diff --git a/DEVELOP.md b/DEVELOP.md
index 534426d..009e6f2 100644
--- a/DEVELOP.md
+++ b/DEVELOP.md
@@ -54,6 +54,23 @@ simple
     | END
     | STDERRREDIRECT
     ;
+
+type : typeItem ('|' typeItem)* ;
+
+typeItem
+    : 'int'
+    | 'float'
+    | 'string'
+    | 'bool'
+    | typeList
+    | typeQuote
+    | genericType
+    ;
+
+typeQuote : '(' type* -- type* ')' ;
+typeList : homogeneousList | heterogeneousList ;
+homogeneousList : '[' type '*' ']' ;
+heterogeneousList : '[' type+ ']' ;
 ```
 
 Key Types:
@@ -65,7 +82,7 @@ MShellObject
     MShellBool
     MShellQuotation
     MShellString
-
+    MShellFloat
 ```
 
 ## References
diff --git a/lib/std.msh b/lib/std.msh
index 18841d7..f34f26f 100644
--- a/lib/std.msh
+++ b/lib/std.msh
@@ -1,5 +1,7 @@
 # Standard library for mshell
 
+type numeric int | float
+
 # each (list quote: (item --) --)
 def each
     over len each-len! # Get total length
@@ -19,6 +21,12 @@ end
 
 # map (list quote -- list)
 def map
+(
+    [T*]: list
+    (T -- U): q
+    --
+    [U*]
+)
     over len map-len! # Get total length
     0 map-idx! # Index
     [] map-accum! # Accumulator