def selector(x):
while SC.sym in {PERIOD, LBRAK}:
if SC.sym == PERIOD: # x.f
getSym()
if SC.sym == IDENT:
if type(x.tp) == Record:
for f in x.tp.fields:
if f.name == SC.val:
x = CG.genSelect(x, f)
break
else:
mark("not a field")
getSym()
else:
mark("not a record")
else:
mark("identifier expected")
else: # x[y]
getSym()
y = expression()
if type(x.tp) == Array:
if y.tp == Int:
if type(y) == Const and \
(y.val < x.tp.lower or y.val >= x.tp.lower + x.tp.length):
mark('index out of bounds')
else:
x = CG.genIndex(x, y)
else:
mark('index not integer')
else:
mark('not an array')
if SC.sym == RBRAK: getSym()
else: mark("] expected")
return x
def term():
x = factor()
while SC.sym in {TIMES, DIV, MOD, AND}:
op = SC.sym
getSym()
if op == AND and type(x) != Const: x = CG.genUnaryOp(AND, x)
y = factor() # x op y
if x.tp == Int == y.tp and op in {TIMES, DIV, MOD}:
if type(x) == Const == type(y): # constant folding
if op == TIMES: x.val = x.val * y.val
elif op == DIV: x.val = x.val // y.val
elif op == MOD: x.val = x.val % y.val
else: x = CG.genBinaryOp(op, x, y)
elif x.tp == Bool == y.tp and op == AND:
if type(x) == Const: # constant folding
if x.val: x = y # if x is true, take y, else x
else: x = CG.genBinaryOp(AND, x, y)
else: mark('bad type')
return x
def expression():
x = simpleExpression()
while SC.sym in {EQ, NE, LT, LE, GT, GE}:
op = SC.sym
getSym()
y = simpleExpression() # x op y
if x.tp == y.tp in (Int, Bool):
if type(x) == Const == type(y): # constant folding
if op == EQ: x.val = x.val == y.val
elif op == NE: x.val = x.val != y.val
elif op == LT: x.val = x.val < y.val
elif op == LE: x.val = x.val <= y.val
elif op == GT: x.val = x.val > y.val
elif op == GE: x.val = x.val >= y.val
x.tp = Bool
else:
x = CG.genRelation(op, x, y)
else:
mark('bad type')
return x
def simpleExpression():
if SC.sym == PLUS:
getSym()
x = term()
elif SC.sym == MINUS:
getSym()
x = term()
if x.tp != Int: mark('bad type')
elif type(x) == Const: x.val = -x.val # constant folding
else: x = CG.genUnaryOp(MINUS, x)
else: x = term()
while SC.sym in {PLUS, MINUS, OR}:
op = SC.sym
getSym()
if op == OR and type(x) != Const: x = CG.genUnaryOp(OR, x)
y = term() # x op y
if x.tp == Int == y.tp and op in {PLUS, MINUS}:
if type(x) == Const == type(y): # constant folding
if op == PLUS: x.val = x.val + y.val
elif op == MINUS: x.val = x.val - y.val
else: x = CG.genBinaryOp(op, x, y)
elif x.tp == Bool == y.tp and op == OR:
if type(x) == Const: # constant folding
if not x.val: x = y # if x is false, take y, else x
else: x = CG.genBinaryOp(OR, x, y)
else: mark('bad type')
return x
def compoundStatement():
if SC.sym == BEGIN: getSym()
else: mark("'begin' expected")
x = statement()
while SC.sym == SEMICOLON or SC.sym in FIRSTSTATEMENT:
if SC.sym == SEMICOLON: getSym()
else: mark("; missing")
y = statement()
x = CG.genSeq(x, y)
if SC.sym == END: getSym()
else: mark("'end' expected")
return x
def typedIds(kind):
if SC.sym == IDENT:
tid = [SC.val]
getSym()
else:
mark("identifier expected")
tid = []
while SC.sym == COMMA:
getSym()
if SC.sym == IDENT:
tid.append(SC.val)
getSym()
else:
mark('identifier expected')
if SC.sym == COLON:
getSym()
tp = typ().val
if tp != None:
for i in tid:
newDecl(i, kind(tp))
else:
mark("':' expected")
def program():
newDecl('boolean', Type(CG.genBool(Bool)))
