From 91c8a3f5148893c23b078832ab063ee81e005405 Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Sat, 20 Oct 2018 03:17:16 +0200
Subject: [PATCH 01/11] Add `read_file` macro method

---
 spec/compiler/macro/macro_methods_spec.cr | 14 ++++++++++++++
 src/compiler/crystal/macros.cr            | 11 +++++++++++
 src/compiler/crystal/macros/methods.cr    | 16 ++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/spec/compiler/macro/macro_methods_spec.cr b/spec/compiler/macro/macro_methods_spec.cr
index 67073205e8b6..355bbf82cf25 100644
--- a/spec/compiler/macro/macro_methods_spec.cr
+++ b/spec/compiler/macro/macro_methods_spec.cr
@@ -1757,4 +1757,18 @@ module Crystal
       end
     end
   end
+
+  describe "read_file" do
+    it "reads file (exists)" do
+      run(%q<
+        {{read_file("#{__DIR__}/../data/build")}}
+        >, filename = __FILE__).to_string.should eq(File.read("#{__DIR__}/../data/build"))
+    end
+
+    it "reads file (doesn't exists)" do
+      run(%q<
+        {{read_file("#{__DIR__}/../data/build_foo")}} ? 10 : 20
+        >, filename = __FILE__).to_i.should eq(20)
+    end
+  end
 end
diff --git a/src/compiler/crystal/macros.cr b/src/compiler/crystal/macros.cr
index d06e57b4d65d..5f8b975d5564 100644
--- a/src/compiler/crystal/macros.cr
+++ b/src/compiler/crystal/macros.cr
@@ -67,6 +67,17 @@ module Crystal::Macros
   def raise(message) : NoReturn
   end
 
+  # Reads a file: if it exists, returns a StringLiteral with its contents;
+  # otherwise `nil` is returned.
+  #
+  # To read a file relative to where the macro is defined, use:
+  #
+  # ```
+  # read_file("#{__DIR__}/some_file.txt")
+  # ```
+  def read_file(filename) : StringLiteral | NilLiteral
+  end
+
   # Compiles and execute a Crystal program and returns its output
   # as a `MacroId`.
   #
diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index 36c47e32ee55..56ed8722459e 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -30,6 +30,8 @@ module Crystal
         interpret_system(node)
       when "raise"
         interpret_raise(node)
+      when "read_file"
+        interpret_read_file(node)
       when "run"
         interpret_run(node)
       else
@@ -142,6 +144,20 @@ module Crystal
       raise SkipMacroException.new(@str.to_s)
     end
 
+    def interpret_read_file(node)
+      if node.args.size == 1
+        node.args[0].accept self
+        filename = @last.to_macro_id
+        if File.exists?(filename)
+          @last = StringLiteral.new(File.read(filename))
+        else
+          @last = NilLiteral.new
+        end
+      else
+        node.wrong_number_of_arguments "macro call 'read_file'", node.args.size, 1
+      end
+    end
+
     def interpret_system(node)
       cmd = node.args.map do |arg|
         arg.accept self

From 9200e3865e4a755ce9b237abbfbe0b351a7e319b Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Sun, 4 Nov 2018 23:04:27 +0100
Subject: [PATCH 02/11] Refactor run & read_file macros, as per @asterite's
 review

---
 src/compiler/crystal/macros/methods.cr | 57 ++++++++++++++------------
 1 file changed, 31 insertions(+), 26 deletions(-)

diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index 56ed8722459e..5592a77c66d6 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -145,17 +145,18 @@ module Crystal
     end
 
     def interpret_read_file(node)
-      if node.args.size == 1
-        node.args[0].accept self
-        filename = @last.to_macro_id
-        if File.exists?(filename)
-          @last = StringLiteral.new(File.read(filename))
-        else
-          @last = NilLiteral.new
-        end
-      else
+      unless node.args.size == 1
         node.wrong_number_of_arguments "macro call 'read_file'", node.args.size, 1
       end
+
+      node.args[0].accept self
+      filename = @last.to_macro_id
+      filename = find_file(filename) { }
+      if filename
+        @last = StringLiteral.new(File.read(filename))
+      else
+        @last = NilLiteral.new
+      end
     end
 
     def interpret_system(node)
@@ -179,44 +180,48 @@ module Crystal
       macro_raise(node, node.args, self)
     end
 
