diff --git a/compiler/evals.nim b/compiler/evals.nim
index fa24d2b7af..f89417dc80 100644
--- a/compiler/evals.nim
+++ b/compiler/evals.nim
@@ -1446,7 +1446,6 @@ proc evalAux(c: PEvalContext, n: PNode, flags: TEvalFlags): PNode =
     result = n
   else: InternalError(n.info, "evalAux: " & $n.kind)
   if result == nil:
-    debug n
     InternalError(n.info, "evalAux: returned nil " & $n.kind)
   inc(gNestedEvals)
 
diff --git a/compiler/main.nim b/compiler/main.nim
index f61288ff10..047b3ff1d6 100644
--- a/compiler/main.nim
+++ b/compiler/main.nim
@@ -7,16 +7,17 @@
 #    distribution, for details about the copyright.
 #
 
-# implements the command dispatcher and several commands as well as the
-# module handling
+# implements the command dispatcher and several commands
 
 import 
   llstream, strutils, ast, astalgo, lexer, syntaxes, renderer, options, msgs, 
-  os, lists, condsyms, rodread, rodwrite, ropes, trees, times,
+  os, condsyms, rodread, rodwrite, times,
   wordrecg, sem, semdata, idents, passes, docgen, extccomp,
-  cgen, jsgen, cgendata, json, nversion,
+  cgen, jsgen, json, nversion,
   platform, nimconf, importer, passaux, depends, evals, types, idgen,
-  tables, docgen2, service, magicsys, parser, crc, ccgutils, sigmatch
+  tables, docgen2, service, parser, modules, ccgutils, sigmatch, ropes, lists
+
+from magicsys import SystemModule, resetSysTypes
 
 const
   has_LLVM_Backend = false
@@ -24,191 +25,6 @@ const
 when has_LLVM_Backend:
   import llvmgen
 
