If

README.md

@@ -16,9 +16,9 @@ Increments:
 - [X] Unary Operators on Ints
 - [X] Local Variables and Assignment
 - [X] Booleans 
-- [ ] Branching (if statements)
-- [ ] Comparisons
+- [X] Branching (if statements)
 - [ ] WriteLn("Hello World") (finally)
+- [ ] Comparisons
 - [ ] Loops
 - [ ] Procedures
 - [ ] Functions

src/HSPC/CodeGen.hs

@@ -56,6 +56,18 @@ generateBlock (MainProgramBlock vars body) =
         ++ [0x5d] -- pop rbp
 
 generateStatement :: OffsetMap -> Statement -> [Word8]
+generateStatement _ NOP = []
+generateStatement offsetMap (If cond statement elseStatement) =
+  let statementCode = generateStatement offsetMap statement
+      elseStatementCode = generateStatement offsetMap elseStatement
+   in generateExpression offsetMap cond
+        ++ [0x48, 0x85, 0xc0] -- test rax rax
+        ++ [0x0f, 0x84]
+        ++ int32ToLE (fromIntegral $ length statementCode + 5) -- jz elseStatement
+        ++ statementCode
+        ++ [0xe9]
+        ++ int32ToLE (fromIntegral $ length elseStatementCode) -- jz elseStatementCode
+        ++ elseStatementCode
 generateStatement offsetMap (Halt ast) =
   generateExpression offsetMap ast
     -- copy rax -> rdi but maxed out at 255

src/HSPC/Parse.hs

@@ -28,6 +28,9 @@ data Block
 
 data Statement
   = VarAssign String Expression
+  | -- if Expression then Statement else Statement;
+    If Expression Statement Statement
+  | NOP
   | Assignment String Expression
   | Halt Expression
   | ExprStmt Expression
@@ -133,27 +136,47 @@ parseStatements :: Map.Map String HSPCDataType -> [Statement] -> [HSPCToken] ->
 parseStatements _ acc (EndKeyWordTok : xs) = Right (reverse acc, xs)
 parseStatements _ _ [] = Left ExpectedEndStatement
 parseStatements vars acc xs = do
-  (expr, rest) <- parseStatement vars xs
+  (expr, restWithSemiColon) <- parseStatement vars xs
+  rest <- removeLeadingSemiColon restWithSemiColon
   parseStatements vars (expr : acc) rest
 
 parseStatement :: Map.Map String HSPCDataType -> [HSPCToken] -> Either ParseError (Statement, [HSPCToken])
 parseStatement varMap (IdentifierTok name : AssignmentTok : xs) = do
-  let (rhs, rawRest) = break (== SemiColonTok) xs
-  rest <- removeLeadingSemiColon rawRest
+  let (rhs, rest) = break (`elem` [SemiColonTok, ElseKeyWordTok]) xs
   op <- case Map.lookup name varMap of
     Just dt -> parseOperand dt rhs
     Nothing -> Left $ VariableNotDeclared name
   return (Assignment name op, rest)
 parseStatement
   _
-  (HaltBuiltInTok : OpenBracketTok : CloseBracketTok : SemiColonTok : xs) = Right (Halt (IntLiteral 0), xs)
+  (HaltBuiltInTok : OpenBracketTok : CloseBracketTok : xs) = Right (Halt (IntLiteral 0), xs)
 parseStatement
   _
   (HaltBuiltInTok : OpenBracketTok : xs) = do
-    (internal, rawRest) <- splitToMatchingBracket xs
-    rest <- removeLeadingSemiColon rawRest
+    (internal, rest) <- splitToMatchingBracket xs
     op <- parseOperand IntegerType internal
     return (Halt op, rest)
+
+-- "IF cond THEN statement (; | ELSE elseStatement;)"
+-- ELSE IF is simply an if statement where elseSatement
+-- is another if statement.
+parseStatement varMap (IfKeyWordTok : xs) = do
+  (cond, afterThen) <- parseCond xs
+  (statement, afterStatement) <- parseStatement varMap afterThen
+  case afterStatement of
+    (SemiColonTok : outsideOfStatement) ->
+      return (If cond statement NOP, SemiColonTok : outsideOfStatement)
+    (ElseKeyWordTok : afterElse) -> do
+      (elseStatement, afterElseStatement) <- parseStatement varMap afterElse
+      outsideOfStatement <- removeLeadingSemiColon afterElseStatement
+      return (If cond statement elseStatement, SemiColonTok : outsideOfStatement)
+    _ -> Left $ ExpectedToken SemiColonTok
+  where
+    parseCond :: [HSPCToken] -> Either ParseError (Expression, [HSPCToken])
+    parseCond tokens = do
+      let (condTokens, afterCond) = break (== ThenKeyWordTok) tokens
+      cond <- parseOperand BooleanType condTokens
+      return (cond, drop 1 afterCond)
 parseStatement _ tok = Left $ NotImplemented "parseStatement" tok
 