newDecl('integer', Type(CG.genInt(Int)))
newDecl('true', Const(Bool, 1))
newDecl('false', Const(Bool, 0))
newDecl('read', StdProc([Ref(Int)]))
newDecl('write', StdProc([Var(Int)]))
newDecl('writeln', StdProc([]))
newDecl('print', StdProc([Var(Int)]))
CG.genProgStart()
if SC.sym == PROGRAM: getSym()
else: mark("'program' expected")
ident = SC.val
if SC.sym == IDENT: getSym()
else: mark('program name expected')
if SC.sym == SEMICOLON: getSym()
else: mark('; expected')
declarations(CG.genGlobalVars)
CG.genProgEntry(ident)
x = compoundStatement()
return CG.genProgExit(x)
def factor():
if SC.sym not in FIRSTFACTOR:
mark("expression expected")
while SC.sym not in FIRSTFACTOR | FOLLOWFACTOR | STRONGSYMS:
getSym()
if SC.sym == IDENT:
x = find(SC.val)
if type(x) in {Var, Ref}:
x = CG.genVar(x)
getSym()
elif type(x) == Const:
x = Const(x.tp, x.val)
x = CG.genConst(x)
getSym()
else:
mark('expression expected')
x = selector(x)
elif SC.sym == NUMBER:
x = Const(Int, SC.val)
x = CG.genConst(x)
getSym()
elif SC.sym == LPAREN:
getSym()
x = expression()
if SC.sym == RPAREN: getSym()
else: mark(") expected")
elif SC.sym == NOT:
getSym()
x = factor()
if x.tp != Bool: mark('not boolean')
elif type(x) == Const: x.val = 1 - x.val # constant folding
else: x = CG.genUnaryOp(NOT, x)
else: x = Const(None, 0)
return x
def declarations(allocVar):
if SC.sym not in FIRSTDECL | FOLLOWDECL:
mark("'begin' or declaration expected")
while SC.sym not in FIRSTDECL | FOLLOWDECL | STRONGSYMS:
getSym()
while SC.sym == CONST:
getSym()
if SC.sym == IDENT:
ident = SC.val
getSym()
if SC.sym == EQ: getSym()
else: mark("= expected")
x = expression()
if type(x) == Const: newDecl(ident, x)
else: mark('expression not constant')
else: mark("constant name expected")
if SC.sym == SEMICOLON: getSym()
else: mark("; expected")
while SC.sym == TYPE:
getSym()
if SC.sym == IDENT:
ident = SC.val
getSym()
if SC.sym == EQ: getSym()
else: mark("= expected")
x = typ()
newDecl(ident, x) # x is of type ST.Type
if SC.sym == SEMICOLON: getSym()
else: mark("; expected")
else: mark("type name expected")
start = len(topScope())
while SC.sym == VAR:
getSym()
typedIds(Var)
if SC.sym == SEMICOLON: getSym()
else: mark("; expected")
varsize = allocVar(topScope(), start)
while SC.sym == PROCEDURE:
getSym()
if SC.sym == IDENT: getSym()
else: mark("procedure name expected")
ident = SC.val
newDecl(ident, Proc([])) # entered without parameters
sc = topScope()
openScope() # new scope for parameters and body
if SC.sym == LPAREN:
getSym()
if SC.sym in {VAR, IDENT}:
if SC.sym == VAR:
getSym()
typedIds(Ref)
else:
typedIds(Var)
while SC.sym == SEMICOLON:
getSym()
if SC.sym == VAR:
getSym()
typedIds(Ref)
else:
typedIds(Var)
else:
mark("formal parameters expected")
fp = topScope()
sc[-1].par = fp[:] # procedure parameters updated
if SC.sym == RPAREN: getSym()
else: mark(") expected")
else: fp = []
parsize = CG.genProcStart(ident, fp)
if SC.sym == SEMICOLON: getSym()
else: mark("; expected")
localsize = declarations(CG.genLocalVars)
CG.genProcEntry(ident, parsize, localsize)
x = compoundStatement()
CG.genProcExit(x, parsize, localsize)
closeScope() # scope for parameters and body closed
if SC.sym == SEMICOLON: getSym()
else: mark("; expected")
return varsize
def typ():