-proc MainCommand*()
-
-# ------------------ module handling -----------------------------------------
-
-type
-  TNeedRecompile = enum Maybe, No, Yes, Probing, Recompiled
-  TCrcStatus = enum crcNotTaken, crcCached, crcHasChanged, crcNotChanged
-
-  TModuleInMemory = object
-    compiledAt: float
-    crc: TCrc32
-    deps: seq[int32] ## XXX: slurped files are not currently tracked
-    needsRecompile: TNeedRecompile
-    crcStatus: TCrcStatus
-
-var
-  gCompiledModules: seq[PSym] = @[]
-  gMemCacheData: seq[TModuleInMemory] = @[]
-    ## XXX: we should implement recycling of file IDs
-    ## if the user keeps renaming modules, the file IDs will keep growing
-
-proc getModule(fileIdx: int32): PSym =
-  if fileIdx >= 0 and fileIdx < gCompiledModules.len:
-    result = gCompiledModules[fileIdx]
-  else:
-    result = nil
-
-template compiledAt(x: PSym): expr =
-  gMemCacheData[x.position].compiledAt
-
-template crc(x: PSym): expr =
-  gMemCacheData[x.position].crc
-
-proc crcChanged(fileIdx: int32): bool =
-  InternalAssert fileIdx >= 0 and fileIdx < gMemCacheData.len
-  
-  template updateStatus =
-    gMemCacheData[fileIdx].crcStatus = if result: crcHasChanged
-                                       else: crcNotChanged
-    # echo "TESTING CRC: ", fileIdx.toFilename, " ", result
-  
-  case gMemCacheData[fileIdx].crcStatus:
-  of crcHasChanged:
-    result = true
-  of crcNotChanged:
-    result = false
-  of crcCached:
-    let newCrc = crcFromFile(fileIdx.toFilename)
-    result = newCrc != gMemCacheData[fileIdx].crc
-    gMemCacheData[fileIdx].crc = newCrc
-    updateStatus()
-  of crcNotTaken:
-    gMemCacheData[fileIdx].crc = crcFromFile(fileIdx.toFilename)
-    result = true
-    updateStatus()
-
-proc doCRC(fileIdx: int32) =
-  if gMemCacheData[fileIdx].crcStatus == crcNotTaken:
-    # echo "FIRST CRC: ", fileIdx.ToFilename
-    gMemCacheData[fileIdx].crc = crcFromFile(fileIdx.toFilename)
-
-proc addDep(x: Psym, dep: int32) =
-  growCache gMemCacheData, dep
-  gMemCacheData[x.position].deps.safeAdd(dep)
-
-proc resetModule(fileIdx: int32) =
-  # echo "HARD RESETTING ", fileIdx.toFilename
-  gMemCacheData[fileIdx].needsRecompile = Yes
-  gCompiledModules[fileIdx] = nil
-  cgendata.gModules[fileIdx] = nil
-  resetSourceMap(fileIdx)
-
-proc resetAllModules =
-  for i in 0..gCompiledModules.high:
-    if gCompiledModules[i] != nil:
-      resetModule(i.int32)
-
-  # for m in cgenModules(): echo "CGEN MODULE FOUND"
-
-proc checkDepMem(fileIdx: int32): TNeedRecompile  =
-  template markDirty =
-    resetModule(fileIdx)
-    return Yes
-
-  if gMemCacheData[fileIdx].needsRecompile != Maybe:
-    return gMemCacheData[fileIdx].needsRecompile
-
-  if optForceFullMake in gGlobalOptions or
-     crcChanged(fileIdx):
-       markDirty
-  
-  if gMemCacheData[fileIdx].deps != nil:
-    gMemCacheData[fileIdx].needsRecompile = Probing
-    for dep in gMemCacheData[fileIdx].deps:
-      let d = checkDepMem(dep)
-      if d in { Yes, Recompiled }:
-        # echo fileIdx.toFilename, " depends on ", dep.toFilename, " ", d
-        markDirty
-  
-  gMemCacheData[fileIdx].needsRecompile = No
-  return No
-
-proc newModule(fileIdx: int32): PSym =
-  # We cannot call ``newSym`` here, because we have to circumvent the ID
-  # mechanism, which we do in order to assign each module a persistent ID. 
-  new(result)
-  result.id = - 1             # for better error checking
-  result.kind = skModule
-  let filename = fileIdx.toFilename
-  result.name = getIdent(splitFile(filename).name)
-  if not isNimrodIdentifier(result.name.s):
-    rawMessage(errInvalidModuleName, result.name.s)
-  
-  result.owner = result       # a module belongs to itself
-  result.info = newLineInfo(fileIdx, 1, 1)
-  result.position = fileIdx
-  
-  growCache gMemCacheData, fileIdx
-  growCache gCompiledModules, fileIdx
-  gCompiledModules[result.position] = result
-  
-  incl(result.flags, sfUsed)
-  initStrTable(result.tab)
-  StrTableAdd(result.tab, result) # a module knows itself
-
-proc compileModule(fileIdx: int32, flags: TSymFlags): PSym =
-  result = getModule(fileIdx)
-  if result == nil:
-    growCache gMemCacheData, fileIdx
-    gMemCacheData[fileIdx].needsRecompile = Probing
-    result = newModule(fileIdx)
-    #var rd = handleSymbolFile(result)
-    var rd: PRodReader
-    result.flags = result.flags + flags
-    if gCmd in {cmdCompileToC, cmdCompileToCpp, cmdCheck, cmdIdeTools}:
-      rd = handleSymbolFile(result)
-      if result.id < 0: 
-        InternalError("handleSymbolFile should have set the module\'s ID")
-        return
-    else:
-      result.id = getID()
-    processModule(result, nil, rd)
-    if optCaasEnabled in gGlobalOptions:
-      gMemCacheData[fileIdx].compiledAt = gLastCmdTime
-      gMemCacheData[fileIdx].needsRecompile = Recompiled
-      doCRC fileIdx
-  else:
-    if checkDepMem(fileIdx) == Yes:
-      result = CompileModule(fileIdx, flags)
-    else:
-      result = gCompiledModules[fileIdx]
-
-proc importModule(s: PSym, fileIdx: int32): PSym =
-  # this is called by the semantic checking phase
-  result = compileModule(fileIdx, {})
-  if optCaasEnabled in gGlobalOptions: addDep(s, fileIdx)
-  if sfSystemModule in result.flags:
-    LocalError(result.info, errAttemptToRedefine, result.Name.s)
-
-proc includeModule(s: PSym, fileIdx: int32): PNode =
-  result = syntaxes.parseFile(fileIdx)
-  if optCaasEnabled in gGlobalOptions:
-    growCache gMemCacheData, fileIdx
-    addDep(s, fileIdx)
-    doCrc(fileIdx)
-
-proc `==^`(a, b: string): bool =
-  try:
-    result = sameFile(a, b)
-  except EOS:
-    result = false
-
-proc compileSystemModule =
-  if magicsys.SystemModule == nil:
-    SystemFileIdx = fileInfoIdx(options.libpath/"system.nim")
-    discard CompileModule(SystemFileIdx, {sfSystemModule})
-
-proc CompileProject(projectFile = gProjectMainIdx) =
-  let systemFileIdx = fileInfoIdx(options.libpath / "system.nim")
-  if projectFile == SystemFileIdx:
-    discard CompileModule(projectFile, {sfMainModule, sfSystemModule})
-  else:
-    compileSystemModule()
-    discard CompileModule(projectFile, {sfMainModule})
-
 proc rodPass =
   if optSymbolFiles in gGlobalOptions:
     registerPass(rodwritePass)
@@ -323,13 +139,6 @@ proc InteractivePasses =
   registerPass(semPass)
   registerPass(evalPass)
 