-    def interpret_run(node)
-      if node.args.size == 0
-        node.wrong_number_of_arguments "macro call 'run'", 0, "1+"
-      end
-
-      node.args.first.accept self
-      filename = @last.to_macro_id
-      original_filename = filename
-
+    private def find_file(filename)
       # Support absolute paths
-      if filename.starts_with?("/")
-        filename = "#{filename}.cr" unless filename.ends_with?(".cr")
-
+      if filename.starts_with?('/')
         if File.exists?(filename)
           unless File.file?(filename)
-            node.raise "error executing macro run: '#{filename}' is not a file"
+            return yield Exception.new "#{filename.inspect} is not a file"
           end
         else
-          node.raise "error executing macro run: can't find file '#{filename}'"
+          return yield Exception.new "can't find file #{filename.inspect}"
         end
       else
         begin
           relative_to = @location.try &.original_filename
           found_filenames = @program.find_in_path(filename, relative_to)
         rescue ex
-          node.raise "error executing macro run: #{ex.message}"
+          return yield ex
         end
 
         unless found_filenames
-          node.raise "error executing macro run: can't find file '#{filename}'"
+          return yield Exception.new "can't find file #{filename.inspect}"
         end
 
         if found_filenames.size > 1
-          node.raise "error executing macro run: '#{filename}' is a directory"
+          return yield Exception.new "#{filename.inspect} is a directory"
         end
 
         filename = found_filenames.first
       end
+      filename
+    end
+
+    def interpret_run(node)
+      if node.args.size == 0
+        node.wrong_number_of_arguments "macro call 'run'", 0, "1+"
+      end
+
+      node.args.first.accept self
+      original_filename = @last.to_macro_id
+
+      filename = original_filename
+      filename = "#{filename}.cr" unless filename.ends_with?(".cr")
+      filename = find_file(filename) { |ex| node.raise "error executing macro 'run': #{ex.message}" }
 
       run_args = [] of String
       node.args.each_with_index do |arg, i|

From 0f801d73d077b7efe0d62dce52faf07b37148081 Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Sun, 4 Nov 2018 23:17:46 +0100
Subject: [PATCH 03/11] Yield error message instead of Exception

---
 src/compiler/crystal/macros/methods.cr | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index 5592a77c66d6..9043467309dd 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -185,25 +185,30 @@ module Crystal
       if filename.starts_with?('/')
         if File.exists?(filename)
           unless File.file?(filename)
-            return yield Exception.new "#{filename.inspect} is not a file"
+            yield "#{filename.inspect} is not a file"
+            return
           end
         else
-          return yield Exception.new "can't find file #{filename.inspect}"
+          yield "can't find file #{filename.inspect}"
+          return
         end
       else
         begin
           relative_to = @location.try &.original_filename
           found_filenames = @program.find_in_path(filename, relative_to)
         rescue ex
-          return yield ex
+          yield ex.message
+          return
         end
 
         unless found_filenames
-          return yield Exception.new "can't find file #{filename.inspect}"
+          yield "can't find file #{filename.inspect}"
+          return
         end
 
         if found_filenames.size > 1
-          return yield Exception.new "#{filename.inspect} is a directory"
+          yield "#{filename.inspect} is a directory"
+          return
         end
 
         filename = found_filenames.first
@@ -221,7 +226,9 @@ module Crystal
 
       filename = original_filename
       filename = "#{filename}.cr" unless filename.ends_with?(".cr")
-      filename = find_file(filename) { |ex| node.raise "error executing macro 'run': #{ex.message}" }
+      filename = find_file(filename) { |error_message|
+        node.raise "error executing macro 'run': #{error_message}"
+      }
 
       run_args = [] of String
       node.args.each_with_index do |arg, i|

From 2f378a32e4056b08afa42759181bceafddded626 Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Sun, 4 Nov 2018 23:42:01 +0100
Subject: [PATCH 04/11] Pass return value of yielded block

---
 src/compiler/crystal/macros/methods.cr | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index 9043467309dd..a2e6d5f8dd12 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -185,30 +185,25 @@ module Crystal
       if filename.starts_with?('/')
         if File.exists?(filename)
           unless File.file?(filename)
-            yield "#{filename.inspect} is not a file"
-            return
+            return yield "#{filename.inspect} is not a file"
           end
         else
-          yield "can't find file #{filename.inspect}"
-          return
+          return yield "can't find file #{filename.inspect}"
         end
       else
         begin
           relative_to = @location.try &.original_filename
           found_filenames = @program.find_in_path(filename, relative_to)
         rescue ex
-          yield ex.message
-          return
+          return yield ex.message
         end
 
         unless found_filenames
-          yield "can't find file #{filename.inspect}"
-          return
+          return yield "can't find file #{filename.inspect}"
         end
 
         if found_filenames.size > 1
-          yield "#{filename.inspect} is a directory"
-          return
+          return yield "#{filename.inspect} is a directory"
         end
 
         filename = found_filenames.first

From 82fe3113f66779bb089a0d696255656780329a3f Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Tue, 6 Nov 2018 15:05:06 +0100
Subject: [PATCH 05/11] Fixes as per @straight-shoota's review

