@@ -66,6 +66,10 @@ def.symbol("defined?") do (i: In):
     let vals = i.expect("'sym")
     i.push(i.scope.hasSymbol(vals[0].getString).newVal)
 
+  def.symbol("defined-sigil?") do (i: In):
+    let vals = i.expect("'sym")
+    i.push(i.scope.hasSigil(vals[0].getString).newVal)
+  
   def.symbol("sigils") do (i: In):
     var q = newSeq[MinValue](0)
     var scope = i.scope

@@ -1,2 +1,3 @@ 
-* Added support for sigils on double-quoted strings
-* Added support for arbitrary strings as dictionary keys
+* Added support for sigils on double-quoted strings.
+* Added support for arbitrary strings as dictionary keys.
+* Added **define-sigil**, **delete-sigil**, **seal-sigil**, **unseal-sigil**, **defined-sigil?**.

@@ -18,7 +18,7 @@ : A series of characters wrapped in double quotes: "Hello, World!".
 quotation
 : A list of elements, which may also contain symbols. Quotations can be used to create heterogenous lists of elements of any data type, and also to create a block of code that will be evaluated later on (quoted program). Example: (1 2 3 + \*)
 dictionary
-: A key/value table. Dictionaries are implemented as an immediately-dequoted quotation, are enclosed in curly braces, and are represented by their symbol definitions. Note that dictionary keys are symbols and therefore can only contain characters allowed in symbols. The {#link-module||dict#} provides some operators on dictionaries.
+: A key/value table. Dictionaries are implemented as an immediately-dequoted quotation, are enclosed in curly braces, and are represented by their symbol definitions. Note that dictionary keys must start with `:`and be followed by a double-quoted string, or a single word (which can be written witbout double quotes). The {#link-module||dict#} provides some operators on dictionaries.
 
   > %sidebar%
   > Example
@@ -28,7 +28,7 @@ >
   >     {
   >         "min" :name
   >         "concatenative" :paradigm
-  >         2017 :first-release-year
+  >         2017 :"first release year"
   >     }
 
 The {#link-module||logic#} provides predicate operators to check if an element belongs to a particular data type or pseudo-type (`boolean?`, `number?`, `integer?`, `float?`, `string?`, `quotation?`, `dictionary?`).

@@ -21,11 +21,17 @@ It is possible to define symbols using the {#link-operator||lang||define#} symbol. The following min program defines a new symbol called square that duplicates the first element on the stack and multiplies the two elements:
 
      (dup *) "square" define
 
-Besides symbols, min provides a set of predefined _sigils_ as abbreviations for for commonly-used symbols. For example, the previous definition could be rewritten as follows using sigils:
+Besides symbols, you can also define sigila. min provides a set of predefined _sigils_ as abbreviations for for commonly-used symbols. For example, the previous definition could be rewritten as follows using sigils:
 
      (dup *) :square
 
-A sigil like `:` can be prepended to a single-word string instead of using the corresponding symbol. Essentially, sigils are nothing more than syntactic sugar. Currently min provides the following sigils:
+A sigil like `:` can be prepended to a double-quoted string or a single word (with no spaces) which will be treated as a string instead of using the corresponding symbol. 
+
+For example, the following executes the command `ls -al` and pushes the command return code on the atack:
+
+     !"ls -al"`
+
+Currently min provides the following sigils:
 
 +
 : Alias for {#link-operator||lang||module#}.
@@ -59,5 +65,19 @@ &
 : Alias for {#link-operator||sys||run#}.
 $
 : Alias for {#link-operator||sys||get-env#}. 
+
+Besides system sigils, you can also create your own sigils. Unlike system sigils however, user defined sigils:
+
+* have the same character restricrions as symbols
+* can only be prepended to double-quoted strings
+* can be unsealed, deleted, redefined, and sealed.
+
+Sigils can be a very powerful construct and a way to reduce boulerplate code: you can define a sigil to use as you would use any symbol which requires a single string or quoted symbol on the stack.
+
+Consider the following example:
+
+     'from-json 'j define-sigil
+     
+This will define a `j` sigil that will parse any string as JSON and convert it to its corresponding min representation.
 
 {#link-learn||quotations||Quotations#}

@@ -4,7 +4,7 @@ title: "Scopes"
 -----
 {@ _defs_.md || 0 @}
 
-As explained in [Definitions](/learn-definitions), min uses lexical scoping to resolve symbols. A *scope* is an execution context (a symbol table really) that:
+As explained in [Definitions](/learn-definitions), min uses lexical scoping to resolve symbols and sigils. A *scope* is an execution context (a symbol table really) that:
 * is created while a new quotation is being dequoted or a dictionary is created.
 * is destroyed after a quotation has been dequoted.
 * is attached to a dictionary.

@@ -92,11 +92,20 @@ 
 {#op||define||{{any}} {{sl}}||{{null}}||
 Defines a new symbol {{sl}}, containing the specified value (auto-quoted if not already a quotation).#}
 
+{#op||define-sigil||{{any}} {{sl}}||{{null}}||
+Defines a new sigil {{sl}}, containing the specified value (auto-quoted if not already a quotation).#}
+
 {#op||defined?||{{sl}}||{{b}}||
-Returns {{t}} if {{sl}} is defined, {{f}} otherwise.#}
+Returns {{t}} if the symbol {{sl}} is defined, {{f}} otherwise.#}
+
+{#op||defined-sigil?||{{sl}}||{{b}}||
+Returns {{t}} if the symbol {{sl}} is defined, {{f}} otherwise.#}
 
 {#op||delete||{{sl}}||{{null}}||
 Deletes the specified symbol {{sl}}.#}
+
+{#op||delete-sigil||{{sl}}||{{null}}||
+Deletes the specified user-defined sigil {{sl}}.#}
 
 {#op||dequote||{{q}}||{{a0p}}||
 > Pushes the contents of quotation {{q}} on the stack.
@@ -340,6 +349,9 @@ 
 {#op||seal||{{sl}}||{{null}}||
 Seals symbol {{sl}}, so that it cannot be re-assigned. #}
 
+{#op||seal-sigil||{{sl}}||{{null}}||
+Seals the user-defined sigil {{sl}}, so that it cannot be re-defined. #}
+
 {#op||set-type||{{d}} {{sl}}||{{d}}||
 Sets the type for dictionary {{d}} to {{sl}}.#}
 
@@ -436,7 +448,10 @@ {#op||unless||{{q1}} {{q2}}||{{a0p}}||
 If {{1}} evaluates to {{f}} then evaluates {{2}}.#}
 
 {#op||unseal||{{sl}}||{{null}}||
-Unseals symbol {{sl}}, so that it can be re-assigned. #}
+Unseals the user-defined symbol {{sl}}, so that it can be re-assigned. #}
+
+{#op||unseal-sigil||{{sl}}||{{null}}||
+Unseals sigil {{sl}}, so that it can be re-defined (system sigils cannot be unsealed). #}
 
 {#op||version||{{null}}||{{s}}||
 Returns the current min version number. #}

@@ -215,6 +215,17 @@ 
   ((2 < 3 and (4 > 2)) >< true) assert
 
   ((float 3) >> 3.0 ==) assert
+  
+  (
+    ("--" suffix "--" prefix) 'del define-sigil
+    del"test" "--test--" ==
+  ) assert
+  
+  (
+    ("x" prefix) 'x define-sigil
+    'x unseal-sigil 'x delete-sigil 
+    'x defined-sigil? false ==
+  ) assert
 
   report
   ; Tidy up