Ability to cast int/double <-> string

[unode]

Motivation:

seq.filter(min_identity_pc=ARGV[1])

fails to typecheck since ARGV[] are strings.

and similarly:

cutoff = 95
...
seq.filter(min_identity_pc=cutoff)
...
write(... ofile="/path/file_" + cutoff + ".txt")

Will either fail on the first if cutoff is a string or the second if an integer/double.

---

One possibility I explored was to add a method number.to_string() to all numeric types but I hit a limitation in that different types cannot have a method with the same name. The code compiles but when executed NGLess gives a confusing error (paraphrasing) method 'to_string' doesn't exist, did you mean 'to_string'?

So I ended up with:

diff --git a/NGLess/BuiltinFunctions.hs b/NGLess/BuiltinFunctions.hs
index 2486533..cb5d680 100644
--- a/NGLess/BuiltinFunctions.hs
+++ b/NGLess/BuiltinFunctions.hs
@@ -145,6 +145,11 @@ builtinMethods =
     ,MethodInfo (MethodName "avg_quality") NGLRead Nothing NGLDouble [] True []
     ,MethodInfo (MethodName "fraction_at_least") NGLRead (Just NGLInteger) NGLDouble [] True []
     ,MethodInfo (MethodName "n_to_zero_quality") NGLRead Nothing NGLRead [] True [FunctionCheckMinNGLessVersion (0,8)]
+
+    -- NGLDouble
+    ,MethodInfo (MethodName "double_to_string") NGLDouble Nothing NGLString [] True []
+    -- NGLInteger
+    ,MethodInfo (MethodName "int_to_string") NGLInteger Nothing NGLString [] True []
     ]
 
 filterArgs =
diff --git a/NGLess/Interpret.hs b/NGLess/Interpret.hs
index e99e54c..e97acdd 100644
--- a/NGLess/Interpret.hs
+++ b/NGLess/Interpret.hs
@@ -95,6 +95,7 @@ import Data.FastQ
 import NGLess.NGLEnvironment
 import NGLess.NGError
 
+import Interpretation.Language
 import Interpretation.Map
 import Interpretation.Count
 import Interpretation.FastQ
@@ -484,6 +485,8 @@ executePreprocess v _ _ = unreachable ("executePreprocess: Cannot handle this in
 executeMethod :: MethodName -> NGLessObject -> Maybe NGLessObject -> [(T.Text, NGLessObject)] -> InterpretationROEnv NGLessObject
 executeMethod method (NGOMappedRead samline) arg kwargs = runNGLess (executeMappedReadMethod method samline arg kwargs)
 executeMethod method (NGOShortRead sr) arg kwargs = runNGLess (executeShortReadsMethod method sr arg kwargs)
+executeMethod method (NGODouble double) arg kwargs = runNGLess (executeDoubleTypeMethod method double arg kwargs)
+executeMethod method (NGOInteger int) arg kwargs = runNGLess (executeIntegerTypeMethod method int arg kwargs)
 executeMethod m self arg kwargs = throwShouldNotOccur ("Method " ++ show m ++ " with self="++show self ++ " arg="++ show arg ++ " kwargs="++show kwargs ++ " is not implemented")
 
 
diff --git a/NGLess/Interpretation/Language.hs b/NGLess/Interpretation/Language.hs
new file mode 100644
index 0000000..9e54b17
--- /dev/null
+++ b/NGLess/Interpretation/Language.hs
@@ -0,0 +1,22 @@
+{- Copyright 2015-2018 NGLess Authors
+ - License: MIT
+ -}
+
+{-# LANGUAGE RankNTypes, FlexibleContexts #-}
+
+module Interpretation.Language
+    ( executeDoubleTypeMethod
+    , executeIntegerTypeMethod
+    ) where
+
+import Data.Text (pack)
+import Language
+import NGLess
+
+executeDoubleTypeMethod :: MethodName -> Double -> Maybe NGLessObject -> KwArgsValues -> NGLess NGLessObject
+executeDoubleTypeMethod (MethodName "double_to_string") number Nothing [] = return . NGOString . pack . show $ number
+executeDoubleTypeMethod m self arg kwargs = throwShouldNotOccur ("Method " ++ show m ++ " with self="++show self ++ " arg="++ show arg ++ " kwargs="++show kwargs ++ " is not implemented")
+
+executeIntegerTypeMethod :: MethodName -> Integer -> Maybe NGLessObject -> KwArgsValues -> NGLess NGLessObject
+executeIntegerTypeMethod (MethodName "int_to_string") number Nothing [] = return . NGOString . pack . show $ number
+executeIntegerTypeMethod m self arg kwargs = throwShouldNotOccur ("Method " ++ show m ++ " with self="++show self ++ " arg="++ show arg ++ " kwargs="++show kwargs ++ " is not implemented")

Alternatively I also considered a function to_string(variable) but ran into similar limitations in that different functions are necessary to handle different types.

The above code doesn't address the ARGV[] -> int/double use-case. I'd probably go for string.to_int() and string.to_double() and error if the transformation isn't possible.

Any suggestions on better ways to address the need for casting variables?

[luispedro]

Not having the ability to have more than one method with the same name across different types is obviously a silly limitation.