M minpkg/lib/min_lang.nim → minpkg/lib/min_lang.nim

@@ -198,6 +198,7 @@ var inExpects= newSeq[string](0)
     var inVars = newSeq[string](0)
     var outExpects= newSeq[string](0)
     var outVars = newSeq[string](0)
+    var rawOutVars = newSeq[string](0)
     var generics: CritBitTree[string]
     var origGenerics: CritBitTree[string]
     var o = false
@@ -239,11 +240,16 @@ raiseInvalid("typeclasses can only have one input value")
             inExpects.add v
       else:
         if v[0] != ':' and v[0] != '^':
-          raiseInvalid("No mapping symbol specified in signature at position $#" % $(c+1))
+          raiseInvalid("No capturing symbol specified in signature at position $#" % $(c+1))
         else:
           if o:
+            if v[0] == '^' and outExpects[outExpects.len-1] != "quot":
+              raiseInvalid("Only quotations can be captured to a lambda, found $# instead at position $#" % [outExpects[outExpects.len-1], $(c+1)])
+            rawOutVars.add v
             outVars.add v[1..v.len-1]
           else:
+            if v[0] == '^':
+              raiseInvalid("A lambda capturing symbol was specified in signature at position $#. Lambda capturing symbols are only allowed for output values" % $(c+1))
             inVars.add v[1..v.len-1]
       c.inc()
     if not o:
@@ -286,9 +292,9 @@ except MinReturnException:
           discard
         # Validate output
         for k in 0..outVars.len-1:
-          #i.pushSym outVars[k]
-          #let x = i.peek
-          let x = i.scope.symbols[outVars[k]].val
+          var x = i.scope.symbols[outVars[k]].val
+          if rawOutVars[k][0] == ':':
+            x = x.qVal[0]
           if t == "constructor":
             x.objType = n
           let o = outExpects[k]
@@ -302,7 +308,6 @@ break
           else:
             r = i.validate(x, o, generics)
           if not r:
-            discard i.pop
             var tp = o
             if generics.hasKey(o):
               tp = generics[o]

M next-release.md → next-release.md

@@ -1,2 +1,29 @@ 
+
+### Fixes
+
 * Added `===` at the end of integrated help descriptions (#127).
+
+### Mew additions
+ 
 * New symbol: [parent-scope](https://min-lang.org/reference-lang/#op-parent-scope) (#117).
+
+### Notable changes
+
+#### Lambda capturing in operator output values
+
+You can now specify a lambda to be captured to an output value, like this:
+
+     (
+       symbol square
+       (==> quot ^o)
+       (
+         (dup *) ~o
+       )
+     ) ::
+     
+Essentially, this allows you to push a lambda on the stack from an operator.
+
+Note that:
+* Lambdas must be captured using the `^` sigil in signatures and bound using `lambda-bind` in the operator body.
+* Lambdas cannot be captured in input values (they have already been pushed on the stack).
+* Requiring a lambda as an output value effectively bypasses stack pollution checks. While this can be useful at times, use with caution!

M site/contents/learn-operators.md → site/contents/learn-operators.md

@@ -48,6 +48,11 @@ * have no built-in validation of input and output values.
 * do not support the `return` symbol to immediately end their execution.
 * have no built-in stack pollution checks.
 
+> %tip
+> Tip
+> 
+> You can use {#link-operator||lang||lambda-bind#} to re-set a previously set lambda.
+
 ## Sigils
 
 Besides symbols, you can also define sigils. min provides a set of predefined _sigils_ as abbreviations for for commonly-used symbols. 
@@ -172,6 +177,25 @@ > %tip%
 > Tip
 > 
 > `typeclass:`-prefixed symbols are just like ordinary shmbols: they are lexically scoped, they can be sealed, unsealed and deleted.
+
+#### Capturing lambdas
+
+You can also specify a lambda to be captured to an output value, like this:
+
+     (
+       symbol square
+       (==> quot ^o)
+       (
+         (dup *) ~o
+       )
+     ) ::
+     
+Essentially, this allows you to push a lambda on the stack from an operator.
+
+Note that:
+* Lambdas must be captured using the `^` sigil in signatures and bound using {#link-operator||lang||lambda-bind#} in the operator body.
+* Lambdas cannot be captured in input values (they have already been pushed on the stack).
+* Requiring a lambda as an output value effectively bypasses stack pollution checks. While this can be useful at times, use with caution!
 
 ### Generics