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}
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String(ref s, len) => {
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if self.scan_stack_empty {
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debug!("pp String('{}')/print ~[{},{}]",
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*s, self.left, self.right);
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self.print(t.clone(), len)
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} else {
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debug!("pp String('{}')/buffer ~[{},{}]",
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*s, self.left, self.right);
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self.advance_right();
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*self.token.get_mut(self.right) = t.clone();
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*self.size.get_mut(self.right) = len;
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self.right_total += len;
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self.check_stream()
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}
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}
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}
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}
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pub fn check_stream(&mut self) -> io::IoResult<()> {
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debug!("check_stream ~[{}, {}] with left_total={}, right_total={}",
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self.left, self.right, self.left_total, self.right_total);
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if self.right_total - self.left_total > self.space {
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debug!("scan window is {}, longer than space on line ({})",
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self.right_total - self.left_total, self.space);
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if !self.scan_stack_empty {
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if self.left == *self.scan_stack.get(self.bottom) {
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debug!("setting {} to infinity and popping", self.left);
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let scanned = self.scan_pop_bottom();
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*self.size.get_mut(scanned) = SIZE_INFINITY;
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}
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}
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let left = (*self.token.get(self.left)).clone();
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let left_size = *self.size.get(self.left);
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try!(self.advance_left(left, left_size));
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if self.left != self.right {
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try!(self.check_stream());
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}
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}
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Ok(())
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}
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pub fn scan_push(&mut self, x: uint) {
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debug!("scan_push {}", x);
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if self.scan_stack_empty {
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self.scan_stack_empty = false;
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} else {
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self.top += 1u;
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self.top %= self.buf_len;
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assert!((self.top != self.bottom));
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}
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*self.scan_stack.get_mut(self.top) = x;
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}
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pub fn scan_pop(&mut self) -> uint {
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assert!((!self.scan_stack_empty));
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let x = *self.scan_stack.get(self.top);
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if self.top == self.bottom {
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self.scan_stack_empty = true;
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} else {
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self.top += self.buf_len - 1u; self.top %= self.buf_len;
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}
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return x;
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}
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pub fn scan_top(&mut self) -> uint {
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assert!((!self.scan_stack_empty));
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return *self.scan_stack.get(self.top);
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}
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pub fn scan_pop_bottom(&mut self) -> uint {
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assert!((!self.scan_stack_empty));
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let x = *self.scan_stack.get(self.bottom);
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if self.top == self.bottom {
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self.scan_stack_empty = true;
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} else {
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self.bottom += 1u; self.bottom %= self.buf_len;
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}
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return x;
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}
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pub fn advance_right(&mut self) {
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self.right += 1u;
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self.right %= self.buf_len;
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assert!((self.right != self.left));
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}
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pub fn advance_left(&mut self, x: Token, l: int) -> io::IoResult<()> {
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debug!("advance_left ~[{},{}], sizeof({})={}", self.left, self.right,
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self.left, l);
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if l >= 0 {
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let ret = self.print(x.clone(), l);
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match x {
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Break(b) => self.left_total += b.blank_space,
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String(_, len) => {
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assert_eq!(len, l); self.left_total += len;
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}
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_ => ()
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}
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if self.left != self.right {
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self.left += 1u;
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self.left %= self.buf_len;
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let left = (*self.token.get(self.left)).clone();
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let left_size = *self.size.get(self.left);
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try!(self.advance_left(left, left_size));
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}
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ret
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} else {
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Ok(())
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}
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}
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pub fn check_stack(&mut self, k: int) {
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if !self.scan_stack_empty {
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let x = self.scan_top();
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match self.token.get(x) {
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&Begin(_) => {
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if k > 0 {
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let popped = self.scan_pop();
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*self.size.get_mut(popped) = *self.size.get(x) +
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self.right_total;
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self.check_stack(k - 1);
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}
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}
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&End => {
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// paper says + not =, but that makes no sense.
