---
title: WLang
version: 0.8.4
sections:
  - id: about
    name: About
    file: about.rdoc
  - id: overview
    name: Overview
    file: overview.rdoc
  - id: rulesets
    name: Rulesets
    file: rulesets.wtpl
    links: 'spec["rulesets"].reverse'
  - id: dialects
    name: Dialects
    file: dialects.wtpl
  - id: hosting
    name: Hosting language
    file: hosting.rdoc
  - id: glossary
    name: Glossary
    file: glossary.wtpl
  - id: symbols
    name: Tag symbols
    file: symbols.wtpl
glossary:
  - term: template 
    definition: |-
      Source code respecting the wlang grammar, and attached to a given <em>wlang 
      dialect</em>.
    example: |-
      <tt>Hello ${name}</tt>
  - term: dialect
    definition: |-
      Basically, <em>dialect</em> is used as a synonym for (programming) <em>language</em>.
      However _wlang_ uses a tree of dialects, allowing specializations: <tt>sql/sybase</tt>
      for example is the qualified name of a sub-dialect 'sybase' of the 'sql' dialect. 
      Dialects come with associated _encoders_.
    example: |-
      <tt>sql/sybase</tt>
  - term: wlang dialect
    definition: |-
      When we talk about a <em>wlang dialect</em>, we are actually refering to some 
      specialization of the wlang tag-based grammar: <tt>wlang/xhtml</tt> for example
      is the templating language _wlang_ proposes to generate xhtml pages. An 
      example of source code in that dialect has been shown before.
      In addition to its encoders a <em>wlang dialect</em> comes with its sets of _tags_ 
      and associated _rules_.
    example: |-
      <tt>wlang/xhtml</tt>
  - term: encoder
    definition: |-
      Text transformation (algorithm) applying some encoding conventions of a portion
      of a the target language generated by a dialect. HTML entities-encoding, SQL's back-quoting 
      are examples of encoders. Encoders are accessible through their qualified name (dialect/encoder).
    example: |-
      <tt>xhtml/entities-encoding</tt><br/><tt>sql/single-quoting</tt>
  - term: ruleset
    definition: |-
      Reusable set of <em>tags</em> associated to <em>rule</em>s.
    example: |-
      <tt>Imperative ruleset</tt><br/><tt>Encoding rulset</tt>
  - term: wlang tag
    definition: |-
      Special tags in the template, starting with wlang symbols and a number of wlang 
      blocks. A tag is associated with a wlang rule. 
    example: |-
      <tt>${...}</tt><br/><tt>?{...}{...}{...}</tt>
  - term: rule
    definition: |-
      Transformation semantics of a given <em>tag</em>. When wlang instantiates a
      template it simply replaces <em>wlang tags</em> by some <em>replacement value</em>
      (which is always a string). This value is computed by the rule attached to 
      the tag. Rule definition (see Rulesets tab on top of the page)
      explicitly describes the number of blocks it expects, in which dialect they 
      are parsed and instantiated and the way the replacement value is computed.
    example: |-
      <tt>^{wlang/active-string}{...}</tt><br/>
      Instantiates #1, looking for an encoder qualified name. Instantiates #2 in 
      the current dialect. Encode #2's instantiation using encoder found in (#1)
      and return the result as replacement value.
  - term: context
    definition: |-  
      Some rules allow code to be executed in the <em>hosting language</em> (the 
      definition explicitly announce it by putting <tt>wlang/hosted</tt> in the corresponding
      block). When doing so, this code is in fact executed in a given context that 
      provides the execution semantics.
  - term: hosting language
    definition: |-
      language (or framework) that executes wlang. More precisely, the hosting language
      is the one that rules what is considered as an executable expression in tags that
      relies on some execution semantics (like !{...} for example). See the 'Hosting language'
      section to learn more.
    example: |-
      ruby
rulesets: 
  - name: Basic 
    description: |-
      The Basic ruleset is commonly installed on any dialect and provides access to _wlang_ 
      foundations inside your template: requesting the hosting language to execute some expression,
      changing the current dialect and encoding text. 
    examples:
      - ["wlang/active-string", "Hello !{name}",                       "Hello O'Neil"]
      - ["wlang/active-string", "Hello %{wlang/dummy}{!{name}}",       "Hello !{name}"]
      - ["wlang/dummy",         "Hello %{wlang/dummy}{!{name}}",       "Hello %{wlang/dummy}{!{name}}"]
      - ["wlang/active-string", "Hello ^{plain-text/upcase}{${name}}", "Hello O'NEIL"]
    rules:
      # !{wlang/hosted}
      - name:      "execution"
        symbol:    "!"
        signature: "!{wlang/hosted}"
        definition: |-
          Instantiates #1, looking for an expression of the hosting language. Evaluates it, 
          looking for any object. Converts it to a string (using to_s for example if Ruby is
          the hosting language) and returns the result as replacement value.
      
