From: adam <adam@megacz.com>
Date: Fri, 20 Apr 2007 02:58:19 +0000 (-0400)
Subject: add IndentingReader
X-Git-Url: http://git.megacz.com/?p=sbp.git;a=commitdiff_plain;h=83bcf9559e9338c906b3c262ce7a1ecca7ffe3ed

add IndentingReader

darcs-hash:20070420025819-5007d-7325ca7dfce9eb76f0bdcf219a129f33989a7e70.gz
---

diff --git a/src/edu/berkeley/sbp/misc/IndentingReader.java b/src/edu/berkeley/sbp/misc/IndentingReader.java
new file mode 100644
index 0000000..bd80aad
--- /dev/null
+++ b/src/edu/berkeley/sbp/misc/IndentingReader.java
@@ -0,0 +1,158 @@
+// Copyright 2007 all rights reserved; see LICENSE file for BSD-style license
+
+package edu.berkeley.sbp.misc;
+
+import java.util.*;
+import java.io.*;
+
+/**
+ *  This Reader inserts special characters into the stream to indicate
+ *  when the indentation level has increased or decreased.<p>
+ *  
+ *  Lines are separated by LF characters (ASCII/Unicode 0x0A).  The
+ *  indentation of a line is defined to be the number of contiguous
+ *  spaces (ASCII/Unicode 0x20).  A blank line is a line consisting
+ *  only of zero or more spaces.  <p>
+ *
+ *  If the indentation of the current line is <i>greater than</i> the
+ *  indentation of the most recent non-blank line, the last space
+ *  character of the current line's indentation will be <i>replaced
+ *  by</i> an <tt>updent</tt> character. (FIXME not quite right)<p>
+ *
+ *  If the indentation of the next non-blank line is <i>less than</i>
+ *  the indentation of the current line, one or more <tt>downdent</tt>
+ *  characters will be <i>inserted</i> immediately after the last
+ *  non-whitespace character on the current line. <p>
+ *
+ *  These rules have two goals:
+ *
+ *  <ul> <li> Whitespace never appears immediately after an
+ *            <tt>updent</tt> or immediately before a
+ *            <tt>downdent</tt>.  This simplifies grammars which are
+ *            based on these characters.
+ *
+ *       <li> Blank lines have no effect on the placement of
+ *            <tt>updent</tt> and <tt>downdent</tt>.
+ *
+ *       <li> Every non-space character from the original stream
+ *            appears in the modified stream.  Furthermore, these
+ *            characters appear at exactly the same row and column as
+ *            they did in the original stream.  This simplifies
+ *            debugging considerably.
+ *  </ul>
+ */
+public class IndentingReader extends Reader {
+
+    private final Reader r;
+    private final char updent;
+    private final char downdent;
+
+    public IndentingReader(Reader r, char updent, char downdent) {
+        this.r = r;
+        this.updent = updent;
+        this.downdent = downdent;
+        istack.add(0);
+    }
+
+    private boolean indenting = true;
+    private int indentation = 0;
+    private ArrayList<Integer> istack = new ArrayList<Integer>();
+    private ArrayList<Integer> blanks = new ArrayList<Integer>();
+    private int queuedIndentation = 0;
+    private int blankIndentation = 0;
+
+    private int _peek = -2;
+    public int _peek() throws IOException {
+        if (_peek == -2) _peek = r.read();
+        return _peek;
+    }
+    public int _read() throws IOException {
+        int ret = _peek();
+        _peek = -2;
+        return ret;
+    }
+
+    public int read() throws IOException {
+        while(true) {
+            int i = _peek();
+            if (i==-1 && istack.size() > 1) {
+                istack.remove(istack.size()-1);
+                return downdent;
+            }
+            if (i==-1) return -1;
+
+            char c = (char)i;
+
+            if (c=='\n') {
+                if (indenting) {
+                    blanks.add(indentation);
+                } else {
+                    blanks.add(0);
+                }
+                indenting=true;
+                indentation = 0;
+                _read();
+                continue;
+            }
+
+            if (indenting) {
+
+                // more indentation to consume
+                if (c==' ') { indentation++; _read(); continue; }
+
+                // reached end of whitespace; line has non-whitespace material
+                int last = istack.size()==0 ? -1 : istack.get(istack.size()-1);
+
+                // emit any required close-braces
+                if (indentation < last) {
+                    istack.remove(istack.size()-1);
+                    return downdent;
+                }
+
+                // emit \n and any blank lines
+                if (blankIndentation > 0) {
+                    blankIndentation--;
+                    return ' ';
+                }
+                if (blanks.size() > 0) {
+                    blankIndentation = blanks.remove(blanks.size()-1);
+                    return '\n';
+                }
+
+                if (queuedIndentation < indentation) {
+                    queuedIndentation++;
+
+                    // omit the last space of indentation if we're planning on emitting an open-brace
+                    if (queuedIndentation < indentation || !(indentation > last))
+                        return ' ';
+                }
+
+                // emit open-brace
+                if (indentation > last) {
+                    istack.add(indentation);
+                    return updent;
+                }
+
+                // done with indentation
+                indenting = false;
+                queuedIndentation = 0;
+            }
+            return _read();
+        }
+    }
+
+    public int read(char[] buf, int off, int len) throws IOException {
+        int numread = 0;
+        while(len>0) {
+            int ret = read();
+            if (ret==-1) break;
+            buf[off] = (char)ret;
+            off++;
+            len--;
+            numread++;
+        }
+        return (len>0 && numread==0) ? -1 : numread;
+    }
+    public void close() throws IOException { r.close(); }
+}
+