implement template strings

7 files changed, 118 insertions, 14 deletions

diff --git a/alv/ast.moon b/alv/ast.moon
index 04e6627..4d0ecae 100644
--- a/alv/ast.moon
+++ b/alv/ast.moon
@@ -33,6 +33,7 @@
   -- @treturn string the exact string this Node was parsed from
 
 import Cell, RootCell from require 'alv.cell'
+import TemplateString from require 'alv.template_string'
 import Constant from require 'alv.result.const'
 import Dummy from require 'alv.dummy'
 import Tag from require 'alv.tag'
@@ -40,6 +41,7 @@ import Tag from require 'alv.tag'
 {
   :Cell
   :RootCell
+  :TemplateString
   :Constant
   :Dummy
   :Tag
diff --git a/alv/base/builtin.moon b/alv/base/builtin.moon
index 558a65a..4b8ee5a 100644
--- a/alv/base/builtin.moon
+++ b/alv/base/builtin.moon
@@ -6,6 +6,7 @@
 -- See `builtin` and `invoke` for examples.
 --
 -- @classmod Builtin
+import TemplateString from require 'alv.template_string'
 
 class Builtin
 --- Builtin interface.
@@ -107,7 +108,16 @@ class Builtin
     else
       builtin\setup nil
 
-    builtin\eval scope, cell\tail!
+    tail = {}
+    for child in *cell\tail!
+      if child.__class == TemplateString
+        table.insert tail, child.string
+        for inner in *child.children
+          table.insert tail, inner
+      else
+        table.insert tail, child
+
+    builtin\eval scope, tail
 
   __tostring: => "<#{@@__name}[#{@tag}] #{@head}>"
   __inherited: (cls) => cls.__base.__tostring = @__tostring
diff --git a/alv/base/init.moon b/alv/base/init.moon
index bfe9123..a5d0b88 100644
--- a/alv/base/init.moon
+++ b/alv/base/init.moon
@@ -20,6 +20,7 @@
 -- @see type.Primitive
 -- @see type.Array
 -- @see type.Struct
+-- @see TemplateString
 -- @see RTNode
 -- @see Error
 
@@ -31,6 +32,7 @@ import Input from require 'alv.base.input'
 import const, sig, evt, any from require 'alv.base.match'
 import Constant, SigStream, EvtStream from require 'alv.result'
 import T, Primitive, Array, Struct from require 'alv.type'
+import TemplateString from require 'alv.template_string'
 import RTNode from require 'alv.rtnode'
 import Error from require 'alv.error'
 
@@ -49,6 +51,7 @@ import Error from require 'alv.error'
   -- Types
   :T, :Primitive, :Array, :Struct
 
+  :TemplateString
   :RTNode
   :Error
 }
diff --git a/alv/cell.moon b/alv/cell.moon
index ced9032..7b6cf61 100644
--- a/alv/cell.moon
+++ b/alv/cell.moon
@@ -98,7 +98,7 @@ class Cell
   clone: (parent) =>
     tag = @tag\clone parent
     children = [child\clone parent for child in *@children]
-    Cell tag, children, @white
+    @@ tag, children, @white
 
   --- stringify this Cell.
   --
@@ -155,11 +155,6 @@ class RootCell extends Cell
   head: => Constant.sym 'do'
   tail: => @children
 
-  clone: (parent) =>
-    tag = @tag\clone parent
-    children = [child\clone parent for child in *@children]
-    RootCell tag, children, @white
-
   stringify: =>
     buf = ''
     buf ..= @white[0]
@@ -184,4 +179,5 @@ class RootCell extends Cell
 {
   :Cell
   :RootCell
+  :TemplateString
 }
diff --git a/alv/parsing.moon b/alv/parsing.moon
index 7174c06..d5ec313 100644
--- a/alv/parsing.moon
+++ b/alv/parsing.moon
@@ -2,7 +2,7 @@
 -- Lpeg Grammar for parsing `alive` code.
 --
 -- @module parsing
-import Cell, RootCell, Constant, Tag from require 'alv.ast'
+import Cell, RootCell, Constant, TemplateString, Tag from require 'alv.ast'
 import R, S, P, V, C, Ct from require 'lpeg'
 
