From 74aff5401b003cd530fd64dba4d3eddf1c9e38b1 Mon Sep 17 00:00:00 2001
From: Gaith Hallak <gaithhallak@gmail.com>
Date: Tue, 12 Apr 2022 12:40:32 +0300
Subject: [PATCH] Introduce pipe operator |> (#371)

* Add pipe operator

* Add tests

* Update docs and CHANGELOG
---
 CHANGELOG.md                     |  4 ++++
 docs/sophia_syntax.md            |  3 +++
 src/aeso_ast_infer_types.erl     |  7 ++++++-
 src/aeso_ast_to_fcode.erl        |  7 +++++--
 src/aeso_parser.erl              |  7 ++++---
 test/aeso_compiler_tests.erl     |  1 +
 test/contracts/pipe_operator.aes | 18 ++++++++++++++++++
 7 files changed, 41 insertions(+), 6 deletions(-)
 create mode 100644 test/contracts/pipe_operator.aes

diff --git a/CHANGELOG.md b/CHANGELOG.md
index af0a454..13a2b52 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Added
 - Compiler warnings for the follwing: shadowing, negative spends, division by zero, unused functions, unused includes, unused stateful annotations, unused variables, unused parameters, unused user-defined type, dead return value.
+- The pipe operator |>
+  ```
+  [1, 2, 3] |> List.first |> Option.is_some  // Option.is_some(List.first([1, 2, 3]))
+  ```
 ### Changed
 - Error messages have been restructured (less newlines) to provide more unified errors. Also `pp_oneline/1` has been added.
 ### Removed
diff --git a/docs/sophia_syntax.md b/docs/sophia_syntax.md
index db438b5..b9c6aa0 100644
--- a/docs/sophia_syntax.md
+++ b/docs/sophia_syntax.md
@@ -234,6 +234,7 @@ Path ::= Id                 // Record field
 
 BinOp ::= '||' | '&&' | '<' | '>' | '=<' | '>=' | '==' | '!='
         | '::' | '++' | '+' | '-' | '*' | '/' | 'mod' | '^'
+        | '|>'
 UnOp  ::= '-' | '!'
 ```
 
@@ -245,6 +246,7 @@ UnOp  ::= '-' | '!'
 | `!` `&&` `\|\|` | logical operators
 | `==` `!=` `<` `>` `=<` `>=` | comparison operators
 | `::` `++` | list operators
+| `\|>` | functional operators
 
 ## Operator precendences
 
@@ -261,3 +263,4 @@ In order of highest to lowest precedence.
 | `<` `>` `=<` `>=` `==` `!=` | none
 | `&&` | right
 | `\|\|` | right
+| `\|>` | left
diff --git a/src/aeso_ast_infer_types.erl b/src/aeso_ast_infer_types.erl
index 0e87869..4ef4403 100644
--- a/src/aeso_ast_infer_types.erl
+++ b/src/aeso_ast_infer_types.erl
@@ -1941,7 +1941,12 @@ infer_infix({'::', As}) ->
 infer_infix({'++', As}) ->
     ElemType = fresh_uvar(As),
     ListType = {app_t, As, {id, As, "list"}, [ElemType]},
-    {fun_t, As, [], [ListType, ListType], ListType}.
+    {fun_t, As, [], [ListType, ListType], ListType};
+infer_infix({'|>', As}) ->
+    ArgType = fresh_uvar(As),
+    ResType = fresh_uvar(As),
+    FunType = {fun_t, As, [], [ArgType], ResType},
+    {fun_t, As, [], [ArgType, FunType], ResType}.
 
 infer_prefix({'!',As}) ->
     Bool = {id, As, "bool"},
diff --git a/src/aeso_ast_to_fcode.erl b/src/aeso_ast_to_fcode.erl
index f0ca66a..5194340 100644
--- a/src/aeso_ast_to_fcode.erl
+++ b/src/aeso_ast_to_fcode.erl
@@ -703,8 +703,11 @@ expr_to_fcode(Env, _Type, {block, _, Stmts}) ->
 expr_to_fcode(Env, _Type, Expr = {app, _, {Op, _}, [_, _]}) when Op == '&&'; Op == '||' ->
     Tree = expr_to_decision_tree(Env, Expr),
     decision_tree_to_fcode(Tree);
-expr_to_fcode(Env, _Type, {app, _Ann, {Op, _}, [A, B]}) when is_atom(Op) ->
-    {op, Op, [expr_to_fcode(Env, A), expr_to_fcode(Env, B)]};
+expr_to_fcode(Env, Type, {app, Ann, {Op, _}, [A, B]}) when is_atom(Op) ->
+    case Op of
+        '|>' -> expr_to_fcode(Env, Type, {app, Ann, B, [A]});
+        _    -> {op, Op, [expr_to_fcode(Env, A), expr_to_fcode(Env, B)]}
+    end;
 expr_to_fcode(Env, _Type, {app, _Ann, {Op, _}, [A]}) when is_atom(Op) ->
     case Op of
         '-' -> {op, '-', [{lit, {int, 0}}, expr_to_fcode(Env, A)]};
diff --git a/src/aeso_parser.erl b/src/aeso_parser.erl
index 79d7a8b..7e5fa62 100644
--- a/src/aeso_parser.erl
+++ b/src/aeso_parser.erl
@@ -308,17 +308,18 @@ expr() -> expr100().
 
 expr100() ->
     Expr100 = ?LAZY_P(expr100()),
-    Expr200 = ?LAZY_P(expr200()),
+    Expr150 = ?LAZY_P(expr150()),
     choice(
     [ ?RULE(lam_args(), keyword('=>'), body(), {lam, _2, _1, _3})   %% TODO: better location
-    , {'if', keyword('if'), parens(Expr100), Expr200, right(tok(else), Expr100)}
-    , ?RULE(Expr200, optional(right(tok(':'), type())),
+    , {'if', keyword('if'), parens(Expr100), Expr150, right(tok(else), Expr100)}
+    , ?RULE(Expr150, optional(right(tok(':'), type())),
             case _2 of
                 none       -> _1;
                 {ok, Type} -> {typed, get_ann(_1), _1, Type}
             end)
     ]).
 
+expr150() -> infixl(expr200(), binop('|>')).
 expr200() -> infixr(expr300(), binop('||')).
 expr300() -> infixr(expr400(), binop('&&')).
 expr400() -> infix(expr500(),  binop(['<', '>', '=<', '>=', '==', '!='])).
diff --git a/test/aeso_compiler_tests.erl b/test/aeso_compiler_tests.erl
index fe3a130..fa3cb6a 100644
--- a/test/aeso_compiler_tests.erl
+++ b/test/aeso_compiler_tests.erl
@@ -218,6 +218,7 @@ compilable_contracts() ->
      "using_namespace",
      "assign_patterns",
      "patterns_guards",
+     "pipe_operator",
      "test" % Custom general-purpose test file. Keep it last on the list.
     ].
 
diff --git a/test/contracts/pipe_operator.aes b/test/contracts/pipe_operator.aes
new file mode 100644
index 0000000..fc7248f
--- /dev/null
+++ b/test/contracts/pipe_operator.aes
@@ -0,0 +1,18 @@
+contract Main =
+    function is_negative(x : int) =
+        if (x < 0)
+            true
+        else
+            false
+
+    function inc_by_one(x : int) = x + 1
+    function inc_by_two(x : int) = x + 2
+
+    type state = bool
+
+    entrypoint init(x : int) = x
+        |> inc_by_one
+        |> inc_by_one
+        |> inc_by_two
+        |> ((x) => x * 5)
+        |> is_negative