      # %{wlang/active-string}{...}
      - name:      "modulation"
        symbol:    "%"
        signature: "%{wlang/active-string}{...}"
        definition: |-
          Instantiates #1, looking for a dialect qualified name. Instantiates #2 
          according to the rules defined by that dialect and returns the #2's 
          instantiation as replacement value.
      
      # ^{wlang/active-string}{...}
      - name:      "encoding"
        symbol:    "^"
        signature: "^{wlang/active-string}{...}"
        definition: |-
          Instantiates #1, looking for an encoder qualified name. Instantiates #2 in 
          the current dialect. Encode #2's instantiation using encoder found in (#1) and
          returns encoding as replacement value.
      
      # %!{wlang/active-string using ... with ...}{...}
      - name:      "recursive-application"
        symbol:    "%!"
        signature: "%!{wlang/active-string <using>? <with>?}{...}"
        definition: |-
          Instantiates #1, looking for a dialect qualified name. Instantiates #2 
          in the current dialect. Instantiates #2's instantiation in the dialect found
          in #1, using context installed by 'using ...' and 'with ...'. Returns this 
          instantiation as replacement value (this really advanced rule allows 
          metaprogramming).  
      
      # ${wlang/hosted}
      - name:      "injection"
        symbol:    "$"
        signature: "${wlang/hosted}"
        definition: Same semantics as execution (intended to be overrided).
      
      # +{wlang/hosted}
      - name:      "inclusion"
        symbol:    "+"
        signature: "+{wlang/hosted}"
        definition: Same semantics as execution (intended to be overrided).

  - name: Encoding
    description: |-
      Almost all languages require escaping/encoding in specific situations: quoted string literals
      always come with an escaping mechanism (unfortunately different from one language to another), 
      html requires entities-encoding, etc. The Encoding ruleset proposes shortcut tags for encoding. 
      Note that these shortcuts are written in such a way that they don't depend on the effective 
      dialect. _wlang_ hides language and vendors differences!
    examples:
      - ["wlang/xhtml", "Hello &{name}",                       "Hello name"]
      - ["wlang/xhtml", "Hello &{<script>}",                   "Hello &lt;script&gt;"]
      - ["wlang/xhtml", "Hello &;{<script>}",                  "Hello &lt;script&gt;"]
      - ["wlang/ruby",  "puts 'Hello &'{name}'",               "puts 'Hello name'"]
      - ["wlang/ruby",  "puts 'Hello &'{!{name}}'",            "puts 'Hello O\'Neil'"]
      - ["wlang/ruby",  "puts 'Hello ' << '{name}'",           "puts 'Hello ' << 'O\'Neil'"]
      - ["wlang/sql",   "... WHERE name='{name}'",             "... WHERE name='O\'Neil'"]
      - ["wlang/sql/sybase",  "... WHERE name='{name}'",       "... WHERE name='O''Neil'"]
    rules:
      # &{...}
      - name:       "main-encoding"
        symbol:     "&"
        signature:  "&{...}"
        definition: "<tt>^{+{@parser.current_dialect}/main-encoding}{#1}</tt>"
    
      # &;{...}
      - name:       "entities-encoding"
        symbol:     "&;"
        signature:  "&;{...}"
        definition: "<tt>^{+{@parser.current_dialect}/entities-encoding}{#1}</tt>"
    
      # &'{...}
      - name:       "single-quoting"
        symbol:     "&'"
        signature:  "&'{...}"
        definition: "<tt>^{+{@parser.current_dialect}/single-quoting}{#1}</tt>"
    
      # &;{...}
      - name:       "double-quoting"
        symbol:     '&"'
        signature:  '&"{...}'
        definition: "<tt>^{+{@parser.current_dialect}/double-quoting}{#1}</tt>"
    
      # ${wlang/hosted}
      - name:      "injection"
        symbol:    "$"
        signature: "${wlang/hosted}"
        definition: "<tt>&{+{#1}}</tt>"
    
      # '{wlang/hosted}
      - name:      "single-quoted"
        symbol:    "'"
        signature: "'{wlang/hosted}"
        definition: |-
          <tt>'&'{+{#1}}</tt> (first single quote is kept in the result)
    
