diff --git a/debugger/steps.coffee b/debugger/steps.coffee
new file mode 100644
index 0000000..3141457
--- /dev/null
+++ b/debugger/steps.coffee
@@ -0,0 +1,34 @@
+{ instructionQueue } = require '../interpreter/vm-state'
+Ast = require '../parser/ast'
+{ getFunctionMap } = require '../interpreter/function'
+
+{ NODES, STATEMENTS, OPERATORS } = Ast
+
+@stepOut = ->
+  i = instructionQueue.length - 1
+  while i >= 0
+    break if instructionQueue[i].getType() is NODES.END_FUNC_BLOCK
+    --i
+  instructionQueue[--i].stop = yes
+
+@stepOver = ->
+  i = instructionQueue.length - 1
+  while i >= 0
+    if instructionQueue[i].getType() is NODES.FUNCALL
+      instructionQueue[i].stop = yes
+      break
+    if instructionQueue[i].getType() is NODES.END_FUNC_BLOCK and i > 0
+      instructionQueue[--i].stop = yes
+      break
+    --i
+
+@stepInto = ->
+  instr = instructionQueue[instructionQueue.length - 1]
+  if instr.getType() is NODES.FUNCALL
+    { instructions } = getFunctionMap()[instr.getChild(0).getChild(0)]
+    console.log instructions
+    instructions.getChild(0).stop = yes
+  else
+    instr.stop = yes
+
+module.exports = @
diff --git a/gulpfile.js b/gulpfile.js
index edf9f3e..64e9cd5 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -23,7 +23,7 @@ gulp.task('dev', function() {
         .transform(coffeeify)
         .transform(jisonify)
         .bundle()
-        .pipe(source('index.js'))
+        .pipe(source('index.min.js'))
         .pipe(gulp.dest('./lib'))
 });
 
diff --git a/index.coffee b/index.coffee
index 7ef9187..3dd32e7 100644
--- a/index.coffee
+++ b/index.coffee
@@ -2,6 +2,9 @@
 { checkSemantics } = require './semantics/'
 interpreter = require './interpreter/'
 Ast = require './parser/ast.coffee'
+io = require './interpreter/io'
+Stack = require './interpreter/stack'
+{ stepInto, stepOver, stepOut } = require './debugger/steps'
 
 parser.yy = { Ast }
 
@@ -18,14 +21,25 @@ parser.yy = { Ast }
 
     loop
       { value, done } = iterator.next()
-      yield value
       break unless not done
-      result = value
-    yield result
+      yield value: value, stack: Stack.stack
+    yield 0
+
+@hooks = {
+    setInput: (input) -> io.setInput(io.STDIN, input)
+    isInputBufferEmpty: -> io.isInputBufferEmpty(io.STDIN)
+    modifyVariable: (stackNumber, varName, value) -> Stack.stack[stackNumber].variables[varName].value = value
+}
 
 @events = {
     onstdout: (cb) -> interpreter.onstdout cb
 }
 
+@actions = {
+    stepOut: -> stepOut()
+    stepOver: -> stepOver()
+    stepInto: -> stepInto()
+}
+
 
 self.cmm = @
diff --git a/interpreter/function.coffee b/interpreter/function.coffee
index 704a211..21e4456 100644
--- a/interpreter/function.coffee
+++ b/interpreter/function.coffee
@@ -4,14 +4,17 @@ Stack = require './stack'
 Ast = require '../parser/ast'
 Error = require '../error'
 Expression = require './expression'
+{ instructionQueue } = require './vm-state'
+
 
 { NODES, TYPES } = Ast
 
 module.exports = @
 
-# Of the form: { <funcId>: { type: tipus, argIds: [id1, id2, ..., idn] } }
+# Of the form: { <funcId>: { type: tipus, argTypes: [ty1, ty2, ..., tyn] argIds: [id1, id2, ..., idn], instructions: instruccions } }
 functions = null
 
