diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6f81061
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/it0-out0.diff
+/it1-out*
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..2907ad4
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,17 @@
+TEE :=
+
+run:
+	cat it1-in.lang0 | python3 it0-out.py $(if $(TEE),| tee,> ) it1-out0.py
+
+	cat it1-in.lang0 | python3 it1-out0.py $(if $(TEE),| tee,> ) it1-out1.py
+	diff it1-out0.py it1-out1.py > it1-out1.diff
+	cat it1-in.lang0 | python3 it1-out1.py $(if $(TEE),| tee,> ) it1-out2.py
+	diff it1-out1.py it1-out2.py > it1-out2.diff
+	cat it1-in.lang0 | python3 it1-out2.py $(if $(TEE),| tee,> ) it1-out3.py
+	diff it1-out2.py it1-out3.py > it1-out3.diff
+
+	# See how much our hand written code differs from resulting code
+	-diff it0-out.py it1-out0.py > it0-out0.diff
+
+clean:
+	-rm it1-out*
diff --git a/it0-out.py b/it0-out.py
new file mode 100644
index 0000000..6593f7e
--- /dev/null
+++ b/it0-out.py
@@ -0,0 +1,362 @@
+import os
+import sys
+
+def emit(string):
+    sys.stdout.write(string)
+
+def trace(header, value):
+    if os.environ.get('TRACE'):
+        sys.stderr.write(f'{header}={value!r}\n')
+
+eof = chr(0)
+eol = chr(10)
+quote = chr(34)
+PEEK = None
+LINE = 1
+
+def peek():
+    global PEEK
+
+    if PEEK is None:
+        char = sys.stdin.read(1)
+        trace('char', char)
+        if not char:
+            PEEK = eof
+        else:
+            PEEK = char
+
+    return PEEK
+
+def skip():
+    global LINE
+    global PEEK
+
+    if eol == PEEK:
+        LINE += 1
+
+    PEEK = None
+
+def skipchar(char):
+    global LINE
+    assert char == peek(), (LINE, char, peek())
+    skip()
+
+def lexident():
+    word = ''
+    while True:
+        char = peek()
+
+        if char < 'a' or char > 'z':
+            break
+
+        word += char
+        skip()
+
+    return word
+
+def parseconststring():
+    skipchar(quote)
+    emit(quote)
+
+    escaped = False
+    while True:
+        char = peek()
+        if char == eof:
+            break
+        if char == quote:
+            break
+
+        emit(char)
+
+        skip()
+
+    skipchar(quote)
+    emit(quote)
+
+def parseexprvarref():
+    var = lexident()
+    emit(var)
+
+def parseexprcall():
+    funcname = lexident()
+    emit(funcname)
+    emit('(')
+
+    first = True
+    while ' ' == peek():
+        skip()
+        if not first:
+            emit(', ')
+        if quote == peek():
+            parseconststring()
+        else:
+            parseexprvarref()
+        first = False
+
+    emit(')')
+
+def parsestatset(indent):
+    skipchar(' ')
+    var = lexident()
+    skipchar(' ')
+
+    emit('    ' * indent)
+    emit(var)
+    emit(' = ')
+
+    parseconststring()
+
+    emit(eol)
+    skipchar(eol)
+
+def parsestatcalc(indent):
+    skipchar(' ')
+    var = lexident()
+    skipchar(' ')
+
+    emit('    ' * indent)
+    emit(var)
+    emit(' = ')
+
+    parseexprcall()
+
+    emit(eol)
+    skipchar(eol)
+
+def parsestatif(indent):
+    skipchar(' ')
+    emit('    ' * indent)
+    emit('if ')
+    parseexprvarref()
+    emit(':\n')
+    skipchar(eol)
+
+    parseblock(indent + 1)
+
+def parsestatforever(indent):
+    emit('    ' * indent)
+    emit('while True:\n')
+    skipchar(eol)
+
+    parseblock(indent + 1)
+
+def parsestatbreak(indent):
+    emit('    ' * indent)
+    emit('break\n')
+    skipchar(eol)
+
+def parsestatreturn(indent):
+    emit('    ' * indent)
+    emit('return ')
+    if ' ' == peek():
+        skip()
+        parseexprvarref()
+    emit(eol)
+    skipchar(eol)
+
+def parsestatemit(indent):
+    skipchar(' ')
+    emit('    ' * indent)
+    emit('emit(')