---
 src/compiler/crystal/macros.cr         |  2 +-
 src/compiler/crystal/macros/methods.cr | 66 +++++++++++++-------------
 2 files changed, 34 insertions(+), 34 deletions(-)

diff --git a/src/compiler/crystal/macros.cr b/src/compiler/crystal/macros.cr
index 5f8b975d5564..e78c3e393514 100644
--- a/src/compiler/crystal/macros.cr
+++ b/src/compiler/crystal/macros.cr
@@ -67,7 +67,7 @@ module Crystal::Macros
   def raise(message) : NoReturn
   end
 
-  # Reads a file: if it exists, returns a StringLiteral with its contents;
+  # Reads a file: if it exists, returns a `StringLiteral` with its contents;
   # otherwise `nil` is returned.
   #
   # To read a file relative to where the macro is defined, use:
diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index a2e6d5f8dd12..eb36bc2c8674 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -4,6 +4,37 @@ require "semantic_version"
 
 module Crystal
   class MacroInterpreter
+    private def find_file(filename)
+      # Support absolute paths
+      if filename.starts_with?('/')
+        if File.exists?(filename)
+          unless File.file?(filename)
+            return yield "#{filename.inspect} is not a file"
+          end
+        else
+          return yield "can't find file #{filename.inspect}"
+        end
+      else
+        begin
+          relative_to = @location.try &.original_filename
+          found_filenames = @program.find_in_path(filename, relative_to)
+        rescue ex
+          return yield ex.message
+        end
+
+        unless found_filenames
+          return yield "can't find file #{filename.inspect}"
+        end
+
+        if found_filenames.size > 1
+          return yield "#{filename.inspect} is a directory"
+        end
+
+        filename = found_filenames.first
+      end
+      filename
+    end
+
     def interpret_top_level_call(node)
       interpret_top_level_call?(node) ||
         node.raise("undefined macro method: '#{node.name}'")
@@ -180,37 +211,6 @@ module Crystal
       macro_raise(node, node.args, self)
     end
 
-    private def find_file(filename)
-      # Support absolute paths
-      if filename.starts_with?('/')
-        if File.exists?(filename)
-          unless File.file?(filename)
-            return yield "#{filename.inspect} is not a file"
-          end
-        else
-          return yield "can't find file #{filename.inspect}"
-        end
-      else
-        begin
-          relative_to = @location.try &.original_filename
-          found_filenames = @program.find_in_path(filename, relative_to)
-        rescue ex
-          return yield ex.message
-        end
-
-        unless found_filenames
-          return yield "can't find file #{filename.inspect}"
-        end
-
-        if found_filenames.size > 1
-          return yield "#{filename.inspect} is a directory"
-        end
-
-        filename = found_filenames.first
-      end
-      filename
-    end
-
     def interpret_run(node)
       if node.args.size == 0
         node.wrong_number_of_arguments "macro call 'run'", 0, "1+"
@@ -221,9 +221,9 @@ module Crystal
 
       filename = original_filename
       filename = "#{filename}.cr" unless filename.ends_with?(".cr")
-      filename = find_file(filename) { |error_message|
+      filename = find_file(filename) do |error_message|
         node.raise "error executing macro 'run': #{error_message}"
-      }
+      end
 
       run_args = [] of String
       node.args.each_with_index do |arg, i|

From 0820ae88b508b6770f43fce1607bba3014aa988c Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Wed, 7 Nov 2018 01:46:11 +0100
Subject: [PATCH 06/11] Don't use relative path resolution in 'read_file' macro

---
 src/compiler/crystal/macros/methods.cr | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index eb36bc2c8674..24ca4da881f0 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -182,8 +182,7 @@ module Crystal
 
       node.args[0].accept self
       filename = @last.to_macro_id
-      filename = find_file(filename) { }
-      if filename
+      if File.exists?(filename)
         @last = StringLiteral.new(File.read(filename))
       else
         @last = NilLiteral.new