-var stdinModule: PSym
-proc makeStdinModule: PSym =
-  if stdinModule == nil:
-    stdinModule = newModule(fileInfoIdx"stdin")
-    stdinModule.id = getID()
-  result = stdinModule
-
 proc CommandInteractive =
   msgs.gErrorMax = high(int)  # do not stop after first error
   InteractivePasses()
@@ -341,18 +150,6 @@ proc CommandInteractive =
     incl(m.flags, sfMainModule)
     processModule(m, LLStreamOpenStdIn(), nil)
 
-proc execute*(program: string) =
-  passes.gIncludeFile = includeModule
-  passes.gImportModule = importModule
-  initDefines()
-  LoadConfigs(DefaultConfig)
-  InteractivePasses()
-  appendStr(searchPaths, options.libpath)
-  compileSystemModule()
-  var m = makeStdinModule()
-  incl(m.flags, sfMainModule)
-  processModule(m, LLStreamOpen(program), nil)
-
 const evalPasses = [verbosePass, semPass, evalPass]
 
 proc evalNim(nodes: PNode, module: PSym) =
@@ -477,7 +274,7 @@ const
   SimiluateCaasMemReset = false
   PrintRopeCacheStats = false
 
-proc MainCommand =
+proc MainCommand* =
   when SimiluateCaasMemReset:
     gGlobalOptions.incl(optCaasEnabled)
       