+
+    if quote == peek():
+        parseconststring()
+    else:
+        parseexprvarref()
+    skipchar(eol)
+
+    emit(')\n')
+
+def parsestattrace(indent):
+    skipchar(' ')
+    emit('    ' * indent)
+    emit('trace("')
+
+    var_name = lexident()
+    skipchar(eol)
+
+    emit(var_name)
+    emit('", ')
+    emit(var_name)
+    emit(')\n')
+
+def parsestatskipchar(indent):
+    skipchar(' ')
+    emit('    ' * indent)
+    emit('skipchar(')
+    if quote == peek():
+        parseconststring()
+    else:
+        parseexprvarref()
+    emit(')\n')
+    skipchar(eol)
+
+def parsestat(indent):
+    call = lexident()
+    trace('call', call)
+
+    if call == "set":
+        parsestatset(indent)
+        return
+
+    if call == "calc":
+        parsestatcalc(indent)
+        return
+
+    if call == "if":
+        parsestatif(indent)
+        return
+
+    if call == "forever":
+        parsestatforever(indent)
+        return
+
+    if call == "break":
+        parsestatbreak(indent)
+        return
+
+    if call == "return":
+        parsestatreturn(indent)
+        return
+
+    if call == "emit":
+        parsestatemit(indent)
+        return
+
+    if call == "trace":
+        parsestattrace(indent)
+        return
+
+    if call == "skipchar":
+        parsestatskipchar(indent)
+        return
+
+    emit('    ' * indent)
+    emit(call)
+    emit('(')
+
+    first = True
+    while ' ' == peek():
+        skip()
+        if not first:
+            emit(", ")
+        if '"' == peek():
+            parseconststring()
+        else:
+            parseexprvarref()
+        first = False
+
+    skipchar(eol)
+
+    emit(')\n')
+
+def parseblock(indent):
+    while True:
+        while eol == peek():
+            skip()
+
+        for _ in range(indent - 1):
+            skipchar('\t')
+
+        if '/' == peek():
+            skip()
+            skipchar(eol)
+            break
+
+        skipchar('\t')
+
+        parsestat(indent)
+
+def parsefunc():
+    funcname = lexident()
+    trace('funcname', funcname)
+    emit('def ')
+    emit(funcname)
+    emit('(')
+
+    first = True
+    while ' ' == peek():
+        skip()
+        var = lexident()
+        if not first:
+            emit(", ")
+        emit(var)
+        first = False
+
+    skipchar(':')
+    skipchar(eol)
+
+    emit('):\n')
+
+    parseblock(1)
+
+    emit("\n")
+
+def emitheader():
+    emit("import os\n")
+    emit("import sys\n")
+    emit("\n")
+    emit("def eq(a, b):\n")
+    emit("    return a == b\n")
+    emit("\n")
+    emit("def lt(a, b):\n")
+    emit("    return a < b\n")
+    emit("\n")
+    emit("def addstringchar(a, b):\n")
+    emit("    return a + b\n")
+    emit("\n")
+    emit("def emit(string):\n")
+    emit("    sys.stdout.write(string)\n")
+    emit("\n")
+    emit("def trace(header, value):\n")
+    emit("    if os.environ.get('TRACE'):\n")
+    emit("        sys.stderr.write(f'{header}={value!r}\\n')\n")
+    emit("\n")
+    emit("eof = chr(0)\n")
+    emit("eol = chr(10)\n")
+    emit("quote = chr(34)\n")
+    emit("PEEK = None\n")
+    emit("LINE = 1\n")
+    emit("\n")
+    emit("def peek():\n")
+    emit("    global PEEK\n")
+    emit("    if PEEK is None:\n")
+    emit("        char = sys.stdin.read(1)\n")
+    emit("        trace('char', char)\n")
+    emit("        if not char:\n")
+    emit("            PEEK = eof\n")
+    emit("        else:\n")
+    emit("            PEEK = char\n")
+    emit("    return PEEK\n")
+    emit("\n")
+    emit("def skip():\n")
+    emit("    global LINE\n")
+    emit("    global PEEK\n")
+    emit("    if eol == PEEK:\n")
+    emit("        LINE += 1\n")