+@getFunctionMap = -> functions
 
 @mapFunctions = (T) ->
     functions = {}
@@ -19,9 +22,10 @@ functions = null
     for functionTree in T.getChildren()
         assert.strictEqual functionTree.getType(), TYPES.FUNCTION
         funcId = functionTree.getChild(1).getChild(0)
+        argTypes = (argAst.getChild(0) for argAst in functionTree.getChild(2).getChildren())
         argIds = (argAst.getChild(1).getChild(0) for argAst in functionTree.getChild(2).getChildren())
         type = functionTree.getChild(0)
-        functions[funcId] = { type, argIds, instructions: functionTree.getChild(3) }
+        functions[funcId] = { type, argTypes, argIds, instructions: functionTree.getChild(3) }
     return
 
 @initFunction = (T) ->
@@ -34,23 +38,28 @@ functions = null
 
     assert func?, 'Function ' + funcId + ' not declared'
 
-    { type, argIds, instructions } = func
+    { type, argTypes, argIds, instructions } = func
 
     assert argIds.length is argValuesAst.getChildCount()
 
     argIdValuePairs =
         for id, i in argIds
+            type: argTypes[i]
             id: id
             value: Expression.evaluateExpression(argValuesAst.getChild(i))
 
     result = null
 
-    Stack.pushActivationRecord()
+    Stack.pushActivationRecord(funcId, argIds)
 
-    for { id, value } in argIdValuePairs
-        Stack.defineVariable id, value
+    for { type, id, value } in argIdValuePairs
+        Stack.defineVariable id, type, value, param=yes
 
-    instructions
+    instructionQueue.push new Ast NODES.END_FUNC_BLOCK, []
+    instructionQueue.push instructions
 
 @finalizeFunction = ->
+    loop
+      instr = instructionQueue.pop()
+      break if instr.getType() is NODES.END_FUNC_BLOCK
     Stack.popActivationRecord()
diff --git a/interpreter/index.coffee b/interpreter/index.coffee
index 7470c4b..92156c2 100644
--- a/interpreter/index.coffee
+++ b/interpreter/index.coffee
@@ -3,7 +3,7 @@ assert = require 'assert'
 Error = require '../error'
 Ast = require '../parser/ast'
 Stack = require './stack'
-{ mapFunctions, initFunction, finalizeFunction } = require './function'
+{ mapFunctions, initFunction } = require './function'
 { initRunner, executeInstruction } = require './runner'
 io = require './io'
 
@@ -19,20 +19,14 @@ module.exports = @
     io.reset()
     io.setInput(io.STDIN, input)
 
-    try
-        instructions = initFunction new Ast(NODES.FUNCALL, [new Ast(NODES.ID, ["main"]), new Ast(NODES.PARAM_LIST, [])])
-        initRunner instructions
-        iterator = executeInstruction()
-        loop
-          { value, done } = iterator.next()
-          yield value
-          break unless not done
-          status = value
-        finalizeFunction()
-    catch error
-        console.error error.stack ? error.message ? error
-        io.output io.STDERR, error.message
-        status = error.code
+    initFunction new Ast(NODES.FUNCALL, [new Ast(NODES.ID, ["main"]), new Ast(NODES.PARAM_LIST, [])])
+    initRunner()
+    iterator = executeInstruction()
+    loop
+      { value, done } = iterator.next()
+      break unless not done
+      yield value
+      status = value
 
     yield { status, stderr: io.getStream(io.STDERR) }
 
diff --git a/interpreter/io.coffee b/interpreter/io.coffee
index 4c09ee3..b87cadf 100644
--- a/interpreter/io.coffee
+++ b/interpreter/io.coffee
@@ -27,6 +27,7 @@ module.exports = class IO
 
         IO.streams[stream] += string
         IO.stdoutCB IO.streams[IO.STDOUT]
+        IO.streams[IO.STDOUT] = '';
 
     @setInput: (stream, input) ->
         assert (typeof input is "string")
@@ -48,3 +49,5 @@ module.exports = class IO
     @getStream: (stream) -> IO.streams[stream]
 