|
|
let popped = self.scan_pop();
|
|
*self.size.get_mut(popped) = 1;
|
|
self.check_stack(k + 1);
|
|
}
|
|
_ => {
|
|
let popped = self.scan_pop();
|
|
*self.size.get_mut(popped) = *self.size.get(x) +
|
|
self.right_total;
|
|
if k > 0 {
|
|
self.check_stack(k);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
pub fn print_newline(&mut self, amount: int) -> io::IoResult<()> {
|
|
debug!("NEWLINE {}", amount);
|
|
let ret = write!(self.out, "\n");
|
|
self.pending_indentation = 0;
|
|
self.indent(amount);
|
|
return ret;
|
|
}
|
|
pub fn indent(&mut self, amount: int) {
|
|
debug!("INDENT {}", amount);
|
|
self.pending_indentation += amount;
|
|
}
|
|
pub fn get_top(&mut self) -> PrintStackElem {
|
|
let print_stack = &mut self.print_stack;
|
|
let n = print_stack.len();
|
|
if n != 0u {
|
|
*print_stack.get(n - 1u)
|
|
} else {
|
|
PrintStackElem {
|
|
offset: 0,
|
|
pbreak: Broken(Inconsistent)
|
|
}
|
|
}
|
|
}
|
|
pub fn print_str(&mut self, s: &str) -> io::IoResult<()> {
|
|
while self.pending_indentation > 0 {
|
|
try!(write!(self.out, " "));
|
|
self.pending_indentation -= 1;
|
|
}
|
|
write!(self.out, "{}", s)
|
|
}
|
|
pub fn print(&mut self, x: Token, l: int) -> io::IoResult<()> {
|
|
debug!("print {} {} (remaining line space={})", tok_str(x.clone()), l,
|
|
self.space);
|
|
debug!("{}", buf_str(self.token.clone(),
|
|
self.size.clone(),
|
|
self.left,
|
|
self.right,
|
|
6));
|
|
match x {
|
|
Begin(b) => {
|
|
if l > self.space {
|
|
let col = self.margin - self.space + b.offset;
|
|
debug!("print Begin -> push broken block at col {}", col);
|
|
self.print_stack.push(PrintStackElem {
|
|
offset: col,
|
|
pbreak: Broken(b.breaks)
|
|
});
|
|
} else {
|
|
debug!("print Begin -> push fitting block");
|
|
self.print_stack.push(PrintStackElem {
|
|
offset: 0,
|
|
pbreak: Fits
|
|
});
|
|
}
|
|
Ok(())
|
|
}
|
|
End => {
|
|
debug!("print End -> pop End");
|
|
let print_stack = &mut self.print_stack;
|
|
assert!((print_stack.len() != 0u));
|
|
print_stack.pop().unwrap();
|
|
Ok(())
|
|
}
|
|
Break(b) => {
|
|
let top = self.get_top();
|
|
match top.pbreak {
|
|
Fits => {
|
|
debug!("print Break({}) in fitting block", b.blank_space);
|
|
self.space -= b.blank_space;
|
|
self.indent(b.blank_space);
|
|
Ok(())
|
|
}
|
|
Broken(Consistent) => {
|
|
debug!("print Break({}+{}) in consistent block",
|
|
top.offset, b.offset);
|
|
let ret = self.print_newline(top.offset + b.offset);
|
|
self.space = self.margin - (top.offset + b.offset);
|
|
ret
|
|
}
|
|
Broken(Inconsistent) => {
|
|
if l > self.space {
|
|
debug!("print Break({}+{}) w/ newline in inconsistent",
|
|
top.offset, b.offset);
|
|
let ret = self.print_newline(top.offset + b.offset);
|
|
self.space = self.margin - (top.offset + b.offset);
|
|
ret
|
|
} else {
|
|
debug!("print Break({}) w/o newline in inconsistent",
|
|
b.blank_space);
|
|
self.indent(b.blank_space);
|
|
self.space -= b.blank_space;
|
|
Ok(())
|
|
}
|
|
}
|
|
}
|
|
}
|
|
String(s, len) => {
|
|
debug!("print String({})", s);
|
|
assert_eq!(l, len);
|
|
// assert!(l <= space);
|
|
self.space -= len;
|
|
self.print_str(s.as_slice())
|
|
}
|
|
Eof => {
|
|
// Eof should never get here.
|
|
fail!();
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Convenience functions to talk to the printer.
|
|
//
|
|
// "raw box"
|
|
pub fn rbox(p: &mut Printer, indent: uint, b: Breaks) -> io::IoResult<()> {
|
|
p.pretty_print(Begin(BeginToken {
|
|
offset: indent as int,
|
|
breaks: b
|
|
}))
|
|
}
|
|
|
|
pub fn ibox(p: &mut Printer, indent: uint) -> io::IoResult<()> {
|
|
rbox(p, indent, Inconsistent)
|
|
}
|
|
|
|
pub fn cbox(p: &mut Printer, indent: uint) -> io::IoResult<()> {
|
|
rbox(p, indent, Consistent)
|
|
}
|
|
|
|
pub fn break_offset(p: &mut Printer, n: uint, off: int) -> io::IoResult<()> {
|
|
p.pretty_print(Break(BreakToken {
|
|
offset: off,
|
|
blank_space: n as int
|
|
}))
|
|
}
|
|
|
|
pub fn end(p: &mut Printer) -> io::IoResult<()> { p.pretty_print(End) }
|
|
|
|
pub fn eof(p: &mut Printer) -> io::IoResult<()> { p.pretty_print(Eof) }
|
|
|
|
pub fn word(p: &mut Printer, wrd: &str) -> io::IoResult<()> {
|
|
p.pretty_print(String(/* bad */ wrd.to_string(), wrd.len() as int))
|
|
}
|
|
|
|
pub fn huge_word(p: &mut Printer, wrd: &str) -> io::IoResult<()> {
|
|
p.pretty_print(String(/* bad */ wrd.to_string(), SIZE_INFINITY))
|
|
}
|
|
|
|
pub fn zero_word(p: &mut Printer, wrd: &str) -> io::IoResult<()> {
|
|
p.pretty_print(String(/* bad */ wrd.to_string(), 0))
|
|
}
|
|
|
|
pub fn spaces(p: &mut Printer, n: uint) -> io::IoResult<()> {
|
|
break_offset(p, n, 0)
|
|
}
|
|
|
|
pub fn zerobreak(p: &mut Printer) -> io::IoResult<()> {
|
|
spaces(p, 0u)
|
|
}
|
|
|
|
pub fn space(p: &mut Printer) -> io::IoResult<()> {
|
|
spaces(p, 1u)
|
|
}
|
|
|
|
pub fn hardbreak(p: &mut Printer) -> io::IoResult<()> {
|
|
spaces(p, SIZE_INFINITY as uint)
|
|
}
|
|
|
|
pub fn hardbreak_tok_offset(off: int) -> Token {
|
|
Break(BreakToken {offset: off, blank_space: SIZE_INFINITY})
|
|
}
|
|
|
|
pub fn hardbreak_tok() -> Token { return hardbreak_tok_offset(0); }
|