diff --git a/compiler/modules.nim b/compiler/modules.nim
new file mode 100644
index 0000000000..ef6af3d69a
--- /dev/null
+++ b/compiler/modules.nim
@@ -0,0 +1,200 @@
+#
+#
+#           The Nimrod Compiler
+#        (c) Copyright 2013 Andreas Rumpf
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## implements the module handling
+
+import
+  ast, astalgo, magicsys, crc, rodread, msgs, cgendata, sigmatch, options, 
+  idents, os, lexer, idgen, passes, syntaxes
+
+type
+  TNeedRecompile* = enum Maybe, No, Yes, Probing, Recompiled
+  TCrcStatus* = enum crcNotTaken, crcCached, crcHasChanged, crcNotChanged
+
+  TModuleInMemory* = object
+    compiledAt*: float
+    crc*: TCrc32
+    deps*: seq[int32] ## XXX: slurped files are not currently tracked
+    needsRecompile*: TNeedRecompile
+    crcStatus*: TCrcStatus
+
+var
+  gCompiledModules: seq[PSym] = @[]
+  gMemCacheData*: seq[TModuleInMemory] = @[]
+    ## XXX: we should implement recycling of file IDs
+    ## if the user keeps renaming modules, the file IDs will keep growing
+
+proc getModule(fileIdx: int32): PSym =
+  if fileIdx >= 0 and fileIdx < gCompiledModules.len:
+    result = gCompiledModules[fileIdx]
+
+template compiledAt(x: PSym): expr =
+  gMemCacheData[x.position].compiledAt
+
+template crc(x: PSym): expr =
+  gMemCacheData[x.position].crc
+
+proc crcChanged(fileIdx: int32): bool =
+  InternalAssert fileIdx >= 0 and fileIdx < gMemCacheData.len
+  
+  template updateStatus =
+    gMemCacheData[fileIdx].crcStatus = if result: crcHasChanged
+                                       else: crcNotChanged
+    # echo "TESTING CRC: ", fileIdx.toFilename, " ", result
+  
+  case gMemCacheData[fileIdx].crcStatus:
+  of crcHasChanged:
+    result = true
+  of crcNotChanged:
+    result = false
+  of crcCached:
+    let newCrc = crcFromFile(fileIdx.toFilename)
+    result = newCrc != gMemCacheData[fileIdx].crc
+    gMemCacheData[fileIdx].crc = newCrc
+    updateStatus()
+  of crcNotTaken:
+    gMemCacheData[fileIdx].crc = crcFromFile(fileIdx.toFilename)
+    result = true
+    updateStatus()
+
+proc doCRC(fileIdx: int32) =
+  if gMemCacheData[fileIdx].crcStatus == crcNotTaken:
+    # echo "FIRST CRC: ", fileIdx.ToFilename
+    gMemCacheData[fileIdx].crc = crcFromFile(fileIdx.toFilename)
+
+proc addDep(x: Psym, dep: int32) =
+  growCache gMemCacheData, dep
+  gMemCacheData[x.position].deps.safeAdd(dep)
+
+proc resetModule*(fileIdx: int32) =
+  # echo "HARD RESETTING ", fileIdx.toFilename
+  gMemCacheData[fileIdx].needsRecompile = Yes
+  gCompiledModules[fileIdx] = nil
+  cgendata.gModules[fileIdx] = nil
+  resetSourceMap(fileIdx)
+
+proc resetAllModules* =
+  for i in 0..gCompiledModules.high:
+    if gCompiledModules[i] != nil:
+      resetModule(i.int32)
+
+  # for m in cgenModules(): echo "CGEN MODULE FOUND"
+
+proc checkDepMem(fileIdx: int32): TNeedRecompile =
+  template markDirty =
+    resetModule(fileIdx)
+    return Yes
+
+  if gMemCacheData[fileIdx].needsRecompile != Maybe:
+    return gMemCacheData[fileIdx].needsRecompile
+
+  if optForceFullMake in gGlobalOptions or
+     crcChanged(fileIdx):
+       markDirty
+  
+  if gMemCacheData[fileIdx].deps != nil:
+    gMemCacheData[fileIdx].needsRecompile = Probing
+    for dep in gMemCacheData[fileIdx].deps:
+      let d = checkDepMem(dep)
+      if d in {Yes, Recompiled}:
+        # echo fileIdx.toFilename, " depends on ", dep.toFilename, " ", d
+        markDirty
+  
+  gMemCacheData[fileIdx].needsRecompile = No
+  return No
+
+proc newModule(fileIdx: int32): PSym =
+  # We cannot call ``newSym`` here, because we have to circumvent the ID
+  # mechanism, which we do in order to assign each module a persistent ID. 
+  new(result)
+  result.id = - 1             # for better error checking
+  result.kind = skModule
+  let filename = fileIdx.toFilename
+  result.name = getIdent(splitFile(filename).name)
+  if not isNimrodIdentifier(result.name.s):
+    rawMessage(errInvalidModuleName, result.name.s)
+  
+  result.owner = result       # a module belongs to itself
+  result.info = newLineInfo(fileIdx, 1, 1)
+  result.position = fileIdx
+  
+  growCache gMemCacheData, fileIdx
+  growCache gCompiledModules, fileIdx