From f13cccba693ba3810ab360de9a7e181d27b4fa90 Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Wed, 7 Nov 2018 11:56:43 +0100
Subject: [PATCH 07/11] Add NOTE and spec regarding relative paths

---
 spec/compiler/macro/macro_methods_spec.cr | 32 +++++++++++++++++------
 src/compiler/crystal/macros.cr            |  2 ++
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/spec/compiler/macro/macro_methods_spec.cr b/spec/compiler/macro/macro_methods_spec.cr
index 355bbf82cf25..e7d844247024 100644
--- a/spec/compiler/macro/macro_methods_spec.cr
+++ b/spec/compiler/macro/macro_methods_spec.cr
@@ -1759,16 +1759,32 @@ module Crystal
   end
 
   describe "read_file" do
-    it "reads file (exists)" do
-      run(%q<
-        {{read_file("#{__DIR__}/../data/build")}}
-        >, filename = __FILE__).to_string.should eq(File.read("#{__DIR__}/../data/build"))
+    context "with absolute path" do
+      it "reads file (exists)" do
+        run(%q<
+          {{read_file("#{__DIR__}/../data/build")}}
+          >, filename = __FILE__).to_string.should eq(File.read("#{__DIR__}/../data/build"))
+      end
+
+      it "reads file (doesn't exists)" do
+        run(%q<
+          {{read_file("#{__DIR__}/../data/build_foo")}} ? 10 : 20
+          >, filename = __FILE__).to_i.should eq(20)
+      end
     end
 
-    it "reads file (doesn't exists)" do
-      run(%q<
-        {{read_file("#{__DIR__}/../data/build_foo")}} ? 10 : 20
-        >, filename = __FILE__).to_i.should eq(20)
+    context "with relative path" do
+      it "reads file (exists)" do
+        run(%q<
+          {{read_file("spec/compiler/data/build")}}
+          >, filename = __FILE__).to_string.should eq(File.read("spec/compiler/data/build"))
+      end
+
+      it "reads file (doesn't exists)" do
+        run(%q<
+          {{read_file("spec/compiler/data/build_foo")}} ? 10 : 20
+          >, filename = __FILE__).to_i.should eq(20)
+      end
     end
   end
 end
diff --git a/src/compiler/crystal/macros.cr b/src/compiler/crystal/macros.cr
index e78c3e393514..4119b9ec68e2 100644
--- a/src/compiler/crystal/macros.cr
+++ b/src/compiler/crystal/macros.cr
@@ -75,6 +75,8 @@ module Crystal::Macros
   # ```
   # read_file("#{__DIR__}/some_file.txt")
   # ```
+  #
+  # NOTE: Relative paths are resolved to the current working directory.
   def read_file(filename) : StringLiteral | NilLiteral
   end
 

From a2d70e4f56d35bbbb7dc591e3f0a442b40645856 Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Wed, 7 Nov 2018 14:38:30 +0100
Subject: [PATCH 08/11] Use more apt File.file? check instead of File.exists?

---
 src/compiler/crystal/macros/methods.cr | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index 24ca4da881f0..c837dedcb8d6 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -182,7 +182,7 @@ module Crystal
 
       node.args[0].accept self
       filename = @last.to_macro_id
-      if File.exists?(filename)
+      if File.file?(filename)
         @last = StringLiteral.new(File.read(filename))
       else
         @last = NilLiteral.new

From 9aa5f09b15c06bdebc57931e71fc0b4493a7c9cd Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Wed, 7 Nov 2018 14:40:12 +0100
Subject: [PATCH 09/11] Refactor filename resolution in `find_file` to be more
 consistent

---
 src/compiler/crystal/macros/methods.cr | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index c837dedcb8d6..c638b77d5c82 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -5,6 +5,8 @@ require "semantic_version"
 module Crystal
   class MacroInterpreter
     private def find_file(filename)
+      filename = "#{filename}.cr" unless filename.ends_with?(".cr")
+
       # Support absolute paths
       if filename.starts_with?('/')
         if File.exists?(filename)
@@ -219,7 +221,6 @@ module Crystal
       original_filename = @last.to_macro_id
 
       filename = original_filename
-      filename = "#{filename}.cr" unless filename.ends_with?(".cr")
       filename = find_file(filename) do |error_message|
         node.raise "error executing macro 'run': #{error_message}"
       end

