def statement():
"""
Parses
statement = ident selector ":=" expression |
ident "(" [expression {"," expression}] ")" |
compoundStatement |
"if" expression "then" Statement ["else" Statement] |
"while" expression "do" Statement.
Generates code for the statement if no error is reported
"""
if SC.sym not in FIRSTSTATEMENT:
mark("statement expected")
getSym()
while SC.sym not in FIRSTSTATEMENT | STRONGSYMS | FOLLOWSTATEMENT:
getSym()
if SC.sym == IDENT:
x = find(SC.val)
getSym()
x = genVar(x)
if type(x) in {Var, Ref}:
x = selector(x)
if SC.sym == BECOMES:
getSym()
y = expression()
if x.tp == y.tp in {Bool, Int}:
# if type(x) == Var: x = genAssign(x, y)
if type(x) == Var:
print("x: ", x, "y: ", y)
x = genAssign2(x, y)
else:
mark("illegal assignment")
else:
mark("incompatible assignment")
elif SC.sym == EQ:
mark(":= expected")
getSym()
y = expression()
else:
mark(":= expected")
elif type(x) in {Proc, StdProc} and SC.sym == LPAREN:
getSym()
fp, i = x.par, 0 # list of formal parameters
if SC.sym in FIRSTEXPRESSION:
y = expression()
if i < len(fp):
if type(fp[i]) == Var or type(y) == Var: # fp[i] == Ref and ty
if type(x) == Proc:
genActualPara(y, fp[i], i)
i = i + 1
else:
mark("illegal parameter mode")
else:
mark("extra parameter")
while SC.sym == COMMA:
getSym()
y = expression()
if i < len(fp):
if type(fp[i]) == Var or type(y) == Var:
if type(x) == Proc:
genActualPara(y, fp[i], i)
i = i + 1
else:
mark("illegal parameter mode")
else:
mark("extra parameter")
if i < len(fp):
mark("too few parameters")
if SC.sym == RPAREN:
getSym()
else:
mark("')' expected")
if type(x) == StdProc:
if x.name == "read":
x = genRead(y)
elif x.name == "write":
x = genWrite(y)
elif x.name == "writeln":
x = genWriteln()
else:
x = genCall(x)
else:
mark("variable or procedure expected")
elif SC.sym == BEGIN:
x = compoundStatement()
elif SC.sym == IF:
getSym()
x = expression()
if x.tp == Bool:
x = genCond(x)
else:
mark("boolean expected")
if SC.sym == THEN:
getSym()
else:
mark("'then' expected")
y = statement()
if SC.sym == ELSE:
y = genThen(x, y)
getSym()
z = statement()
x = genIfElse(x, y, z)
else:
x = genIfThen(x, y)
elif SC.sym == WHILE:
getSym()
t = genTarget()
x = expression()
if x.tp == Bool:
x = genCond(x)
else:
mark("boolean expected")
if SC.sym == DO:
getSym()
else:
mark("'do' expected")
y = statement()
x = genWhile(t, x, y)
else:
mark("invalid statement")
x = None
return x
elif x.name == 'write': x = genWrite(y)
elif x.name == 'writeln': x = genWriteln()
else: x = genCall(x)
else: mark("variable or procedure expected")
elif SC.sym == BEGIN: x = compoundStatement()
elif SC.sym == IF:
getSym(); x = expression(); q=1;
if x.tp == Bool: x = genCond(x)
elif x.tp == Int: q = 0 # if we skipped genrelation, prepare to skip following statement
else: mark('boolean expected')
if SC.sym == THEN: getSym()
else: mark("'then' expected")
if q=1: y = statement() # if (FALSE (q=0)) skip
if SC.sym == ELSE and q=1: # if (TRUE (q=1)) then perform THEN
y = genThen(x, y); getSym(); z = statement();
x = genIfElse(x, y, z)
else: x = genIfThen(x, y)
elif SC.sym == WHILE:
getSym(); t = genTarget(); x = expression()
if x.tp == Bool: x = genCond(x)
else: mark('boolean expected')
if SC.sym == DO: getSym()
else: mark("'do' expected")
y = statement(); x = genWhile(t, x, y)
else:
mark('invalid statement'); x = None
return x
#===============================================
def typ():
"""