diff --git a/README.markdown b/README.markdown
index 481183e..dcda79b 100644
--- a/README.markdown
+++ b/README.markdown
@@ -221,6 +221,22 @@
+ ignored
= (whatever stuff)
+And note that variables are subject to backtracking, too; if a variable is
+set while parsing something that failed, it is no longer set in the `|`
+alternative.
+
+ | main = set E = original &
+ | (set E = changed && "0" && "1" | "0" && "2") &
+ | return E.
+ + 0 1
+ = changed
+
+ | main = set E = original &
+ | (set E = changed && "0" && "1" | "0" && "2") &
+ | return E.
+ + 0 2
+ = original
+
The rule `fail` always fails. This lets you establish global flags, of
a sort.
diff --git a/eg/backtrack.tamsin b/eg/backtrack.tamsin
new file mode 100644
index 0000000..2db2fd5
--- /dev/null
+++ b/eg/backtrack.tamsin
@@ -0,0 +1,3 @@
+main = set E = original &
+ (set E = changed && "0" && "1" | "0" && "2") &
+ return E.
diff --git a/eg/bitpair.tamsin b/eg/bitpair.tamsin
new file mode 100644
index 0000000..b611870
--- /dev/null
+++ b/eg/bitpair.tamsin
@@ -0,0 +1,3 @@
+main = bit → A & bit → B & return (A B).
+bit = "0" | "1".
+
diff --git a/src/tamsin.py b/src/tamsin.py
index 2f03cdb..b4fa048 100755
--- a/src/tamsin.py
+++ b/src/tamsin.py
@@ -30,8 +30,11 @@
return result
def error(self, expected):
+ report = self.buffer[:20]
+ if len(self.buffer) > 20:
+ report += '...'
raise ValueError("Expected %s, found '%s' at '%s...'" %
- (expected, self.token, self.buffer[:20]))
+ (expected, self.token, report))
def scan(self):
self.scan_impl()
@@ -186,7 +189,44 @@
self.input = input_.split(' ')
self.position = 0
self.scan()
+ self.contexts = []
#print repr(self.input)
+
+ ### context stuff ---------------------------------------- ###
+
+ def push_context(self, purpose):
+ debug("pushing new context for %r" % purpose)
+ self.contexts.append({})
+
+ def pop_context(self, purpose):
+ debug("popping context for %r" % purpose)
+ self.contexts.pop()
+
+ def current_context(self):
+ """Don't assume anything about what this returns except that
+ you can pass it to install_context().
+
+ """
+ debug("retrieving current context %r" % self.contexts[-1])
+ return self.contexts[-1].copy()
+
+ def install_context(self, context):
+ debug("installing context %r" % context)
+ self.contexts[-1] = context
+
+ def fetch(self, name):
+ debug("fetching %s (it's %r)" %
+ (name, self.contexts[-1].get(name, 'undefined'))
+ )
+ return self.contexts[-1][name]
+
+ def store(self, name, value):
+ debug("updating %s (was %s) to %r" %
+ (name, self.contexts[-1].get(name, 'undefined'), value)
+ )
+ self.contexts[-1][name] = value
+
+ ### scanner stuff ---------------------------------------- ###
def scan(self):
if self.position >= len(self.input):
@@ -199,6 +239,8 @@
self.position = position
self.token = self.input[position - 1]
+ ### grammar stuff ---------------------------------------- ###
+
def find_production(self, name):
found = None
for x in self.program[1]:
@@ -209,15 +251,18 @@
raise ValueError("No '%s' production defined" % name)
return found
- def replace_vars(self, ast, context):
- """Expands a term."""
