✅[#1] Change some operations to support "truthyness"

Changes "if", "filter", "and" and "or" to take any type as arguments
but the return types should still align.

This change just assumes an implicit "!!" call around the boolean arguments.

src/parser.ts

@@ -46,7 +46,7 @@ export const defaultContext = makeContext({
   missing: f(array(string), array(string)),
   missing_some: f(number, array(string), array(string)),
   // Logic and Boolean Operations
-  if: forall([a], f(bool, a, a, a)),
+  if: forall([a, b], f(a, b, b, b)),
   // TODO: should the parameters of (in-)equaility be of the same type 🤔
   // forcing === and !== isn't a eslint rule for nothing...
   '==': forall([a, b], f(a, b, bool)),
@@ -55,8 +55,8 @@ export const defaultContext = makeContext({
   '!==': forall([a, b], f(a, b, bool)),
   '!': forall([a], f(a, bool)),
   '!!': forall([a], f(a, bool)),
-  or: f(bool, bool, bool),
-  and: f(bool, bool, bool),
+  or: forall([a, b], f(a, b, bool)),
+  and: forall([a, b], f(a, b, bool)),
   // Numeric Operations
   '>': f(number, number, bool),
   '>=': f(number, number, bool),
@@ -80,8 +80,8 @@ export const defaultContext = makeContext({
   // Array Operations
   // forall a b. :: [a] -> (a -> b) -> [b]
   map: forall([a, b], f(array(a), f(a, b), array(b))),
-  // forall a. :: [a] -> (a -> bool) -> [a]
-  filter: forall([a], f(array(a), f(a, bool), array(a))),
+  // forall a truthy. :: [a] -> (a -> truthy) -> [a]
+  filter: forall([a, b], f(array(a), f(a, b), array(a))),
   // forall a b. :: [b] -> (a -> b -> a) -> a -> a
   reduce: forall([a, b], f(array(b), f(a, b, a), a, a)),
   // forall a. :: [a] -> (a -> bool) -> bool