if SC.sym not in FIRSTTYPE:
mark("type expected")
while SC.sym not in FIRSTTYPE | FOLLOWTYPE | STRONGSYMS:
getSym()
if SC.sym == IDENT:
ident = SC.val
x = find(ident)
getSym()
if type(x) == Type: x = Type(x.val)
else:
mark('not a type')
x = Type(None)
elif SC.sym == ARRAY:
getSym()
if SC.sym == LBRAK: getSym()
else: mark("'[' expected")
x = expression()
if SC.sym == PERIOD: getSym()
else: mark("'.' expected")
if SC.sym == PERIOD: getSym()
else: mark("'.' expected")
y = expression()
if SC.sym == RBRAK: getSym()
else: mark("']' expected")
if SC.sym == OF: getSym()
else: mark("'of' expected")
z = typ().val
if type(x) != Const or x.val < 0:
mark('bad lower bound')
x = Type(None)
elif type(y) != Const or y.val < x.val:
mark('bad upper bound')
x = Type(None)
else:
x = Type(CG.genArray(Array(z, x.val, y.val - x.val + 1)))
elif SC.sym == RECORD:
getSym()
openScope()
typedIds(Var)
while SC.sym == SEMICOLON:
getSym()
typedIds(Var)
if SC.sym == END: getSym()
else: mark("'end' expected")
r = topScope()
closeScope()
x = Type(CG.genRec(Record(r)))
else:
x = Type(None)
return x
def statement():
if SC.sym not in FIRSTSTATEMENT:
mark("statement expected")
getSym()
while SC.sym not in FIRSTSTATEMENT | FOLLOWSTATEMENT | STRONGSYMS:
getSym()
if SC.sym == IDENT:
x = find(SC.val)
getSym()
if type(x) in {Var, Ref}:
x = CG.genVar(x)
x = selector(x)
if SC.sym == BECOMES:
getSym()
y = expression()
if x.tp == y.tp in {Bool, Int}: x = CG.genAssign(x, y)
else: mark('incompatible assignment')
elif SC.sym == EQ:
mark(':= expected')
getSym()
y = expression()
else:
mark(':= expected')
elif type(x) in {Proc, StdProc}:
fp, ap, i = x.par, [], 0 # list of formals, list of actuals
if SC.sym == LPAREN:
getSym()
if SC.sym in FIRSTEXPRESSION:
y = expression()
if i < len(fp):
if (type(fp[i]) == Var or type(y) == Var) and \
fp[i].tp == y.tp:
if type(x) == Proc:
ap.append(CG.genActualPara(y, fp[i], i))
else:
mark('illegal parameter mode')
else:
mark('extra parameter')
i = i + 1
while SC.sym == COMMA:
getSym()
y = expression()
if i < len(fp):
if (type(fp[i]) == Var or type(y) == Var) and \
fp[i].tp == y.tp:
if type(x) == Proc:
ap.append(CG.genActualPara(y, fp[i], i))
else:
mark('illegal parameter mode')
else:
mark('extra parameter')
i = i + 1
if SC.sym == RPAREN: getSym()
else: mark("')' expected")
if i < len(fp): mark('too few parameters')
elif type(x) == StdProc:
if x.name == 'read': x = CG.genRead(y)
elif x.name == 'write': x = CG.genWrite(y)
elif x.name == 'writeln': x = CG.genWriteln()
elif x.name == 'print': x = CG.genPrint(y)
else: x = CG.genCall(x, ap)
else: mark("variable or procedure expected")
elif SC.sym == BEGIN: x = compoundStatement()
elif SC.sym == IF:
getSym()
x = expression()
if x.tp == Bool: x = CG.genThen(x)
else: mark('boolean expected')
if SC.sym == THEN: getSym()
else: mark("'then' expected")
y = statement()
if SC.sym == ELSE:
if x.tp == Bool: y = CG.genElse(x, y)
getSym()
z = statement()
if x.tp == Bool: x = CG.genIfElse(x, y, z)
else:
if x.tp == Bool: x = CG.genIfThen(x, y)
elif SC.sym == WHILE:
getSym()
t = CG.genWhile()
x = expression()
if x.tp == Bool: x = CG.genDo(x)
else: mark('boolean expected')
if SC.sym == DO: getSym()
else: mark("'do' expected")
y = statement()
if x.tp == Bool: x = CG.genWhileDo(t, x, y)
else: x = None
return x