From 430e40a7b365e47b8994c6c49256e16ebacebe8d Mon Sep 17 00:00:00 2001
From: odino <alessandro.nadalin@gmail.com>
Date: Mon, 26 Aug 2019 17:30:17 +0400
Subject: [PATCH] Bas-style interpolation in strings, closes #169

Now you can embed variables inside strings by prefixing them with
`$`. Literal `$` simply need a `\`. This aligns the string interpolation
syntax with commands, and makes it easier to switch between running
a command (`` `$some $command` ``) and echoing it (`echo("$some $command")`).
---
 README.md                   |  2 +-
 docs/README.md              |  2 +-
 docs/types/string.md        | 19 +++++++++++++++++++
 evaluator/evaluator.go      |  2 +-
 evaluator/evaluator_test.go | 16 ++++++++++++++++
 examples/ip-sum.abs         |  2 +-
 scripts/release.abs         |  4 ++--
 7 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index adca0011..63684f62 100644
--- a/README.md
+++ b/README.md
@@ -83,7 +83,7 @@ if !res.ok {
 ip = res.json().ip
 total = ip.split(".").map(int).sum()
 if total > 100 {
-    echo("The sum of [%s] is a large number, %s.", ip, total)
+    echo("The sum of [$ip] is a large number, $total.")
 }
 ```
 
diff --git a/docs/README.md b/docs/README.md
index 97384915..e2cb260e 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -80,7 +80,7 @@ if !res.ok {
 ip = res.json().ip
 total = ip.split(".").map(int).sum()
 if total > 100 {
-    echo("The sum of [%s] is a large number, %s.", ip, total)
+    echo("The sum of [$ip] is a large number, $total.")
 }
 ```
 
diff --git a/docs/types/string.md b/docs/types/string.md
index ca1adc43..4266628a 100644
--- a/docs/types/string.md
+++ b/docs/types/string.md
@@ -83,6 +83,25 @@ To test for the existence of substrings within strings use the `in` operator:
 "xyz" in "string"   # false
 ```
 
+## Interpolation
+
+You can also replace parts of the string with variables
+declared within your program using the `$` symbol:
+
+``` bash
+file = "/etc/hosts"
+x = "File name is: $file"
+echo(x) # "File name is: /etc/hosts"
+```
+
+If you need `$` literals in your command, you
+simply need to escape them with a `\`:
+
+``` bash
+"$non_existing_var" # "" since the ABS variable 'non_existing_var' doesn't exist
+"\$non_existing_var" # "$non_existing_var"
+```
+
 ## Special characters embedded in strings
 
 Double and single quoted strings behave differently if the string contains
diff --git a/evaluator/evaluator.go b/evaluator/evaluator.go
index c6f8bb0d..2eac6cfd 100644
--- a/evaluator/evaluator.go
+++ b/evaluator/evaluator.go
@@ -93,7 +93,7 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 		return NULL
 
 	case *ast.StringLiteral:
-		return &object.String{Token: node.Token, Value: node.Value}
+		return &object.String{Token: node.Token, Value: util.InterpolateStringVars(node.Value, env)}
 
 	case *ast.Boolean:
 		return nativeBoolToBooleanObject(node.Value)
diff --git a/evaluator/evaluator_test.go b/evaluator/evaluator_test.go
index e2adb047..c970b986 100644
--- a/evaluator/evaluator_test.go
+++ b/evaluator/evaluator_test.go
@@ -365,6 +365,22 @@ func TestStringWriters(t *testing.T) {
 	}
 }
 
+func TestStringInterpolation(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{`a = "123"; "abc$a"`, "abc123"},
+		{`a = "123"; "abc\$a"`, "abc$a"},
+		{`a = "123"; "$$a$$a$$a"`, "$123$123$123"},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testStringObject(t, evaluated, tt.expected)
+	}
+}
+
 func TestForInExpressions(t *testing.T) {
 	tests := []struct {
 		input    string
diff --git a/examples/ip-sum.abs b/examples/ip-sum.abs
index 5248021f..2c1d01ea 100644
--- a/examples/ip-sum.abs
+++ b/examples/ip-sum.abs
@@ -8,5 +8,5 @@ if !res.ok {
 ip = res.json().ip
 total = ip.split(".").map(int).sum()
 if total > 100 {
-    echo("The sum of [%s] is a large number, %s.", ip, total)
+    echo("The sum of [$ip] is a large number, $total.")
 }
\ No newline at end of file
diff --git a/scripts/release.abs b/scripts/release.abs
index d115bbda..1c7dd021 100644
--- a/scripts/release.abs
+++ b/scripts/release.abs
@@ -54,7 +54,7 @@ if !rm.ok {
 
 version = `cat ./main.go | grep "var Version"`
 version = version.slice(15, len(version) - 1)
-echo("Running builds for version %s, confirm by typing \"y\"".fmt(version))
+echo("Running builds for version $version, confirm by typing \"y\"")
 selection = stdin()
 
 if selection != "y" {
@@ -63,7 +63,7 @@ if selection != "y" {
 
 for platform in platforms {
     goos, goarch = platform.split("/")
-    output_name = "builds/abs-%s-%s-%s".fmt(version, goos, goarch)
+    output_name = "builds/abs-$version-$goos-$goarch"
     entry_point = "main.go"
 
     if goos == "windows" {