From 29adc3534508fc761b3566904d4c6f6e2c758eb4 Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Wed, 7 Nov 2018 19:53:55 +0100
Subject: [PATCH 10/11] Revert `run` macro refactors

---
 src/compiler/crystal/macros/methods.cr | 67 ++++++++++++--------------
 1 file changed, 30 insertions(+), 37 deletions(-)

diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index c638b77d5c82..8069d4cc57b4 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -4,39 +4,6 @@ require "semantic_version"
 
 module Crystal
   class MacroInterpreter
-    private def find_file(filename)
-      filename = "#{filename}.cr" unless filename.ends_with?(".cr")
-
-      # Support absolute paths
-      if filename.starts_with?('/')
-        if File.exists?(filename)
-          unless File.file?(filename)
-            return yield "#{filename.inspect} is not a file"
-          end
-        else
-          return yield "can't find file #{filename.inspect}"
-        end
-      else
-        begin
-          relative_to = @location.try &.original_filename
-          found_filenames = @program.find_in_path(filename, relative_to)
-        rescue ex
-          return yield ex.message
-        end
-
-        unless found_filenames
-          return yield "can't find file #{filename.inspect}"
-        end
-
-        if found_filenames.size > 1
-          return yield "#{filename.inspect} is a directory"
-        end
-
-        filename = found_filenames.first
-      end
-      filename
-    end
-
     def interpret_top_level_call(node)
       interpret_top_level_call?(node) ||
         node.raise("undefined macro method: '#{node.name}'")
@@ -218,11 +185,37 @@ module Crystal
       end
 
       node.args.first.accept self
-      original_filename = @last.to_macro_id
+      filename = @last.to_macro_id
+      original_filename = filename
+
+      # Support absolute paths
+      if filename.starts_with?("/")
+        filename = "#{filename}.cr" unless filename.ends_with?(".cr")
 
-      filename = original_filename
-      filename = find_file(filename) do |error_message|
-        node.raise "error executing macro 'run': #{error_message}"
+        if File.exists?(filename)
+          unless File.file?(filename)
+            node.raise "error executing macro run: '#{filename}' is not a file"
+          end
+        else
+          node.raise "error executing macro run: can't find file '#{filename}'"
+        end
+      else
+        begin
+          relative_to = @location.try &.original_filename
+          found_filenames = @program.find_in_path(filename, relative_to)
+        rescue ex
+          node.raise "error executing macro run: #{ex.message}"
+        end
+
+        unless found_filenames
+          node.raise "error executing macro run: can't find file '#{filename}'"
+        end
+
+        if found_filenames.size > 1
+          node.raise "error executing macro run: '#{filename}' is a directory"
+        end
+
+        filename = found_filenames.first
       end
 
       run_args = [] of String

From 2ae9e53af5de0f51f67170cca32a2d07f1be5ff9 Mon Sep 17 00:00:00 2001
From: Sijawusz Pur Rahnama <sija@sija.pl>
Date: Wed, 7 Nov 2018 20:59:19 +0100
Subject: [PATCH 11/11] Move `interpret_read_file` definition under
 lexicographically correct position

---
 src/compiler/crystal/macros/methods.cr | 28 +++++++++++++-------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index 8069d4cc57b4..0a3dbfaab64b 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -144,20 +144,6 @@ module Crystal
       raise SkipMacroException.new(@str.to_s)
     end
 
-    def interpret_read_file(node)
-      unless node.args.size == 1
-        node.wrong_number_of_arguments "macro call 'read_file'", node.args.size, 1
-      end
-
-      node.args[0].accept self
-      filename = @last.to_macro_id
-      if File.file?(filename)
-        @last = StringLiteral.new(File.read(filename))
-      else
-        @last = NilLiteral.new
-      end
-    end
-
     def interpret_system(node)
       cmd = node.args.map do |arg|
         arg.accept self
@@ -179,6 +165,20 @@ module Crystal
       macro_raise(node, node.args, self)
     end
 
+    def interpret_read_file(node)
+      unless node.args.size == 1
+        node.wrong_number_of_arguments "macro call 'read_file'", node.args.size, 1
+      end
+
+      node.args[0].accept self
+      filename = @last.to_macro_id
+      if File.file?(filename)
+        @last = StringLiteral.new(File.read(filename))
+      else
+        @last = NilLiteral.new
+      end
+    end
+
     def interpret_run(node)
       if node.args.size == 0
         node.wrong_number_of_arguments "macro call 'run'", 0, "1+"