     @setStdoutCB: (cb) -> IO.stdoutCB = cb
+
+    @isInputBufferEmpty: (stream) -> IO.streams[stream].length is 0
diff --git a/interpreter/runner.coffee b/interpreter/runner.coffee
index 48afcd8..4724bac 100644
--- a/interpreter/runner.coffee
+++ b/interpreter/runner.coffee
@@ -13,9 +13,7 @@ io = require './io'
 
 module.exports = @
 
-@initRunner = (T) ->
-    @root = T
-    instructionQueue = [T]
+@initRunner = ->
     @openScopes = {}
 
 @getNumberInstructions = ->
@@ -35,14 +33,15 @@ executeInstructionHelper = (T) ->
             unwrapBlock T
         when NODES.DECLARATION
             declarations = T.getChild 1
+            type = T.getChild 0
             for declaration in declarations
                 if declaration.getType() is OPERATORS.ASSIGN
                     varName = declaration.child().child()
                     value = evaluateExpression declaration.getChild 1
-                    Stack.defineVariable varName, value
+                    Stack.defineVariable varName, type, value
                 else if declaration.getType() is NODES.ID
                     varName = declaration.child()
-                    Stack.defineVariable varName
+                    Stack.defineVariable varName, type
         when STATEMENTS.COUT
             for outputItem in T.getChildren()
                 io.output io.STDOUT, evaluateExpression(outputItem)
@@ -87,7 +86,7 @@ executeInstructionHelper = (T) ->
         when NODES.CLOSE_SCOPE
             Stack.closeScope()
         when NODES.FUNCALL
-            pushInstruction initFunction T
+            initFunction T
         when STATEMENTS.CIN
             allRead = yes
             for inputItem in T.getChildren()
@@ -107,6 +106,8 @@ executeInstructionHelper = (T) ->
                     Stack.setVariable id, null
                     allRead = no
             cinStack.push allRead
+        when NODES.END_FUNC_BLOCK
+            (->)()
         else
             evaluateExpression T
 
diff --git a/interpreter/stack.coffee b/interpreter/stack.coffee
index 212eb3b..f01e657 100644
--- a/interpreter/stack.coffee
+++ b/interpreter/stack.coffee
@@ -5,8 +5,8 @@ module.exports = class Stack
     @stack: []
     @currentAR: null
 
-    @pushActivationRecord: ->
-        @currentAR = { scopesStack: [], variables: {} }
+    @pushActivationRecord: (funcName, args) ->
+        @currentAR = { scopesStack: [], variables: {}, funcName: funcName, args: args }
         @stack.push @currentAR
 
     @popActivationRecord: ->
@@ -17,28 +17,28 @@ module.exports = class Stack
             if @stack.length > 0 then @stack[@stack.length - 1] else null
 
     # Parameter value is optional, if ommited means variable has been declared but not yet assigned
-    @defineVariable: (name, value = null) ->
+    @defineVariable: (name, type, value = null) ->
         assert @currentAR?
         assert (typeof name is "string")
 
-        @currentAR.variables[name] = value
+        @currentAR.variables[name] = { type: type, value: value }
 
     @getVariable: (name) ->
         assert @currentAR?
         assert (typeof name is "string")
-        assert typeof @currentAR.variables[name] isnt "undefined"
+        assert typeof @currentAR.variables[name].value isnt "undefined"
 
         if @currentAR.variables[name] is null
             throw Error.GET_VARIABLE_NOT_ASSIGNED.complete('name', name)
         else
-            @currentAR.variables[name]
+            @currentAR.variables[name].value
 
     @setVariable: (name, value) ->
         assert @currentAR?
         assert (typeof name is "string")
-        assert typeof @currentAR.variables[name] isnt "undefined"
+        assert typeof @currentAR.variables[name].value isnt "undefined"
 
-        @currentAR.variables[name] = value
+        @currentAR.variables[name].value = value
 