      # "{wlang/hosted}
      - name:      "double-quoted"
        symbol:    '"'
        signature: '"{wlang/hosted}'
        definition: |-
          <tt>"&"{+{#1}}</tt> (first double quote is kept in the result)
        
  - name: Imperative
    description: |-
      Instantiating conditionally and iterating collection elements are common code generation tasks. 
      The Imperative dialect provides these features.
    examples:
      - ["wlang/*", '?{true}{then}{else}',                         'then']
      - ["wlang/*", '?{/th/ =~ "not tat"}{then}{else}',            'else']
      - ["wlang/*", '?{authors.include? "blambeau"}{yes}{no}',    'yes']
      - ["wlang/*", '[*{authors as a}{"{a}"}{, }]', '["blambeau", "llambeau", "ancailliau"]']
    rules:
      # ?{wlang/hosted}{...}{...}
      - name:      "conditional<br/>(third block is optional)"
        symbol:    "?"
        signature: "?{wlang/hosted}{...}{...}"
        definition: |-
          Instantiates #1, looking for an expression in the hosting language. 
          Evaluates it, looking for a boolean value (according to boolean semantics 
          of the hosting language). If true, instantiates #2, otherwise instantiates 
          #3 if present, returning instantiation as replacement value.
    
      # *{wlang/hosted as x}{...}{...}
      - name:      "enumeration<br/>(third block is optional)"
        symbol:    "*"
        signature: "*{wlang/hosted <as x>?}{...}{...}"
        definition: |-
          Instantiates #1, looking for an expression in the hosting language. Evaluates 
          it, looking for an enumerable. Iterates all its elements, instantiating #2 for 
          each of them (the iterated value is set under name x in the scope). If #3 is 
          present, it is instantiated between elements. Replacement is the concatenation
          of all these instantiations.

  - name: Context
    description: |-
      Complex templates come with specific needs. The ability to manipulate the context and the current
      scope is provided by the Context ruleset. All are variants of 'saving previous instantiations' in 
      scope variables...
    examples:
      - ["wlang/*", '={name as n}{Hello +{n}}',                      "Hello O'Neil"]
      - ["wlang/*", '={name as n}Hello +{n}',                        "Hello O'Neil"]
      - ["wlang/*", '#={name}{blambeau}{Hello +{name}} and +{name}', "Hello blambeau and O'Neil"]
      - ["wlang/*", '#={name}{blambeau}Hello +{name} and +{name}',   "Hello blambeau and blambeau"]
      - ["wlang/*", '={author as name}{Hello +{name}} and +{name}', "Hello blambeau and O'Neil"]
      - ["wlang/*", '={author as name}Hello +{name} and +{name}',   "Hello blambeau and blambeau"]
      - ["wlang/*", '%={wlang/dummy as hello}{Hello +{name}}{+{hello}}', "Hello +{name}"]
      - ["wlang/*", '^={plain-text/upcase as name}{+{author}}{Hello +{name}} and +{name}', "Hello BLAMBEAU and O'Neil"]
      - ["wlang/*", '^={plain-text/upcase as name}{+{author}}Hello +{name} and +{name}', "Hello BLAMBEAU and BLAMBEAU"]
      
    rules: 
      # ={wlang/hosted as x}{...}
      - name:      "assignment<br/>(second block is optional)"
        symbol:    "="
        signature: "={wlang/hosted <as x>}{...}"
        definition: |-
            Instantiates #1, looking for an expression in the hosting language. Evaluates 
            it, looking for any object. Without second block, expands the current scope with 
            'x' being bound to evaluation result. Otherwise, branches the current scope for
            the second block instantiation only and bind 'x' the same way (i.e. x will not be 
            available outside the second block). Returns an empty string as replacement value.
      # %={wlang/active-string as x}{...}{...}
      - name:      "modulo-assignment<br/>(third block is optional)"
        symbol:    "%="
        signature: "%={wlang/active-string <as x>}{...}{...}"
        definition: |-
            Instantiates #1, looking for a dialect qualified name. Instantiates #2 according 
            to the rules defined by that dialect. Without third block, expands the current 
            scope with 'x' being bound to #2's instantiation. Otherwise, branches the current 
            scope for the third block instantiation only and binds 'x' the same way (i.e. x will 
            not be available outside the third block). Returns an empty string as replacement 
            value.
      # #={wlang/active-string}{...}{...}
      - name:      "block-assignment<br/>(third block is optional)"
        symbol:    "="
        signature: "#={wlang/active-string <as x>}{...}{...}"
        definition: |-
          <tt>%={+{@parser.current_dialect} as #1}{#2}{#3}</tt>
      # ^={wlang/active-string as x}{...}{...}
      - name:      "encoding-assignment<br/>(third block is optional)"
        symbol:    "^="
        signature: "^={wlang/active-string <as x>}{...}{...}"
        definition: |-
          <tt>%={+{@parser.current_dialect} as x}{^{#1}{#2}}{#3}</tt>