 parseOperand :: HSPCDataType -> [HSPCToken] -> Either ParseError Expression
@@ -199,6 +222,7 @@ parseIntOperand tokens = case breakLastOuter (`elem` [PlusTok, MinusTok]) tokens
 
     parseFactor :: [HSPCToken] -> Either ParseError Expression
     parseFactor [LiteralIntTok n] = Right $ IntLiteral n
+    -- TODO: check that this variable exists
     parseFactor [IdentifierTok name] = Right $ Identifier name
     parseFactor (PlusTok : xs) = do
       operand <- parseFactor xs
@@ -246,6 +270,7 @@ parseBoolOperand tokens = case breakLastOuter (== OrTok) tokens of
 
     parseBoolPrimary :: [HSPCToken] -> Either ParseError Expression
     parseBoolPrimary [LiteralBoolTok bool] = Right $ BoolLiteral bool
+    parseBoolPrimary [IdentifierTok name] = Right $ Identifier name
     parseBoolPrimary (OpenBracketTok : xs) = do
       (inside, remaining) <- splitToMatchingBracket xs
       case remaining of

src/HSPC/Tokenize.hs

@@ -13,6 +13,9 @@ data HSPCToken
   | VarKeyWordTok
   | BeginKeyWordTok
   | EndKeyWordTok
+  | IfKeyWordTok
+  | ElseKeyWordTok
+  | ThenKeyWordTok
   | HaltBuiltInTok
   | OpenBracketTok
   | CloseBracketTok
@@ -49,6 +52,9 @@ tokenize (c : cs)
 tokenizeIdentifierOrKeyWord :: String -> HSPCToken
 tokenizeIdentifierOrKeyWord "PROGRAM" = ProgramKeyWordTok
 tokenizeIdentifierOrKeyWord "VAR" = VarKeyWordTok
+tokenizeIdentifierOrKeyWord "IF" = IfKeyWordTok
+tokenizeIdentifierOrKeyWord "ELSE" = ElseKeyWordTok
+tokenizeIdentifierOrKeyWord "THEN" = ThenKeyWordTok
 tokenizeIdentifierOrKeyWord "BEGIN" = BeginKeyWordTok
 tokenizeIdentifierOrKeyWord "HALT" = HaltBuiltInTok
 tokenizeIdentifierOrKeyWord "DIV" = IntDivideTok

test/Main.hs

@@ -39,7 +39,11 @@ testSuite =
     TestSpec "{} comments" "comments_curly_brace" 12,
     TestSpec "// comments" "comments_single_line" 12,
     TestSpec "Single variable" "variables_single_var" 10,
-    TestSpec "Boolean variable" "variables_bool" 0
+    TestSpec "Boolean variable" "variables_bool" 0,
+    TestSpec "IF" "if_no_else" 30,
+    TestSpec "IF ELSE" "if_else" 40,
+    TestSpec "IF ELSE IF" "if_else_if" 40,
+    TestSpec "IF with complex cond" "if_complex_cond" 40
   ]
 
 main :: IO ()

test/sample_programs/if_complex_cond.pas

@@ -0,0 +1,16 @@
+program IfExample;
+
+var 
+    i : integer;
+    b : boolean;
+begin
+    i := 10;
+    b := false;
+
+    if (b or False) then
+        i := 30
+    else if (True and (not b)) then
+        i := 40;
+
+    halt(i); 
+end.

test/sample_programs/if_else.pas

@@ -0,0 +1,14 @@
+program IfExample;
+
+var 
+    i : integer;
+begin
+    i := 10;
+
+    if (False) then
+        i := 30
+    else 
+        i := 40;
+
+    halt(i); 
+end.

test/sample_programs/if_else_if.pas

@@ -0,0 +1,14 @@
+program IfExample;
+
+var 
+    i : integer;
+begin
+    i := 10;
+
+    if (False) then
+        i := 30
+    else if (true) then
+        i := 40;
+
+    halt(i); 
+end.

test/sample_programs/if_no_else.pas

@@ -0,0 +1,12 @@
+program IfExample;
+
+var 
+    i : integer;
+begin
+    i := 10;
+
+    if (True) then
+        i := 30;
+
+    halt(i); 
+end.