 -- whitespace
@@ -30,21 +30,25 @@ float = (digit^1 * '.' * digit^0) + (digit^0 * '.' * digit^1)
 num = ((P '-')^-1 * (float + fract + int)) / Constant\parse 'num'
 
 atom = num + sym + str
-
 expr = (V 'cell') + atom
-explist = Ct mspace * ((V 'expr') * (space * (V 'expr'))^0 * mspace)^-1
+
+tplcont = ((P '\\"') + (P '\\\\') + (1 - (P '"') - (P '#')))^1 / 1
+tplstr = (P '#"') * ((P '##') / 1 + ('#' * expr) + tplcont)^0 * '"' / TemplateString\parse
+
+expitem = tplstr + expr
+explist = Ct mspace * (expitem * (space * expitem)^0 * mspace)^-1
 
 tag = (P '[') * (digit^1 / Tag.parse) * (P ']')
 cell = (P '(') * tag^-1 * explist * (P ')') / Cell.parse
 
 root = P {
   explist / RootCell.parse
-  :expr, :cell
+  :cell
 }
 
 cell = P {
   'cell'
-  :expr, :cell
+  :cell
 }
 
 program = root * -1
diff --git a/alv/template_string.moon b/alv/template_string.moon
new file mode 100644
index 0000000..bd6ae0f
--- /dev/null
+++ b/alv/template_string.moon
@@ -0,0 +1,83 @@
+----
+-- A string with substitutions, partially implements the `AST` interface.
+--
+-- Is automatically "splatted" into multiple expressions when the containing
+-- `Cell` is evaluated: the original string (str=), but with with substitution
+-- markers like `#{1}`, `#{2}` and so on and one expression for each substitution.
+--
+-- `#` symbols in the original string are escaped to `##`.
+--
+-- @classmod TemplateString
+import Constant from require 'alv.result'
+
+-- @type TemplateString
+class TemplateString
+--- AST interface
+--
+-- `TemplateString` partially implements the `AST` interface.
+-- @section ast
+
+  --- create a clone with its own identity.
+  --
+  -- creates a clone of this TemplateString by cloning all child expressions
+  -- recursively.
+  --
+  -- @tparam Tag parent
+  -- @treturn TemplateString
+  clone: (parent) =>
+    children = [child\clone parent for child in *@children]
+    @@ @string, children
+
+  --- stringify this TemplateString.
+  --
+  -- if `depth` is passed, does not faithfully recreate the original string but
+  -- rather create useful debug output.
+  --
+  -- @tparam[opt] int depth the maximum depth, defaults to infinite
+  -- @treturn string the exact string this TemplateString was parsed from
+  stringify: (depth=-1) =>
+    children = ['#' .. child\stringify depth for child in *@children]
+    str = @@.subst @.string!, (i) -> '#' .. @children[i]\stringify depth
+    '#"' .. str .. '"'
+
+--- static functions
+-- @section static
+
+  new: (@string, @children) =>
+
+  --- apply substitutions to a template string.
+  --
+  -- This also reverses the escaping that the parser applied.
+  --
+  -- @classmethod
+  -- @tparam string str the evaluated `TemplateString.string`
+  -- @tparam function fn function called with index i to obtain string to substitute
+  -- @treturn string
+  @subst: (str, fn) ->
+    str = str\gsub '##', '#'
+    str\gsub '#{(%d+)}', (i) -> fn tonumber i
+
+  --- parse a TemplateString (for parsing with Lpeg).
+  --
+  -- @classmethod
+  -- @tparam {string|AST,...} pieces
+  -- @treturn TemplateString
+  @parse: (...) =>
+    string = ''
+    children = {}
+
+    i = 1
+    for elem in *{...}
+      string ..= if elem == '##' then elem
+      elseif 'string' == type elem then elem\gsub '#', '##'
+      else
+        table.insert children, elem
+        '#{' .. #children .. '}'
+
+    string = Constant.str string
+
+    @@ string, children
+
+{
+  :TemplateString
+}
diff --git a/spec/internal/parsing_spec.moon b/spec/internal/parsing_spec.moon
index 09d5b85..534155f 100644
--- a/spec/internal/parsing_spec.moon
+++ b/spec/internal/parsing_spec.moon
@@ -1,5 +1,4 @@
-import space, atom, expr, explist, cell, program, comment
-  from require 'alv.parsing'
+import space, atom, cell, program, comment from require 'alv.parsing'
 import Constant from require 'alv'
 import Logger from require 'alv.logger'
 Logger\init 'silent'
@@ -91,6 +90,13 @@ describe 'Cell', ->
     assert.is.equal 2, #node.children
     assert.is.equal 42, node.tag.value
 
+  test 'template strings', ->
+    node = verify_parse cell, '( hi #" string with #3#5 some #(= "contents") "
+                                "friend" )'
+
+    assert.is.equal 3, #node.children
+    assert.is.equal (Constant.str 'friend'), node.children[3]
+
 describe 'RootCell parsing', ->
   describe 'handles whitespace', ->
     verify = (str) ->