Else if

src/main/antlr/SimpleLanguage.g4

@@ -12,7 +12,7 @@ statement
     | expression NEWLINE # expressionStmt
     | functionDefinition NEWLINE # functionDefinitionStmt
     | classDefinition NEWLINE # classDefinitionStmt
-    | IF LPAREN expression RPAREN thenBlock=block (ELSE elseBlock=block)? NEWLINE # ifStmt
+    | IF LPAREN ifExpression=expression RPAREN ifThenBlock=block (ELSE IF LPAREN elseIfExpression=expression RPAREN elseIfThenBlock=block)* (ELSE elseBlock=block)? NEWLINE # ifStmt
     | WHILE LPAREN expression RPAREN body=block NEWLINE # whileStmt
     | RETURN expression NEWLINE # returnStatement
     | NEWLINE # newlineStmt

src/main/kotlin/ast/AstNodes.kt

@@ -45,11 +45,13 @@ data class FunctionDeclarationStatement(
 }
 
 data class IfStatement(
-    val condition: Expression,
-    val thenBlock: Block,
+    val ifCondition: Expression,
+    val elseIfConditions: List<Expression>?,
+    val ifThenBlock: Block,
+    val elseIfThenBlocks: List<Block>?,
     val elseBlock: Block?
 ) : Statement {
-    override val children = listOfNotNull(condition, thenBlock, elseBlock)
+    override val children = listOfNotNull(ifCondition, ifThenBlock, elseBlock) + elseIfConditions.orEmpty() + elseIfThenBlocks.orEmpty()
 
     override fun <T> acceptVisitor(visitor: AstVisitor<T>): T = visitor.visitIfStatement(this)
 }

src/main/kotlin/codegen/dsl/ControlFlow.kt

@@ -3,12 +3,12 @@ package codegen.dsl
 import codegen.ChunkBuilder
 import codegen.Code
 
-fun ChunkBuilder.ifStatement(condition: Code, thenCode: Code, elseCode: Code = {}) {
+fun ChunkBuilder.ifStatement(ifCondition: Code, thenCode: Code, elseCode: Code = {}) {
     val afterThen = looseLabel("after then")
     val afterIf = looseLabel("after if")
 
     // IF
-    +condition // CONDITION
+    +ifCondition // CONDITION
     jumpForwardIfFalse(afterThen)
     // THEN
     pop() // pop CONDITION
@@ -23,6 +23,42 @@ fun ChunkBuilder.ifStatement(condition: Code, thenCode: Code, elseCode: Code = {
     putLabel(afterIf)
 }
 
+fun ChunkBuilder.ifStatement(ifConditions: List<Code>, thenCodes: List<Code>, elseCode: Code = {}) {
+    val afterAllThen = looseLabel("after then")
+    val afterAllIf = looseLabel("after all if")
+    val afterIf = mutableListOf<ChunkBuilder.Label>()
+
+    for ((index, condition) in ifConditions.withIndex()) {
+        afterIf.add(looseLabel("after $index if"))
+    }
+
+    var currentAfterCondition: ChunkBuilder.Label? = null
+
+    for ((index, condition) in ifConditions.withIndex()) {
+        currentAfterCondition = looseLabel("after $index")
+        +condition
+        jumpForwardIfFalse(afterIf[index])
+        pop()
+        +thenCodes[index]
+        jumpTo(afterAllIf)
+        putLabel(afterIf[index])
+    }
+
+//    +ifCondition
+//    jumpForwardIfFalse(afterAllThen)
+//
+//    pop()
+//    +thenCode
+//
+//    jumpTo(afterIf)
+
+    putLabel(afterAllThen)
+    pop()
+    +elseCode
+
+    putLabel(afterAllIf)
+}
+
 fun ChunkBuilder.whileLoop(condition: Code, body: Code) {
     val beforeLoop = looseLabel("before loop")
     val afterBody = looseLabel("after body")

src/main/kotlin/compiler/Compiler.kt

@@ -8,6 +8,7 @@ import codegen.instructions.SetFieldInstruction
 import resolve.*
 import stdlib.BuiltInFunction
 import stdlib.addBuiltInFunction
+import java.util.concurrent.locks.Condition
 
 fun compile(
     builtInFunctions: List<BuiltInFunction>,
@@ -116,10 +117,28 @@ private class CompilerVisitor(builtInFunctions: List<BuiltInFunction>, private v
     }
 
     override fun visitIfStatement(ifStatement: IfStatement): Code = {
-        val condition = visit(ifStatement.condition)
-        val thenCode = visit(ifStatement.thenBlock)
+        val ifCondition = visit(ifStatement.ifCondition)
+        val elseIfConditions = ifStatement.elseIfConditions?.map { visit(it) }
+        val ifThenCode = visit(ifStatement.ifThenBlock)
+        val elseIfThenCodes = ifStatement.elseIfThenBlocks?.map { visit(it) }
         val elseCode = ifStatement.elseBlock?.let { visit(it) } ?: {}
-        ifStatement(condition, thenCode, elseCode)
+
+        val conditions: MutableList<Code>
+        if (elseIfConditions != null) {
+            conditions = elseIfConditions.toMutableList()
+            conditions.add(0, ifCondition)
+        } else {
+            conditions = mutableListOf(ifCondition)
+        }
+
+        val thenCodes: MutableList<Code>
+        if (elseIfThenCodes != null) {
+            thenCodes = elseIfThenCodes.toMutableList()
+            thenCodes.add(0, ifThenCode)
+        } else {
+            thenCodes = mutableListOf(ifThenCode)
+        }
+        ifStatement(conditions, thenCodes, elseCode)
     }
 
     override fun visitWhileStatement(whileStatement: WhileStatement): Code = {

src/main/kotlin/parsing/AstBuilder.kt

@@ -40,10 +40,20 @@ class AstBuilder : SimpleLanguageBaseVisitor<AstNode?>() {
     }
 
     override fun visitIfStmt(ctx: SimpleLanguageParser.IfStmtContext?): IfStatement {
-        val condition = visit(ctx!!.expression()) as Expression
-        val thenBlock = visitBlock(ctx.thenBlock)
+//        val condition = visit(ctx!!.expression()) as Expression
+//        val thenBlock = visitBlock(ctx.thenBlock)
+//        val elseBlock = ctx.elseBlock?.let { visitBlock(it) }
+//        return IfStatement(condition, thenBlock, elseBlock)
+
+        val ifCondition = visit(ctx!!.ifExpression) as Expression
+        val elseIfConditionContexts = ctx.expression().drop(1)
+        val elseIfConditions = elseIfConditionContexts.map { visit(it) as Expression }
+        val ifThenBlock = visitBlock(ctx.ifThenBlock)
+        val elseIfThenBlockContexts = ctx.block().drop(1)
+        val elseIfThenBlocks = elseIfThenBlockContexts.map { visitBlock(it) }
         val elseBlock = ctx.elseBlock?.let { visitBlock(it) }
-        return IfStatement(condition, thenBlock, elseBlock)
+
+        return IfStatement(ifCondition, elseIfConditions, ifThenBlock, elseIfThenBlocks, elseBlock)
     }
 
     override fun visitWhileStmt(ctx: SimpleLanguageParser.WhileStmtContext?): AstNode {

src/main/kotlin/stdlib/BuiltInFunctions.kt

@@ -25,7 +25,7 @@ object FactFunction : BuiltInFunction {
     override val arity: Int = 1
     override val code: Code = {
         ifStatement(
-            condition = {
+            ifCondition = {
                 equal({ getLocalVariable(1) }, { literal(1) })
             },
             thenCode = {