+  gCompiledModules[result.position] = result
+  
+  incl(result.flags, sfUsed)
+  initStrTable(result.tab)
+  StrTableAdd(result.tab, result) # a module knows itself
+
+proc compileModule*(fileIdx: int32, flags: TSymFlags): PSym =
+  result = getModule(fileIdx)
+  if result == nil:
+    growCache gMemCacheData, fileIdx
+    gMemCacheData[fileIdx].needsRecompile = Probing
+    result = newModule(fileIdx)
+    #var rd = handleSymbolFile(result)
+    var rd: PRodReader
+    result.flags = result.flags + flags
+    if gCmd in {cmdCompileToC, cmdCompileToCpp, cmdCheck, cmdIdeTools}:
+      rd = handleSymbolFile(result)
+      if result.id < 0: 
+        InternalError("handleSymbolFile should have set the module\'s ID")
+        return
+    else:
+      result.id = getID()
+    processModule(result, nil, rd)
+    if optCaasEnabled in gGlobalOptions:
+      gMemCacheData[fileIdx].compiledAt = gLastCmdTime
+      gMemCacheData[fileIdx].needsRecompile = Recompiled
+      doCRC fileIdx
+  else:
+    if checkDepMem(fileIdx) == Yes:
+      result = CompileModule(fileIdx, flags)
+    else:
+      result = gCompiledModules[fileIdx]
+
+proc importModule*(s: PSym, fileIdx: int32): PSym {.procvar.} =
+  # this is called by the semantic checking phase
+  result = compileModule(fileIdx, {})
+  if optCaasEnabled in gGlobalOptions: addDep(s, fileIdx)
+  if sfSystemModule in result.flags:
+    LocalError(result.info, errAttemptToRedefine, result.Name.s)
+
+proc includeModule*(s: PSym, fileIdx: int32): PNode {.procvar.} =
+  result = syntaxes.parseFile(fileIdx)
+  if optCaasEnabled in gGlobalOptions:
+    growCache gMemCacheData, fileIdx
+    addDep(s, fileIdx)
+    doCrc(fileIdx)
+
+proc `==^`(a, b: string): bool =
+  try:
+    result = sameFile(a, b)
+  except EOS:
+    result = false
+
+proc compileSystemModule* =
+  if magicsys.SystemModule == nil:
+    SystemFileIdx = fileInfoIdx(options.libpath/"system.nim")
+    discard CompileModule(SystemFileIdx, {sfSystemModule})
+
+proc CompileProject*(projectFile = gProjectMainIdx) =
+  let systemFileIdx = fileInfoIdx(options.libpath / "system.nim")
+  if projectFile == SystemFileIdx:
+    discard CompileModule(projectFile, {sfMainModule, sfSystemModule})
+  else:
+    compileSystemModule()
+    discard CompileModule(projectFile, {sfMainModule})
+
+var stdinModule: PSym
+proc makeStdinModule*(): PSym =
+  if stdinModule == nil:
+    stdinModule = newModule(fileInfoIdx"stdin")
+    stdinModule.id = getID()
+  result = stdinModule
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index a94d89caaa..28ea50a158 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -1473,7 +1473,10 @@ proc semWhen(c: PContext, n: PNode, semCheck = true): PNode =
     of nkElifBranch, nkElifExpr: 
       checkSonsLen(it, 2)
       var e = semConstExpr(c, it.sons[0])
-      if e.kind != nkIntLit: InternalError(n.info, "semWhen")
+      if e.kind != nkIntLit: 
+        # can happen for cascading errors, assume false
+        # InternalError(n.info, "semWhen")
+        discard
       elif e.intVal != 0 and result == nil:
         setResult(it.sons[1]) 
     of nkElse, nkElseExpr:
diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index 041baf1260..a3e108a34b 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -12,8 +12,10 @@
 
 import 
   intsets, ast, astalgo, semdata, types, msgs, renderer, lookups, semtypinst,
-  magicsys, condsyms, idents, lexer, options, parampatterns, strutils,
-  docgen
+  magicsys, condsyms, idents, lexer, options, parampatterns, strutils
+
+when not defined(noDocgen):
+  import docgen
 
 type
   TCandidateState* = enum 
diff --git a/compiler/suggest.nim b/compiler/suggest.nim
index 892afc05ea..85e256cbb3 100644
--- a/compiler/suggest.nim
+++ b/compiler/suggest.nim
@@ -46,7 +46,8 @@ proc SymToStr(s: PSym, isLocal: bool, section: string, li: TLineInfo): string =
   result.add(sep)
   result.add($ToColumn(li))
   result.add(sep)
-  result.add(s.extractDocComment.escape)
+  when not defined(noDocgen):
+    result.add(s.extractDocComment.escape)
 
 proc SymToStr(s: PSym, isLocal: bool, section: string): string = 
   result = SymToStr(s, isLocal, section, s.info)