     @openNewScope: ->
         assert @currentAR?
diff --git a/parser/ast.coffee b/parser/ast.coffee
index 382a9fa..c03f99d 100644
--- a/parser/ast.coffee
+++ b/parser/ast.coffee
@@ -72,6 +72,7 @@ module.exports = class Ast
             CLOSE_SCOPE: 'CLOSE_SCOPE'
             FUNC_VALUE: 'FUNC_VALUE'
             CIN_VALUE: 'CIN_VALUE'
+            END_FUNC_BLOCK: 'END_FUNC_BLOCK'
         })
 
     @CASTS: Object.freeze({
@@ -101,6 +102,7 @@ module.exports = class Ast
 
     constructor: (@type, @children, @leaf = no) ->
         @instr = no
+        @instrNumber = -1
         assert (typeof @type is "string")
         assert Array.isArray(@children)
 
@@ -136,10 +138,14 @@ module.exports = class Ast
 
     setIsInstr: (@instr) ->
 
+    setInstrNumber: (@instrNumber) ->
+
     setId: (@id) ->
 
-    addChild: (child, instr=no) ->
-        child.setIsInstr yes if instr
+    addChild: (child, instr=no, instrNumber=-1) ->
+        if instr
+            child.setIsInstr yes
+            child.setInstrNumber instrNumber
         @children.push child
 
     setChild: (i, value) -> @children[i] = value
diff --git a/parser/grammar.jison b/parser/grammar.jison
index 09cd13b..38e4d77 100644
--- a/parser/grammar.jison
+++ b/parser/grammar.jison
@@ -154,7 +154,7 @@ arg
 
 block_instr
     : block_instr instruction
-        {$$.addChild($2, instr=true);}
+        {$$.addChild($2, instr=true, instrNumber=@2.first_line);}
     |
         {$$ = new yy.Ast('BLOCK-INSTRUCTIONS', []);}
     ;
@@ -206,7 +206,7 @@ if
     : IF '(' expr ')' instruction_body %prec THEN
         {$$ = new yy.Ast('IF-THEN', [$3, $5]);}
     | IF '(' expr ')' instruction_body else
-        {$$ = new yy.Ast('IF-THEN-ELSE', [$3, $5, $6]);}
+        {$6.setIsInstr(true); $6.setInstrNumber(@6.first_line); $$ = new yy.Ast('IF-THEN-ELSE', [$3, $5, $6]);}
     ;
 
 while
@@ -256,7 +256,7 @@ block_cout
 
 instruction_body
     : instruction
-        {$1.setIsInstr(true); $$ = new yy.Ast('BLOCK-INSTRUCTIONS', [$1]);}
+        {$1.setIsInstr(true); $1.setInstrNumber(@1.first_line); $$ = new yy.Ast('BLOCK-INSTRUCTIONS', [$1]);}
     | '{' block_instr '}'
         {$$ = $2;}
     ;
diff --git a/semantics/index.coffee b/semantics/index.coffee
index 6cf2397..f6cbc37 100644
--- a/semantics/index.coffee
+++ b/semantics/index.coffee
@@ -415,6 +415,7 @@ checkAndPreprocess = (ast, definedVariables, functionId) ->
 
             return TYPES.VOID
 
+# TODO: replace by jison enumerations
 enumerateInstructions = (T) ->
     for child in T.getChildren()
         child.setId ++NODE_INDEX if child.instr
@@ -504,6 +505,7 @@ preprocessFunctionAndCinNodes = (T, currentBlockInstr, currentInstr) ->
         enumerateInstructions blockInstructionsAst
         preprocessFunctionAndCinNodes blockInstructionsAst, blockInstructionsAst, blockInstructionsAst.getChild(0)
         blockInstructionsAst.getChildren().push new Ast(STATEMENTS.RETURN, []) if returnType is TYPES.VOID
+        blockInstructionsAst.getChildren().push new Ast(STATEMENTS.RETURN, []) if functionId is "main"
 
     if definedVariables.main isnt TYPES.FUNCTION
         throw Error.MAIN_NOT_DEFINED