+    emit("    PEEK = None\n")
+    emit("\n")
+    emit("def skipchar(char):\n")
+    emit("    global LINE\n")
+    emit("    assert char == peek(), (LINE, char, peek())\n")
+    emit("    skip()\n")
+    emit("\n")
+
+def emitfooter():
+    emit("if __name__ == '__main__':\n")
+    emit("    main()\n")
+
+def main():
+    emitheader()
+    while True:
+        if eof == peek():
+            break
+
+        while eol == peek():
+            skip()
+
+        parsefunc()
+    emitfooter()
+
+if __name__ == '__main__':
+    main()
diff --git a/it1-in.lang0 b/it1-in.lang0
new file mode 100644
index 0000000..0c10e96
--- /dev/null
+++ b/it1-in.lang0
@@ -0,0 +1,413 @@
+increaseindent indent:
+	calc indent addstringchar indent " "
+	calc indent addstringchar indent " "
+	calc indent addstringchar indent " "
+	calc indent addstringchar indent " "
+	return indent
+/
+
+lexident:
+	set word ""
+	forever
+		calc char peek
+		calc isbeforea lt char "a"
+		if isbeforea
+			break
+		/
+		calc isafterz lt "z" char
+		if isafterz
+			break
+		/
+		calc word addstringchar word char
+		skip
+	/
+	return word
+/
+
+parseconststring:
+	skipchar quote
+	emit quote
+	forever
+		calc char peek
+		calc iseof eq char eof
+		if iseof
+			break
+		/
+		calc isquote eq char quote
+		if isquote
+			break
+		/
+		emit char
+		skip
+	/
+	skipchar quote
+	emit quote
+/
+
+parseexprvarref:
+	calc varname lexident
+	emit varname
+/
+
+parseexprcall:
+	calc funcname lexident
+	emit funcname
+	emit "("
+	set first "1"
+	forever
+		calc char peek
+		calc isspace eq char " "
+		calc isnotspace not isspace
+		if isnotspace
+			break
+		/
+		skip
+		calc isfirst eq first "1"
+		calc isnotfirst not isfirst
+		if isnotfirst
+			emit ", "
+		/
+		calc char peek
+		calc isquote eq char quote
+		calc isnotquote not isquote
+		if isquote
+			parseconststring
+		/
+		if isnotquote
+			parseexprvarref
+		/
+		set first "0"
+	/
+	emit ")"
+/
+
+parsestatset indent:
+	skipchar " "
+	calc var lexident
+	skipchar " "
+	emit indent
+	emit var
+	emit " = "
+	parseconststring
+	emit eol
+	skipchar eol
+/
+
+parsestatcalc indent:
+	skipchar " "
+	calc var lexident
+	skipchar " "
+	emit indent
+	emit var
+	emit " = "
+	parseexprcall
+	emit eol
+	skipchar eol
+/
+
+parsestatif indent:
+	skipchar " "
+	emit indent
+	emit "if "
+	parseexprvarref
+	emit ":\n"
+	skipchar eol
+	calc indent increaseindent indent
+	parseblock indent
+/
+
+parsestatforever indent:
+	emit indent
+	emit "while True:\n"
+	skipchar eol
+	calc indent increaseindent indent
+	parseblock indent
+/
+
+parsestatbreak indent:
+	emit indent
+	emit "break\n"
+	skipchar eol
+/
+
+parsestatreturn indent:
+	emit indent
+	emit "return "
+	calc char peek
+	calc isspace eq char " "
+	if isspace
+		skip
+		parseexprvarref
+	/
+	emit eol
+	skipchar eol
+/
+
+parsestatemit indent:
+	emit indent
+	emit "emit("
+	skipchar " "
+	calc char peek
+	calc isquote eq char quote
+	calc isnotquote not isquote
+	if isquote
+		parseconststring
+	/
+	if isnotquote
+		parseexprvarref
+	/
+	emit ")\n"
+	skipchar eol
+/
+
+parsestattrace indent:
+	emit indent
+	emit "trace("
+	emit quote
+	skipchar " "
+	calc varname lexident
+	emit varname
+	emit quote
+	emit ", "
+	emit varname
+	emit ")\n"
+	skipchar eol
+/
+
+parsestatskipchar indent:
+	skipchar " "
+	emit indent
+	emit "skipchar("
+	calc char peek
+	calc isquote eq char quote
+	calc isnotquote not isquote
+	if isquote
+		parseconststring
+	/
+	if isnotquote
+		parseexprvarref
+	/
+	emit ")\n"
+	skipchar eol
+/
+
+parsestat indent:
+	calc call lexident
+	trace call
+	calc isset eq call "set"
+	if isset
+		parsestatset indent
+		return
+	/
+	calc iscalc eq call "calc"
+	if iscalc