+ ### term stuff ---------------------------------------- ###
+
+ def replace_vars(self, ast):
+ """Expands a term, replacing all (VAR x) with the value of x
+ in the current context."""
if ast[0] == 'ATOM':
return ast
elif ast[0] == 'LIST':
- return ('LIST', [self.replace_vars(x, context) for x in ast[1]])
+ return ('LIST', [self.replace_vars(x) for x in ast[1]])
elif ast[0] == 'VAR':
- return context[ast[1]] # context.get(ast[1], None)
+ return self.fetch(ast[1])
else:
raise NotImplementedError("internal error: bad term")
@@ -231,58 +276,56 @@
else:
raise NotImplementedError("internal error: bad term")
- def interpret(self, ast, context):
+ ### interpreter proper ---------------------------------- ###
+
+ def interpret(self, ast):
if ast[0] == 'PROGRAM':
- return self.interpret(self.find_production('main'), context)
+ return self.interpret(self.find_production('main'))
elif ast[0] == 'PROD':
#print "interpreting %s" % repr(ast)
- return self.interpret(ast[2], {})
+ self.push_context(ast[1])
+ x = self.interpret(ast[2])
+ self.pop_context(ast[1])
+ return x
elif ast[0] == 'CALL':
- new_context = {}
- result = self.interpret(self.find_production(ast[1]), new_context)
+ result = self.interpret(self.find_production(ast[1]))
if ast[2] is not None:
assert ast[2][0] == 'VAR', ast
varname = ast[2][1]
- debug("updating %s (was %s) to %r" %
- (varname, context.get(varname, 'undefined'), result)
- )
- context[varname] = result
+ self.store(varname, result)
return result
elif ast[0] == 'SET':
assert ast[1][0] == 'VAR', ast
varname = ast[1][1]
- result = self.replace_vars(ast[2], context)
- debug("setting %s (was %s) to %r" %
- (varname, context.get(varname, 'undefined'), result)
- )
- context[varname] = result
+ result = self.replace_vars(ast[2])
+ self.store(varname, result)
return result
elif ast[0] == 'AND':
lhs = ast[1]
rhs = ast[2]
- value_lhs = self.interpret(lhs, context)
- value_rhs = self.interpret(rhs, context)
+ value_lhs = self.interpret(lhs)
+ value_rhs = self.interpret(rhs)
return value_rhs
elif ast[0] == 'OR':
lhs = ast[1]
rhs = ast[2]
- saved_context = context.copy()
+ saved_context = self.current_context()
saved_position = self.position
try:
- return self.interpret(lhs, context)
+ return self.interpret(lhs)
except TamsinParseError as e:
- context = saved_context
+ self.install_context(saved_context)
self.rewind(saved_position)
- return self.interpret(rhs, context)
+ return self.interpret(rhs)
elif ast[0] == 'RETURN':
- return self.replace_vars(ast[1], context)
+ return self.replace_vars(ast[1])
elif ast[0] == 'FAIL':
raise TamsinParseError("fail")
elif ast[0] == 'WHILE':
result = ('ATOM', 'nil')
while True:
try:
- result = self.interpret(ast[1], context)
+ result = self.interpret(ast[1])
except TamsinParseError as e:
return result
elif ast[0] == 'LITERAL':
@@ -297,21 +340,29 @@
raise NotImplementedError(repr(ast))
-if __name__ == '__main__':
- if sys.argv[1] == 'parse':
- with codecs.open(sys.argv[2], 'r', 'UTF-8') as f:
+def main(args):
+ global DEBUG
+ if args[0] == '--debug':
+ DEBUG = True
+ args = args[1:]
+ if args[0] == 'parse':
+ with codecs.open(args[1], 'r', 'UTF-8') as f:
contents = f.read()
parser = Parser(contents)
ast = parser.grammar()
print repr(ast)
- elif sys.argv[1] == 'run':
- with codecs.open(sys.argv[2], 'r', 'UTF-8') as f:
+ elif args[0] == 'run':
+ with codecs.open(args[1], 'r', 'UTF-8') as f:
contents = f.read()
parser = Parser(contents)
ast = parser.grammar()
#print repr(ast)
interpreter = Interpreter(ast, sys.stdin.read())
- result = interpreter.interpret(ast, {})
+ result = interpreter.interpret(ast)
print interpreter.stringify_term(result)
else:
raise ValueError("first argument must be 'parse' or 'run'")
+
+
+if __name__ == '__main__':
+ main(sys.argv[1:])
diff --git a/test.sh b/test.sh
index 61eaf40..c3fd733 100755
--- a/test.sh
+++ b/test.sh
@@ -1,3 +1,3 @@
#!/bin/sh
-falderal --substring-error README.md
+falderal --substring-error README.markdown