  - name: Buffering
    description: |-
      The Buffering ruleset is probably one of the more useful. It allows you to load text and data files, 
      to change the current output buffer (for generating multiple files for example) and even to start 
      the instantiation on other templates.
    rules:
      # <<{wlang/uri}
      - name:      "input"
        symbol:    "<<"
        signature: "<<{wlang/uri}"
        definition: |-
          Instantiates #1, looking for an uri. Returns the text content of the found 
          uri (#1) as replacement value.
      # >>{wlang/uri}
      - name:      "output"
        symbol:    ">>"
        signature: ">>{wlang/uri}{...}"
        definition: |-
          Instantiates #1, looking for an uri. Instantiates #2 in the current dialect,
          using the file found in #1 as output buffer. Returns an empty string as replacement
          value.
      # <<={wlang/uri as x}{...}
      - name:      "data-assignment"
        symbol:    "<<="
        signature: "<<={wlang/uri <as x>}{...}"
        definition: |-
          Instantiates #1, looking for an uri. Loads data provided by this uri, based on the
          file extension (typically .yml or .rb). Without second block, expands the current scope 
          with 'x' being bound to the data. Otherwise, branches the current scope for the second 
          block instantiation only and binds 'x' the same way (i.e. x will not be available outside 
          the second block). Returns an empty string as replacement value.
      # <<+{wlang/uri with ...}
      - name:      "input-inclusion"
        symbol:    "<<+"
        signature: "<<+{wlang/uri <using>? <with>?}"
        definition: |-
          Instantiates #1, looking for an uri. Instantiates the _wlang_ template at this location
          (the dialect is infered from the file extension) in a fresh new scope built from the _with_
          expression. Returns this instantiation as replacement value.

symbols:
  - name: exclamation mark
    symbol: '!'
    meaning: execution
    remark: should never be overrided as single
  - name: 'caret/circumflex'
    symbol: '^'
    meaning: explicit encoding
    remark: should never be overrided as single
  - name: percent
    symbol: '%'
    meaning: modulation
    remark: should never be overrided as single
  - name: double quote
    symbol: '"'
    meaning: double-quoting
  - name: dollar
    symbol: '$'
    meaning: 'main-encoding'
  - name: ampersand
    symbol: '&'
    meaning: encoding
  - name: single quote
    symbol: "'"
    meaning: single-quoting
  - name: asterisk
    symbol: '*'
    meaning: iteration
  - name: plus
    symbol: '+'
    meaning: inclusion
  - name: question mark
    symbol: '?'
    meaning: condition
  - name: at symbol
    symbol: '@'
    meaning: linking
  - name: tilde
    symbol: '~'
    meaning: matching
  - name: number sign  
    symbol: '#'
  - name: comma
    symbol: ','
  - name: minus (dash)
    symbol: '-'
  - name: dot
    symbol: '.'
  - name: forward slash
    symbol: '/'
  - name: colon
    symbol: ':'
  - name: 'semi-colon'
    symbol: ';'
  - name: equal sign
    symbol: '='
  - name: less than
    symbol: '<'
  - name: greater than
    symbol: '>'
  - name: vertical bar
    symbol: '|'
  - name: underscore
    symbol: '_'
    remark: cannot be used as tag symbol; reserved for escaping in future versions
  - name: back slash
    symbol: \
    remark: cannot be used as tag symbol; reserved for escaping in current version
  - name: left parenthesis
    symbol: '('
    remark: cannot be used as tag symbol; reserved for block delimiter 
  - name: right parenthesis
    symbol: ')'
    remark: cannot be used as tag symbol; reserved for block delimiter 
  - name: left bracket
    symbol: '['
    remark: cannot be used as tag symbol; reserved for block delimiter 
  - name: right bracket
    symbol: ']'
    remark: cannot be used as tag symbol; reserved for block delimiter 
  - name: left brace
    symbol: '{'
    remark: cannot be used as tag symbol; reserved for block delimiter 
  - name: right brace
    symbol: '}'
    remark: cannot be used as tag symbol; reserved for block delimiter