+		parsestatcalc indent
+		return
+	/
+	calc isif eq call "if"
+	if isif
+		parsestatif indent
+		return
+	/
+	calc isforever eq call "forever"
+	if isforever
+		parsestatforever indent
+		return
+	/
+	calc isbreak eq call "break"
+	if isbreak
+		parsestatbreak indent
+		return
+	/
+	calc isreturn eq call "return"
+	if isreturn
+		parsestatreturn indent
+		return
+	/
+	calc isemit eq call "emit"
+	if isemit
+		parsestatemit indent
+		return
+	/
+	calc istrace eq call "trace"
+	if istrace
+		parsestattrace indent
+		return
+	/
+	calc isskipchar eq call "skipchar"
+	if isskipchar
+		parsestatskipchar indent
+		return
+	/
+	emit indent
+	emit call
+	emit "("
+	set first "1"
+	forever
+		calc char peek
+		calc isspace eq char " "
+		calc isnotspace not isspace
+		if isnotspace
+			break
+		/
+		skip
+		calc char peek
+		calc isquote eq char quote
+		calc isnotquote not isquote
+		if isquote
+			parseconststring
+		/
+		if isnotquote
+			parseexprvarref
+		/
+		calc isfirst eq first "1"
+		calc isnotfirst not isfirst
+		if isnotfirst
+			emit ", "
+		/
+		set first "0"
+	/
+	skipchar eol
+	emit ")\n"
+/
+
+parseblock indent:
+	forever
+		forever
+			calc char peek
+			calc iseol eq char eol
+			calc isnoteol not iseol
+			if isnoteol
+				break
+			/
+			skip
+		/
+		set copy "    "
+		forever
+			calc isdone eq copy indent
+			if isdone
+				break
+			/
+			skipchar "\t"
+			calc copy increaseindent copy
+		/
+		calc char peek
+		calc iseoblock eq char "/"
+		if iseoblock
+			skip
+			skipchar eol
+			break
+		/
+		skipchar "\t"
+		parsestat indent
+	/
+/
+
+parsefunc:
+	calc funcname lexident
+	trace funcname
+	emit "def "
+	emit funcname
+	emit "("
+	set first "1"
+	forever
+		calc char peek
+		calc isspace eq char " "
+		calc isnotspace not isspace
+		if isnotspace
+			break
+		/
+		skip
+		calc var lexident
+		calc isfirst eq first "1"
+		calc isnotfirst not isfirst
+		if isnotfirst
+			emit ", "
+		/
+		emit var
+		set first "0"
+	/
+	skipchar ":"
+	skipchar eol
+	emit "):\n"
+	parseblock "    "
+	emit "\n"
+/
+
+emitheader:
+	emit "import os\n"
+	emit "import sys\n"
+	emit "\n"
+	emit "def eq(a, b):\n"
+	emit "    return a == b\n"
+	emit "\n"
+	emit "def lt(a, b):\n"
+	emit "    return a < b\n"
+	emit "\n"
+	emit "def addstringchar(a, b):\n"
+	emit "    return a + b\n"
+	emit "\n"
+	emit "def emit(string):\n"
+	emit "    sys.stdout.write(string)\n"
+	emit "\n"
+	emit "def trace(header, value):\n"
+	emit "    if os.environ.get('TRACE'):\n"
+	emit "        sys.stderr.write(f'{header}={value!r}\\n')\n"
+	emit "\n"
+	emit "eof = chr(0)\n"
+	emit "eol = chr(10)\n"
+	emit "quote = chr(34)\n"
+	emit "PEEK = None\n"
+	emit "LINE = 1\n"
+	emit "\n"
+	emit "def peek():\n"
+	emit "    global PEEK\n"
+	emit "    if PEEK is None:\n"
+	emit "        char = sys.stdin.read(1)\n"
+	emit "        trace('char', char)\n"
+	emit "        if not char:\n"
+	emit "            PEEK = eof\n"
+	emit "        else:\n"
+	emit "            PEEK = char\n"
+	emit "    return PEEK\n"
+	emit "\n"
+	emit "def skip():\n"
+	emit "    global LINE\n"
+	emit "    global PEEK\n"
+	emit "    if eol == PEEK:\n"
+	emit "        LINE += 1\n"
+	emit "    PEEK = None\n"
+	emit "\n"
+	emit "def skipchar(char):\n"
+	emit "    global LINE\n"
+	emit "    assert char == peek(), (LINE, char, peek())\n"
+	emit "    skip()\n"
+	emit "\n"
+/
+
+emitfooter:
+	emit "if __name__ == '__main__':\n"
+	emit "    main()\n"
+/
+
+main:
+	emitheader
+	forever
+		calc char peek
+		calc iseof eq char eof
+		if iseof
+			break
+		/
+		forever
+			calc char peek
+			calc iseol eq char eol
+			calc isnoteol not iseol
+			if isnoteol
+				break
+			/
+			skip
+		/
+		parsefunc
+	/
+	emitfooter
+/